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Ngo, Kim Phuong Yen. "Valeur pronostique des biomarqueurs non-invasifs chez les sujets infectés par le virus de l'hépatite C ou B." Paris 6, 2008. http://www.theses.fr/2008PA066202.
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Les infections chroniques par le virus de l’hépatite B (VHB) et le virus de l’hépatite C (VHC) sont des problèmes majeurs de santé publique à l'échelle mondiale. Il est primordial d’améliorer l’évaluation de la gravité de ces hépatites chroniques pour mieux rationaliser la prise en charge des patients. La ponction biopsie hépatique (PBH) était jusqu’à présent le « gold standard » pour le diagnostic et le pronostic de la fibrose hépatique. Cependant ses nombreuses limitations, effets secondaires sévères, et une fréquence élevée de faux négatifs et de faux positifs, on conduit ces dernières années à l’élaboration de biomarqueurs, utilisés seuls ou en combinaison. Aucune estimation des valeurs pronostiques de ces marqueurs non-invasifs n’a été réalisée. Le but de notre thèse a été de démontrer la valeur pronostique du FibroTest-ActiTest (FT-AT) chez les patients infectés par le VHC et le VHB. Nous avons pu participer à deux travaux sur 2 populations distinctes: Une cohorte prospective de 537 patients ayant une infection chronique par le VHC, chez qui le stade de fibrose et le grade d’activité ont été évalués le même jour par une ponction biopsie hépatique et par FT-AT. Une cohorte prospective de 1300 patients ayant une infection chronique par le VHB, chez qui le stade de fibrose, le grade d’activité par FT-AT et la charge virale VHB ont été évalués le même jour. Le but de ces deux travaux principaux de ces quatre années de Thèse était d’estimer et de comparer les valeurs pronostiques des nouveaux biomarqueurs (FT-AT, Score APRI, Score de Forns) et du score pronostique « standard » classique (Score de Child-Pugh) pour prédire la survenue des complications et la survie chez les patients ayant une infection chronique par le VHB ou le VHC. Les analyses de survie, méthodes univariée et multivariée, ont estimé la valeur pronostique des stades de fibrose (estimés par biopsie hépatique et par biomarqueurs) et des autres facteurs potentiellement prédictifs de la survenue des complications de la cirrhose et de la survie. La durée de survie a été calculée à partir de la date du FT-AT à la date de la survenue du premier évènement (complications de la maladie, décès toutes causes et décès lié au foie); puis comparée à la survie attendue dans la population française (avec appariement sur l’âge, le sexe, l’année d’inclusion et la durée de suivi). Les valeurs pronostiques de la biopsie hépatique et des biomarqueurs ont été estimées et comparées par les aires sous les courbes pronostiques ROC (AUROC). RESULTATS Travail sur la cohorte de 537 patients atteints de l’hépatite chronique CRésultats à 5 ans de suivi (publication en 2005). Les patients avec fibrose sévère avaient une survie sans complications ou décès liés au VHC à 78. 5% (IC 95% = [71. 2%-85. 9%]; 28 complications ou décès liés au VHC) et une survie sans décès lié au VHC de 92. 7% (88. 0%-97. 3%; 9 décès liés au VHC). Les patients avec fibrose modérée avaient une survie sans complications ou décès liés au VHC à 98. 8% (96. 6%-100%; 1 complication, P<0. 001) et une survie sans décès lié au VHC à 100% (aucun décès lié au VHC; P<0. 001). Les patients avec fibrose minime avaient une survie sans complications ou décès liés au VHC à 100% (aucune complication liée au VHC; P<0. 001) et une survie sans décès lié au VHC à 100% (aucun décès lié au VHC; P<0. 001). Le FT avait une meilleure valeur pronostique par rapport à la biopsie, pour la survenue des complications avec une AUROC [IC 95%] =0. 96 [0. 93-0. 97] vs 0. 91 [0. 85-0. 94; P=0. 01] et pour la survenue de décès lié au VHC: AUROC = 0. 96 [0. 93-0. 98] vs 0. 87 [0. 70-0. 94; P=0. 046]. La valeur pronostique du FT était significativement plus élevée par rapport à celle des autres scores (APRI, Forns, Pugh) en analyse univariée (P<0. 001) et en régression logistique (P<0. 01) prenant en compte la réponse au traitement et les autres facteurs pronostiques connus (co-infection VIH, consommation d’alcool). Résultats à 8 ans de suivi (rédaction d’article en cours en 2008). Les patients avec fibrose sévère avaient une survie sans complications ou décès liés au VHC à 71. 0% (IC 95% = [63. 0%-79. 1%]; 39 complications ou décès liés au VHC) et une survie sans décès lié au VHC de 76. 5% (66. 8%-86. 2%; 24 décès liés au VHC). Les patients avec fibrose modérée avaient une survie sans complications ou décès liés au VHC à 97. 0% (93. 5%-100%; 3 complications ou décès liés au VHC, P<0. 0001) et une survie sans décès lié au VHC à 89. 3% (73. 6%-100%; 3 décès liés au VHC; P<0. 0001). Les patients avec fibrose minime avaient une survie sans complications ou décès liés au VHC à 99. 5% (98. 6%-100%; 1 complication; P<0. 0001) et une survie sans décès lié au VHC à 99. 5% (98. 6%-100%; 1 décès lié au VHC; P<0. 0001). FT avait une meilleure valeur pronostique par rapport à la biopsie, pour la survenue des complications ou décès liés au VHC avec une AUROC [IC 95%] = 0. 91 [0. 86-0. 94] vs 0. 77 [0. 66-0. 85; P=0. 0006] et pour la survenue de décès lié au VHC: AUROC = 0. 88 [0. 79-0. 92] vs 0. 66 [0. 49-0. 78; P=0. 0002]; et pour la survie globale: AUROC = 0. 75 [0. 64-0. 82] vs 0. 56 [0. 44-0. 66; P=0. 0002]. La valeur pronostique du FT restait significative en régression logistique (P<0. 001) prenant en compte la réponse au traitement et les autres facteurs pronostiques connus. Travail sur la cohorte de 1300 patients atteints de l’hépatite chronique B (Article en cours de soumission, version révisée en cours). Parmi les 1074 patients inclus, il a été observé 50 complications avec ou sans décès liés au foie [survie sans complications ou décès liés au foie = 93. 4% (IC 95% = 91. 4%-95. 4%)], 36 décès [survie sans décès= 95. 0% (93. 2%-96. 8%)] avec 27 décès liés au foie [survie sans décès liés au foie = 96. 1% (94. 4%-97. 8%)]. FT avait une meilleure valeur pronostique par rapport à la charge virale ou aux ALT pour la survenue des complications ou décès liés au foie [AUROC=0. 89 (IC 95% 0. 84-0. 93) vs 0. 64 (0. 55-0. 71) vs 0. 53 (0. 46-0. 60); (P<0. 0001)], et une meilleure valeur pronostique dans l’analyse multivariée [coefficient de régression 5. 2 (3. 5-6. 9; P<0. 0001) vs 0. 53 (0. 2-0. 9; P=0. 007) vs -0. 001 (-0. 003-0. 000; P=0. 052)]. Une nouvelle définition du statut de porteur inactif du VHB est proposée avec un algorithme associant la charge virale et le score de FibroTest-ActiTest. Ce nouvel algorithme présente une valeur prédictive négative à 100% pour les décès liés au foie et/ ou complications. Parmi les 275 patients classés porteurs inactifs d’après la définition classique, 62 patients (22. 5%) avaient une fibrose présumée par FT, et 3 sont décédés ou ont eu des complications dans les 4 ans du suivi. Chez les patients ayant une infection chronique par le VHC, le FibroTest est un marqueur biochimique de la sévérité de la maladie avec une valeur pronostique à cinq ans et à huit ans meilleure que celle de l’histologie pour la prédiction des complications et des décès liés au VHC. Chez les patients ayant une infection chronique par le VHB, le FibroTest a une valeur pronostique à quatre ans similaire à celle de la biopsie hépatique. La combinaison de FibroTest-ActiTest et la charge virale permet de définir avec plus de précision le pronostic et le statut de « porteur inactif » que la définition classique.
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Allsop, Thomas David Paul. "A fibre optical strain sensor." Thesis, University of Plymouth, 1999. http://hdl.handle.net/10026.1/2779.
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Strain-sensing elements, fabricated in standard communications-grade single mode optical fibre, are increasingly being considered for application in structural health monitoring. The reason for this is the numerous advantages demonstrated by these devices compared with traditional indicators. This thesis describes work carried out on optical sensors at the University of Plymouth. The aim of this work was to achieve an optical fibre strain sensing system capable of measuring absolute strain with good resolution and having wide dynamic range, without bulky optical equipment and not susceptible to misalignment due to handling. Earlier work was devoted to study on an intrinsic Fabry-Perot interferometric sensor and an optical phase-shift detection technique. The sensing element investigated relied on the end face of an optical fibre as one mirror and the second mirror being a layer of Titanium Dioxide (TO2). Although some results are included, it was soon realised that this sensor had a number of problems, particularly with fabrication. As no simple solution presented itself, consideration was given to a sensor that made use of the change in reflectance of an intra-core fibre Bragg grating when the grating was subjected to strain. The bulk of work described in this thesis is concerned with this type of sensing element. The grating structure is inherently flexible and a number of structural formats were studied and investigated. The first and simplest grating considered was two linearly chirped Bragg gratings used in a Fabry-Perot configuration (a grating resonator). The sensor was tested using the sensing detection system and although the fabrication problems were overcome absolute strain measurement was unattainable. To achieve this end, a theoretical study of a number of grating structures was carried out using the T-matrix Formalism. Confidence in using this approach was gained by comparing the spectral behaviour of a proposed grating with results, which were given by another theoretical model for the same proposed grating. The outcome of this study was that two structures in particular showed promise with regard to absolutism (the measure of true strain) and linearity. Discussions held with the department of Applied Physics at Aston University about fabrication resulted in one of the proposed designs being abandoned due to difficulties of fabrication. The second structure showed more promise and fabrication attempts were put in hand. This grating is linearly-chirped with a Top-hat function and a sinusoidal perturbation as a taper function of the refractive index modulation. Experiments were performed, data were acquired and system performance for this sensor is presented. The thesis concludes that using such a fibre Bragg grating as the sensing element of a strain sensing system enables it to measure absolute strain without using bulky optical equipment. At present, the resolution of strain is limited by the quality of the grating being fabricated (anomalies on profile), this should improve once the fabrication technique is refined.
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Saleh, Najia M. "Bond of glass fibre reinforced polymer bars in high strength concrete." Thesis, University of Bradford, 2018. http://hdl.handle.net/10454/17361.
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Very limited research studies have been conducted to examine bond of glass fibre reinforced polymer (GFRP) bars with high concrete strength. The current research project aims to compare between bond measured from a pull-out test and a hinged beam test for GFRP bars embedded in high strength concrete. Different parameters influencing bond such as GFRP bar diameter, embedment length and surface configuration were investigated in both test methods, while the bar position, i.e. top or bottom, was only studied in hinged beams.
Seventy-two pull-out cubes, eight pull-out prisms and twenty-four hinged beams reinforced with GFRP bars were constructed and tested to failure. Twelve pull-out cubes and four hinged beams reinforced with steel bars were also tested for comparison purposes. The results showed that bond stress – slip curves obtained from various testing methods were similar, consisting of high initial stiffness, followed by nonlinear ascending and softening branches. In addition, it was found that the experimental bond strength obtained from hinged beams was higher than both bond strengths measured by the pull-out cube and pull-out prism. However, when a finite element analysis was conducted for hinged beams, it was shown that the tensile force in the reinforcing bar estimated by equilibrium conditions is overestimated as the large deformation of hinged beams at failure was not considered. Therefore, if the tensile force obtained from the finite element analysis is used to calculate the bond strength, it would be similar to that obtained from pull-out cube and prism. Moreover, it was found that the distribution of tensile and bond stresses was nonlinear along the GFRP embedment length and bond stress at the vicinity of the free end increased with increasing the load due to redistribution of bond stresses along the embedment length.
Bond strengths were compared against the prediction methods provided in ACI-440.1R, CSA-S806, CSA-S6 and JSCE 1997. In general, all design codes showed conservative results for all specimens tested and ACI predictions gave a good agreement with experimental data compared to other codes.
Artificial neural network models were developed to predict bond strength of GFRP bars in concrete. These models used bar diameter, embedment length, concrete compressive strength and concrete cover as input variables. The developed ANN models showed to be able to predict bond strength of GFRP bars in concrete and, therefore, were used to conduct a parametric study.Higher Education Institute, Government of Libya
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Sandbakk, Sindre. "Fibre Reinforced Concrete : Evaluation of test methods and material development." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15156.
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Concrete is a structural material with excellent properties when subjected to compression, butthe abilities to resist tensile stresses are rather poor. The concrete’s tensile zone is normallyreinforced with large continuous steel bars, a combination which ensures an excellentconstruction material. Placing the re-bars generates many man-hours, which means that the reinforcement work accounts for a considerable part of the total concrete cost. An alternative to the conventional re-bars is fibre reinforced concrete. Fibre reinforced concrete is concrete reinforced with small randomly distributed discontinuous fibres instead of large unidirectional continuous steel bars. In cases where thestrength and ductility of fibre reinforced concrete is sufficient with regard to the actions, fibrereinforced concrete can be an adequate and cheaper alternative to conventionally reinforced concrete. If fibres are used together with conventional re-bars, both the total load carryingcapacity and the stiffness of the structure will increase, and the crack widths will decrease. One working hypothesis in the present thesis has been that the behaviour of fibre reinforced concrete can be uniquely described by the fibre slip, and an objective has been to investigate whether this hypothesis is correct or not. Due to the fact that the maximum fibre stress achieved during pull-out test is considerably less than the fracture stress for most fibre types,it is reasonable to assume that the fibres’ pull-out length in a real structure is identical with the crack width, because the fibres will simply loosen at the weakest side of a crack. Based on alarge number of experiments, and some simplified models which relate the experimental results to crack openings, it seems like the working hypothesis is correct. A theoretical relation between the results from energy absorption test found by two differenttest codes is established. This relation is based on the above mentioned working hypothesis,and it is shown that the theoretical relation corresponds well to an empirical relation found in the literature. A second objective has been to show that fibre reinforcement actually has sufficient strength and ductility to be used as a replacement to conventional re-bars in some types of concretestructures. A concrete called ductile high tensile strength all round concrete is developed, and this concrete shows promising properties with regard to both shear strength, bending strength and ductility. The last few pages of the present thesis deals with some paradoxes from some of the material models used to describe fibre reinforced concrete from the literature. The experiences from the experimental work, and the analyses of the results, indicate that the fibre efficiency is increased by increasing crack widths until the crack widths reaches a certain level, while most of the models suggest that fibres are most effective at smaller crack widths.
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Sun, Jianan. "Peel test for the study of the fibre polymer interface." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ58749.pdf.
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Algassem, Omar. "Parameters Affecting the Blast Performance of High Strength Fibre Reinforced Concrete Beams." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35022.
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A limited number of studies have been conducted in the literature in order to investigate the behaviour of high-strength fibre-reinforced concrete (HSFRC) structural components subjected to blast loads. This study summarizes the results of a research program investigating the potential of using steel fibres to improve the blast performance of high-strength reinforced concrete beams. As part of the experimental investigation twenty beams were tested, including nine beams tested under static four-point bending, and eleven beams tested under dynamic blast loads using a shock-tube. Parameters considered in the study include the effect of concrete strength, steel fibres, fibre content, fibre type, longitudinal reinforcement ratio, and presence of shear reinforcement. All beams in the study have identical dimensions, with a cross-section of 125 x 250 mm and length of 2440 mm. To manufacture the specimens, two beams were cast with normal-strength self-consolidate concrete (SCC), with a specified strength of 50 MPa, while the remaining beams were cast with either plain or fibre-reinforced high-strength concrete having a compressive strength which varied between 95-110 MPa. The steel fibre content in the HSFRC beams varied between 0.5 and 1.0%, by volume of concrete. To investigate the effect of reinforcement ratio (ρ), the beams were reinforced with 2-#4 (American size) bars, 2-15M bars or 2-20M bars (ρ = 1.02%, 1.59%, and 2.41%, respectively). The majority of the plain concrete beams had transverse reinforcement which consisted of 6 mm stirrups arranged at a spacing of 100 mm in the shear spans, while most of the HSFRC beams were built without stirrups. The results indicate that all the parameters in this study (reinforcement ratio, presence of stirrups, concrete strength, steel fibres, fibre content and fibre type) affected the static and blast response of the beams, however, the results demonstrate that steel fibres have a more remarkable effect when compared to the other parameters. The provision of fibres is found to improve the blast performance of the HSC beams by increasing shear capacity, reducing maximum and residual mid-span displacements, reducing blast fragments and increasing damage tolerance.
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Chan, Mimi Mingsze. "Transverse tests for fibre-polymer adhesion evaluation." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0007/MQ45578.pdf.
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Zettwoch, Robert N. "FLIGHT TEST MONITORING OF AVIONIC FIBRE CHANNEL NETWORKS FOR RECORDING AND TELEMETRY." International Foundation for Telemetering, 2003. http://hdl.handle.net/10150/606696.
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International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, NevadaThe F/A-18E/F Super Hornet fighter aircraft program is currently flight testing a Fibre Channel Network (FCN), which will initially replace certain Avionics Systems’ MIL-STD-1553 communications. The Advanced Mission Computers and Displays (AMC&D) and the Active Electronically Scanned Array (AESA) RADAR are replacing their MIL-STD-1553 counterparts to fulfill performance enhancements and growing data requirements. The maximum amount of data that can be transferred between these systems is significantly increasing. Each remote terminal on a MIL-STD-1553 bus can transmit or receive approximately 1Mbps. Each node on a FCN can simultaneously transmit and receive 1Gbps. With a Fibre Channel Network Switch (FCNS), multiple systems can communicate concurrently, thus increasing overall system throughput even further. Several other systems will be replaced in the near future utilizing the FCNS. The Fibre Channel Interface Unit (FCIU) was designed for the F/A-18E/F AESA program as a nonintrusive way to monitor multiple nodes, extract node specific information, and record this information using conventional on-board recorders. In order to reduce the risks associated with developing hardware and software concurrently with the Avionic System’s protocol, the FCIU was developed as an upper-level-protocol (ULP) (layer FC-4) independent device. Two big advantages of ULP independence are the avoidance of complex protocol programming for each different type of monitored network system and the non-intrusive nature of the FCIU connection to the FCN. This facilitates the quick installation of the FCIU to monitor any FC network and the FCIU IRIG-106 PCM type output lends itself to be integrated quickly into a typical Flight Test data recording or telemetry system.
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Tao, Yi. "Fibre reinforced polymer (FRP) strengthened masonry arch structures." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7743.
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Masonry arch bridges have played a significant role in the road and rail transportation network in the world for centuries. They are exposed to damage due to overloading and deterioration caused by environmental actions. In order to reestablish their performance and to prevent their collapse in various hazardous conditions, many of them require strengthening. Fibre reinforced polymer (FRP) systems are increasingly used for repair and strengthening of structures, with particularly widespread application to concrete structures. However, the application of FRP composites to masonry structures is less well established due to the complexity of masonry caused by the material discontinuity. FRP strengthening masonry arch bridges has been even less studied due to the additional complexity arising from the co-existence of the normal interfacial stress and the shear interfacial stress at the curved FRP-to-masonry bondline. This thesis presents an extensive study investigating the behaviour of FRP strengthened masonry bridges. The study started with a laboratory test of a two span masonry arch bridge with sand backfill. A single ring arch bridge was first tested to near failure, and then repaired by bonding FRP into their intrados and tested to failure. It was found that the FRP strengthening not only improved the loading capacity and stiffness of bridge, but also significantly restrained the opening of cracks in the masonry. Shear and peeling debonding of FRP was observed. There have been two common strategies in finite element (FE) modelling of FRP strengthened structures in meso-scale: direct model and interface model. The former is necessary when investigating the detailed bond behaviour but challenges remain due to the difficulties in concrete modelling. A new concrete damage model based on the plastic degradation theory has been developed in this study to study the bond behaviour of FRP strengthened concrete structure. This robust model can successfully capture this bond behaviour and simulate the entire debonding process. A numerical study of masonry arch bridges including the backfill was conducted to study the behaviour of masonry arch bridge. A total of four modelling strategies were examined and compared. Although they all can successfully predict the behaviour of arch, a detailed solid model newly developed in this study is more suitable for modelling both plain masonry and FRP strengthened structures. Finally, a numerical study of bond behaviour and structural response of FRP strengthened masonry arch structures with sand backfill was conducted. In addition to the masonry and backfill, the mixed mode interfacial behaviour was modelled by the aforementioned interface model strategy and investigated in detail to achieve a deeper understanding of the behaviour of FRP strengthened masonry arch structures. The results are in close agreement with test results, and highlight the influence of the key parameters in the structural response to failure and revealed the mechanisms on how the load is transmitted through this complex multi-component structural system.
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Cámara, Vela Juan Antonio, and Molina Juan Manuel Sánchez. "Design of a Double Cantilever Beam Test Specimen and Fixture for Kink Band Formation in Unidirectional Fibre Reinforced Composites." Thesis, Högskolan i Skövde, Institutionen för ingenjörsvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-11218.
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Composite materials are widely used in demanding applications in aerospace and other industries. In order to understand the complex behaviour of the composite materials and their components, standardised test methods are used. One example is the double cantilever beam (DCB) test in which the test specimen is loaded in an opening, i.e., tensile mode. Failures in composite materials loaded compression are different from those in tension, for example, kink band or buckling-like failures can occur. In this project, several DCBs are designed and a new fixture which allows for compression testing of a DCB is developed for an existing Instron testing machine. The fixture overcomes a known problem of tensile peak causing the failure of the adhesive at the inner surfaces of the DBC by applying additional compressive loads along the outer surfaces of the DBC. The compressive forces can induce the desired kink band formation so that researchers can better study the failure mode. The conceptual development of the new DCBs and the new fixture are presented. Several prototypes of the specimens and the fixture are modelled using the three-dimensional (3D) computer-aided design software Creo Parametric 2.0. One of the fixtures is selected to further study. The different DCB specimens are studied in order to obtain information about the kink band using 3D finite element analysis with the software programme Abaqus CAE. The selected fixture is analysed to determine if there are any areas of concern. Finally, the behaviour of the compression stress along the DCB using two pairs of forces is studied. Unfortunately, it is determined that the tensile peak experienced by the adhesive cannot be eliminated by the application of two pairs of compressive loads, one at the free end and the other in the vicinity of the tensile peak. Several suggestions are made for future work which might serve to reduce the tensile peak; e.g., the movable force couple is applied as a surface load instead of a point load. For this, the fixture will have to be modified with a new geometry, although the DCB could be the same. This will allow further work to focus on the combined behaviour of the tensile peak and the fixture.
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Davenport, Rebecca A. "An investigation into the manufacture and mechanical properties of an Al-steel hybrid MMC." Thesis, Brunel University, 2018. http://bura.brunel.ac.uk/handle/2438/17033.
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One of the most significant challenges in the composite development field is to find a low-cost manufacturing route capable of producing large volumes of material. This thesis develops and characterises a potential avenue for addressing this, an induction furnace-based process. This process produced a composite of A357 matrix and 10% wt Dramix 3D 80/30 SL steel fibres. The method was evaluated by microstructural analysis and optimum casting parameters were approximated. The fibres were introduced to liquid A357 at 700°C and the composite was brought to a measured temperature of 650°C over not more than 120 seconds before being removed from the furnace and cooled. 10% wt was the ideal reinforcement ratio for this process. Characterising the tensile and compressive strength of the composite material, it reached a peak stress 130% higher than A357 produced under the same conditions, though the peak stresses were still 20% of the literature values for T6 tempered A357. This suggests the need for development of a temper which does not degrade the properties of the composite. 3-point bending tests and some tensile specimens also showed post-failure strength. Under dynamic loading, the composite showed a peak stress in excess of 100 MPa without reaching maximum compression under SHPB loading, and comparable performance to SiC-reinforced MMCs under ballistic testing. The linear decrease in work-hardening with increasing distance from the impact site shows shock and pressure-pulse dissipation properties, attributed to the difference in acoustic impedance between the matrix and the reinforcement.
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Carvalho, Carlos Augusto Ramos de. "Efeito da técnica úmida simplificada de adesão com etanol na cimentação intraradicular de pinos de fibra." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/25/25131/tde-05122011-092428/.
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Este estudo avaliou a resistência ao deslocamento vertical push-out de pinos de fibra de vidro cimentados à dentina intra-radicular utilizando uma resina fluida padrão como agente cimentante em combinação com um adesivo dentinário experimental e um adesivo disponível comercialmente. 20 pré-molares unirradiculares humanos foram previamente extraídos e tratados endodonticamente. Os espécimes foram divididos em quatro estratégias de união a dentina: Grupo 1 com adesivo experimental com etanol na proporção em volume 1:1 (resina/etanol) e Grupo 2 com adesivo experimental com etanol na proporção em volume 1:2(resina/etanol); adesivos experimentais aplicados de acordo com a técnica úmida de adesão simplificada com etanol, Grupo 3: One-Step Plus aplicado de acordo com a técnica úmida de adesão simplificada com etanol; Grupo 4: One-Step Plus aplicado seguindo as instruções do fabricante. Os espécimes foram seccionados em fatias de 1 mm de espessura e apos o teste push-out foi realizado. Espécimes representativos foram selecionados para exame ultra-estrutural. Não houve diferença estatística na resistência ao deslocamento push-out entre as estratégias testadas de adesão (p> 0,05). O padrão predominante de fratura foi entre os pinos de fibra e o agente cimentante. A partir deste estudo devemos considerar como promissora a técnica com etanol utilizada na cimentação de pinos no canal radicular devido aos possíveis benefícios das resinas altamente hidrófobas. Mais estudos são necessários para validar o uso da técnica úmida de adesão simplificada com etanol quando cimentados pinos de fibra.This study evaluated the push-out bond strength of glass fiber posts adhesively bonded to intraradicular dentin using a standard unfilled resin as luting agent in combination with an experimental and a commercially available adhesive. Twenty extracted single-rooted human teeth were endodontically treated. Specimens were assigned to 4 dentin bonding strategies: Group 1 (co-monomers to ethanol on ratio 1:1) and Group 2 (co-monomers to ethanol on ratio 1:2): Experimental adhesives applied in accordance with the simplified ethanol-wet bonding technique; Group 3: One-Step Plus (OSP) applied in accordance with the simplified ethanol-wet bonding technique; Group 4: OSP applied following manufacturers instructions. Bonded specimens were sectioned in 1-mm-thick slices and the push-out test was performed. Representative specimens were selected for ultrastructural examination. No statistical differences in push-out bond strength were found among the tested bonding strategies (p>0.05). The major failure pattern was between the post and the luting cement. From this study the ethanol technique should be considered as a promising approach in the luting of fiber posts into the root canal due to the possible benefits of highly hydrophobic resins. Further studies are needed to validate the use of the ethanol-wet bonding technique when luting a fiber post.
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Brooks, W. G. "The design, construction and test of a postbuckled, carbon fibre reinforced plastic wing box." Thesis, Cranfield University, 1987. http://hdl.handle.net/1826/3292.
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A postbuckled, carbon fibre reinforced plastic (CFRP)
wing box has been designed, manufactured and tested
for an aerobatic light aircraft, the Cranfield Al.
Methods of analysis have been evaluated including:
i) Non-linear finite element analysis for the
prediction o-f panel postbuckling.
ii) A simpler technique based on an effective
width method. This forms the core of a design program,
'oPTIMIST'. It predicts buckling loads, postbuckled
reduced stiffness and overall column failure of
co-cured hat stiffened panels. It then optimises the
con-Figuration of a box beam for minimum weight.
iii) The use of the effective width method allied
to a large scale, linear finite element analysis.
The work includes the development of a new method
o-F construction for composite box structures. The wing
skin sti-Ffeners and rib flanges are co-cured
together. Integral slotted Joint features are formed
in each part. The structure is then adhesively bonded
together. A full description of the manufacture o-F the
wing box is included.
The structure was also tested in a specially
designed rig. It was tested to ultimate design loads
in:
i) Positive bending to 13.33.
ii) Negative bending to -96.
iii) Pure torsion resulting from full aileron
load.
iv) Torsion with 96 bending.
The compression panels were seen to postbuckle and
recover in each load case. Results are compared with
theory, and with the original aluminium Al wing. The
structure is 257. lighter than its aluminium
counterpart.
Finally, suggestions are made for possible areas
of further research.
14
Vasconcelos, Rafaela Andrade de [UNESP]. "Avaliação da influência de materiais obturadores endodônticos sobre a resistência de união adesiva de pinos de fibra de vidro cimentados." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/138113.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O propósito deste estudo foi avaliar, in vitro, a influência de remanescente de materiais obturadores endodônticos, após desobturação e preparo para pino, sobre a resistência de união adesiva de pinos de fibra de vidro cimentados. Foram utilizados 60 dentes humanos unirradiculados sem coroa. As raízes foram preparadas pela técnica coroa-ápice com sistema Reciproc. Para obturação, as raízes foram divididas em grupos (n = 10) de acordo com o cimento endodôntico utilizado: SO= sem obturação; GP=guta percha sem cimento; AHP= guta-percha + AHPlus; SLP= guta-percha + Sealapex; IRT= guta-percha + iRoot SP; e ERZ= guta-percha + EndoRez. As raízes foram obturadas pela técnica do cone único. A cimentação dos pinos de fibra de vidro Rebilda n.12 foi realizada com sistema adesivo futurabond DC e cimento Rebilda DC em 10 mm do comprimento da raiz. Após esse período, as raízes foram seccionadas obtendo-se discos de 2 mm de espessura em cada terço da raiz (3 discos por raiz) que foram submetidos ao teste de push out, análise por meio de uma lupa estereoscópica (40x) para identificação através de scores da presença de remanescente de material obturador na luz do canal e avaliação por espectroscopia de energia dispersiva (EDS) para identificação de remanescente de componentes químicos do cimento endodôntico presentes nos túbulos dentinários. Os dados obtidos foram analisados estatisticamente pelos testes de Kruskal Wallis, Qui Quadrado e teste de Anova e Tukey, todos com nível de significância de 5%. Não houve diferença estatística para a resistência adesiva entre os cimentos na região cervical (p = 0,49), media (p = 0,28) e apical (p = 0,09). Os grupos SLP e ERZ apresentaram menos remanescente de material obturador nas regiões cervical (p = 0,045) e apical (p = 0,006). Significantes diferenças de remanescentes de componentes químicos foram observadas na região apical dos grupos AHP, IRT e SLP. Conclui-se que os materiais endodônticos não influenciaram na resistência de união adesiva de pinos de fibra de vidro.
The purpose of this study was to evaluate the influence of remnants endodontic filling material in root canal on the bond strength of fiberglass posts cemented. Sixty single-rooted human teeth were used.Crowns were removed. The roots were prepared by crown-down technique with Reciproc system. For fillings, the roots were divided (n = 10) according to the sealer used: SO- without fillings; GP-gutta-percha without sealer; AHP- gutta-percha + AHPlus; SLP- gutta-percha + Sealapex; IRT-gutta-percha + iRoot SP; ERZ-and gutta-percha + EndoRez. Single cone obturation technique was used. After root canal fillings, the teeth were kept in an oven 37 0C for 7 days. Cementing fiberglass posts Rebilda n.12 was performed with fiber adhesive system Futurabond DC and cement Rebilda DC in 10 mm of root length, getting stored in an oven at 37 0C for 48 h. After this period, roots were sectioned obtaining 1 disc of 2 mm thickness in each third of the root (3 discs per root), this discs were underwent to push out test, analyzed by means of a stereomicroscope (40x) to identify the presence of remnants of filling material in the lumen of the canal, and then evaluated by energy dispersive spectroscopy (EDS) for identification of chemical components remnants sealer present in the dentinal tubules. Datas were analyzed with Kruskal-Wallis test, Chi square test, and also Anova and Tukey test, 5% of significance. There were no significant differences in push-out bond strengths among the different groups in the coronal (p = 0.49), middle (p = 0.28) or apical third (p = 0.09). Sealeapex and EndoRez groups showed significantly less remnants of filling material at coronal (p = 0.045) and apical levels (p = 0.006).Significant differences of chemical components remnants were found in AHP, IRT and SLP groups on apical third. It is concluded that residual endodontic filling material does not influence on the bond strength of fiberglass.
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Catalogna, Giammarco. "Fibre di bambù per il rinforzo di malta e intonaco: caratterizzazione meccanica." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
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Nell’ottica della ricerca di un materiale più sostenibile la tesi pone l’attenzione sul rinforzo di malte e intonaci con fibre naturali che sostituiscano quelle artificiali. In particolare, è stata effettuata una caratterizzazione meccanica valutando la resistenza a flessione, a compressione e l’energia di frattura di due tipologie di composito: un intonaco e una malta alle quali sono state aggiunte il 2% sul peso di fibre di bambù della specie Phillostachys iridescens. I risultati ottenuti mostrano un sostanziale miglioramento della duttilità rispetto al materiale senza fibra, con l’insorgere di un ramo duttile in fase post-critica conservando comunque pressoché inalterata la resistenza.
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Carlswärd, Jonas. "Shrinkage cracking of steel fibre reinforced self compacting concrete overlays : test methods and theoretical modelling /." Luleå : Division of Structural Engineering, Luleå University of Technology, 2006. http://epubl.ltu.se/1402-1544/2006/55/LTU-DT-0655-SE.pdf.
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Hedebratt, Jerry. "Industrial Fibre Concrete Floors : Experiences and Tests on Pile-Supported Slab." Doctoral thesis, KTH, Bro- och stålbyggnad, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-102670.
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Pile supported floor slabs have often been designed solely in ultimate limit state ULS and then foremost with uniformly distributed loadings UDL. The investigation of serviceability limit state SLS has been of simpler nature, even according to the governing codes of practice. Often it has been minimum‑reinforced with the presumption that full friction to the supporting ground is present, whit‑out any inspection, which by the Swedish code of practice even more reduced the addition of crack reinforcement. The cracks have not been controlled, before they in fact have occurred. For pile supported floor slabs the ground support will be there still, at least for a time, after the casting. As the ground settles, as dehydration always will occur, and drainage and the covering roof the precipitation to reach the ground, the slab will often be completely free bearing between the piles. The minimum reinforcement is based on the assumption that only the upper layer is needed to reinforce due to dehydration shrinkage – despite that the whole floor section in time will obtain the same moisture profile and also shrinkage magnitude. One often excludes the influence of creep and temperature and the affect from external loading and local variance of restraints in calculations in the SLS. Research on behaviour in SLS has been modest; in spite of that the contractors and the client and finally the end‑user of the floors often suffer from these problems. It has by this thesis been established that the shrinkage of the concrete used for industrial floors is large 0.9‑1.1 ‰, and that the problem foremost arise from cracking and problems with joints and unevenness in the floor. The integrated method for design and production of industrial floors is a way to the solution, but requires that all involved assign to co‑operate to 100 %. Furthermore it is required that one selects the proper materials to the proper design and the proper production method. If one will save cost this will often be on materials; which will lead to reduced reinforcement content and reduced concrete thickness. This way is wrong and will in end make the client suffer economically. A way to solve this has been to cast the floors with steel fibre concrete SFC; from the beginning often a little bit thicker and with moderate steel fibre content and complementary reinforcement, compared to present execution. The competition from abroad has nevertheless shaped solutions that with thinner slabs and less traditional reinforcement and invalid design calculations compete on faulty grounds. This work demonstrates how this make the floor suffer in ULS and SLS. Trough full‑scale testing (half of a normally loaded industrial floor in matter of geometry) where a pile supported floor slab has been simulated by a flat‑slab floor cast in steel fibre concrete, it has been shown that the solution with steel fibre concrete performs well in slabs for industrial floors. On one hand it gives the opportunity to production wise superior methods for placing concrete which potentially could gain the environment with reduced reinforcement content, and on the other hand SFC brings a ductile failure behaviour for loadings with much larger magnitudes than in normal ULS design, and further SFC provides with a stiffer response and with possibility to construct slabs with small creep deformation. Finally it has been established that, when it comes to short‑term point loadings (ULS) and with long-term point loadings (SLS) one can rely on the bearing capacity and the tough behaviour of SFC. And that one may exert an influence on both limit states, through variation of the SFC and the reinforcement content. This is shown for a real bearing structure, the pile supported industrial floor, and that in a safe way.QC 20120921
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Jeffery, D. R. N. "Test of a GS1 scintillating optical fibre vertex detector with a reticon RA256 photodiode array readout." Thesis, University of Bristol, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381373.
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Odendaal, Courtney Megan. "Establishment of performance-based specifications for the structural use of locally available macro-synthetic fibres." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/96678.
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Thesis (MEng)--Stellenbosch University, 2015.ENGLISH ABSTRACT: FRC (Fibre-reinforced concrete) has become a common form of secondary and even primary reinforcing in some applications throughout the world. In South Africa, the structural applications are limited primarily to steel fibres while cheaper, lighter and more durable synthetic fibres have been side-lined due to low stiffnesses. The purpose of this research project is to investigate the behaviour of synthetic fibre-reinforced concrete (SynFRC) using fibres which are locally available in South Africa, and to propose a performance-based specification and test method for the use of these fibres. In order to achieve this, single fibre pull-out tests were performed on four locally available polypropylene fibres. It was found that the average bond stresses of the fibres are influenced primarily by the fibre cross sectional shape, longitudinal geometry and surface treatment, and secondarily by the aspect ratio. The W/C ratio had little effect on the single fibre performance of non-treated fibres, but appeared to have a slight effect on the single fibre performance of the surface treated fibre. From the experimental results, the highest fibre bond stress will be generated by using a fibre with an X-shaped cross section, longitudinal crimping and applying a surface treatment to this fibre. It also appears that the bond stress distribution for flat fibres is close to uniform, while the bond stress distribution for non-flat crimped fibres has a high mechanical interlock component at the surface end. Macro-mechanical performance tests were performed by means of the BS EN 14651 (2007) three point beam bending test and the ASTM C1550 (2012) Round Determinate Panel Test (RDPT). These tests were selected following a thorough literature review. The RDPT was found to be more consistent and able to identify trends which the three point beam bending test could not. In addition, the three point beam bending test’s most popular output, the Re,3 value tended to be misleading with varying W/C ratios, and it is recommended that the equivalent flexural tensile strength be used instead if the three point beam bending test is used. The macro-mechanical testing showed that increasing the fibre dosage did increase post-cracking performance. The flat fibres’ performance was significantly better than that of the non-flat fibres, and also increased at a faster rate with increasing fibre dosage. The post-cracking performance decreased with increasing W/C ratios and increasing aggregate sizes. The macro-mechanical performance was inversely proportionate to the single fibre performance. The macro-mechanical performance decreased with increasing fibre bond stress, and increased with increasing equivalent diameter, which equates to fewer fibres in a set volume of fibres. Finally, basic principles were developed from the data. These principles were used to predict the RDPT and three point beam bending test performance parameters based on fibre dosage, single fibre properties (bond stress and equivalent diameter), W/C ratio and aggregate size from the available data. The principles can be further refined with more experimental data.
AFRIKAANSE OPSOMMING: Vesel-gewapende beton word regoor die wêreld as ’n algemene vorm van sekondêre en selfs primêre versterking gebruik. In Suid-Afrika is die strukturele toepassings hoofsaaklik tot staal vesels beperk, terwyl goedkoper, ligter en meer duursame sintetiese vesels vermy word as gevolg van lae styfhede. Die doel van hierdie navorsingsprojek is om die gedrag van sintetiese-veselversterktebeton (SynFRC) te ondersoek deur gebruik te maak van vesels wat in Suid-Afrika beskikbaar is, en 'n prestasie-gebaseerdespesifikasie en toetsmetode vir die gebruik van sintetiese vesels voor te stel. Enkelveseluittrektoetse is op vier plaaslik beskikbare polipropileen vesels uitgevoer. Daar is gevind dat die gemiddelde verbandspanning van die vesel hoofsaaklik deur die vesel deursnee vorm, lengte meetkunde en oppervlak behandeling beïnvloed word, en tweedens deur die aspek verhouding beïnvloed. Die W/C-verhouding het min effek op die enkelveselprestasie van nie-behandelde vesels, maar het 'n effek op die enkeleveselprestasie van die oppervlak-behandelde vesel gehad. Die eksperimentele resultate wys dat die hoogste vesel verbandspanning deur 'n vesel met 'n X-vormige deursnit, lengte krimping en toepassing van 'n oppervlak behandeling gegenereer sal word. Dit blyk ook dat die verbandspanningverspreiding vir ’n plat vesel naby aan uniform is, terwyl die verbandspanningverspreiding vir ’n nie-plat gekrimpde vesel 'n hoë meganiese grendeling komponent op die oppervlak ente het. Makro-meganiese prestasietoetse is uitgevoer deur middel van die BS EN 14651 (2007) driepuntbalkbuigtoets en die ASTM C1550 (2012) RDPT. Hierdie toetse is ná ’n deeglike literatuuroorsig gekies. Die RDPT is meer konsekwent en is in staat om neigings te identifiseer wat die driepuntbalkbuigingtoets nie kan nie. Daarbenewens, met wisselende W/C verhoudings, is die driepuntbalkbuigtoets se gewildste resultaat, die Re,3-waarde geneig om misleidend te wees. Dit word aanbeveel dat die ekwivalentebuigtreksterkte in plaas van die Re,3-waarde as die drie punt balk buig toets resultaat gebruik word. Die makro-meganiesetoets het getoon dat die verhoging van die veseldosis ’n toename in na-krakingprestasie veroorsaak. Die plat vesels se prestasie was aansienlik beter as die van nie-plat vesels, en het met 'n toenemende veseldosis teen 'n vinniger koers verhoog. Die na-krakingprestasie het met toenemende W/C en die verhoging van die klip grootte afgeneem. Die makro-meganieseprestasie was omgekeerd eweredig aan die enkelveselprestasie. Die makro-meganieseprestasie het met toenemende vesel band stres verminder, en het met 'n toenemende gelykstaande deursnee (wat gelykstaande is aan minder vesel in 'n stel volume van vesel) vergroot. Ten slotte is basiese beginsels uit die data ontwikkel. Hierdie beginsels is gebruik om die RDPT en driepuntbalkbuigtoets prestasieparameters gebaseer op veseldosis, enkelveseleienskappe (verbandspanning en ekwivalentediameter), W/C-verhouding en klip grootte van die beskikbare data te voorspel. Die beginsels kan met meer eksperimentele data verder verfyn word.
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Qsymah, Ansam. "In-situ X-ray computed tomography tests and numerical modelling of ultra high performance fibre reinforced concrete." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/insitu-xray-computed-tomography-tests-and-numerical-modelling-of-ultra-high-performance-fibre-reinforced-concrete(7c27ef36-afc8-4ea7-8c72-7d92eba924f9).html.
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Ultra high performance fibre reinforced concrete (UHPFRC) is a relatively new fibre reinforced cementitious composite and has become very popular in construction applications. Extensive experimental studies have been conducted, demonstrating its superior properties such as much higher strength, ductility and durability than conventional fibre reinforced concrete (FRC) and high performance concrete. However, the material's damage and fracture mechanisms at meso/micro scales are not well understood, limiting its wider applications considerably. This study aims at an in-depth understanding of the damage and fracture mechanisms of UHPFRC, combining microscale in-situ X-ray computed tomography (µXCT) experiments and mesoscale image-based numerical modelling. Firstly, in-situ µXCT tests of small-sized UHPFRC specimens under wedge splitting loading were carried out, probably for the first time in the world, using an in-house designed loading rig. With a voxel resolution of 16.9µm, the complicated fracture mechanisms are clearly visualised and characterised using both 2D images and 3D volumes at progressive loading stages, such as initiating of micro-cracks, arresting of cracks by fibres, bending and pulling out of fibres and spalling of mortar at the exit points of inclined fibres. Secondly, based on the statistics of pores in the µXCT images obtained for a 20mm cube specimen, an efficient two-scale analytical-numerical homogenisation method was developed to predict the effective elastic properties of the UHPFRC. The large number of small pores were first homogenised at microscale with sand and cement paste, using elastic moduli from micro-indentation tests. 3D mesoscale finite element models were built at the second scale by direct conversion of the µXCT images, with fibres and large pores were faithfully represented. The effects of the volume fraction and the orientation of steel fibres on the elastic modulus were investigated, indicating that this method can be used to optimise the material micro-structure. Thirdly, 3D mesoscale finite element models were built for the specimen used in the in-situ µXCT wedge splitting test, with embedded fibre elements directly converted from the µXCT images. The fracture behaviour in the mortar was simulated by the damage plasticity model available in ABAQUS. Finally, 2D mesoscale finite element models were developed to simulate the fracture behaviour of UHPFRC using cohesive interface elements to simulate cracks in the mortar, and randomly distributed two-noded 1D fibres and connector elements to simulate the pull-out behaviour of fibres. This approach offers a link between the fibres pull-out behaviour and the response of the whole composite at the macroscale, thus it can be used to conduct parametric studies to optimise the material properties.
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Versari, Carlo. "Caratterizzazione avanzata di conglomerati speciali prodotti con leganti polimerici trasparenti e fibre di rinforzo diffuse." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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Al giorno d’oggi la progettazione di una pavimentazione stradale è focalizzata verso soluzioni innovative che fanno riferimento ad una nuova scuola di pensiero dove oltre agli aspetti tecnici e prestazionali vengano considerati quelli legati alla salvaguardia ambientale e alla mitigazione dell’impatto di una infrastruttura sull’ambiente circostante. Il presente lavoro di tesi va inquadrato in quest’ottica, avendo in oggetto la caratterizzazione di un legante innovativo utilizzato per la realizzazione di conglomerati ad uso stradale, e la valutazione del potenziale incremento delle sue proprietà meccaniche tramite l’aggiunta di fibra di rinforzo.
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Morisset, Adèle. "Interaction laser-silicium et transport fibré pour le test de circuits intégrés par stimulation photoélectrique non-linéaire." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00920339.
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Cette thèse est consacrée à l'étude des mécanismes d'interaction laser-matière en régime femtoseconde pour l'analyse de circuits intégrés par stimulation photoélectrique non-linéaire. Cette technique permet d'accroitre la résolution pour répondre à la miniaturisation des composants électroniques. Les milieux étudiés dans ce travail sont plus particulièrement le silicium, matériau constitutif des circuits intégrés, et la silice pour le transport des impulsions laser dans une fibre optique. En effet, l'émergence de cette technique d'analyse en milieu industriel requiert l'utilisation de systèmes compacts, fiables et sécuritaires. Les simulations réalisées montrent la génération de charges dans le silicium et la propagation des impulsions dans des fibres photoniques à cœur creux identifiées pour limiter les effets non-linéaires. Des expérimentations sur composants permettent de les confronter aux simulations et de valider l'utilisation de ce type de fibres.Enfin, ce travail a permis de déterminer les paramètres optiques et laser essentiels ainsi que les technologies compatibles avec les contraintes industrielles en analyse de circuits intégrés.
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Saad, Suleiman S. E. "Mechanical behaviour of fibre reinforced unsaturated clay : this investigation is to determine the improvement in the mechanical behaviour of unsaturated clayey soil after inclusion of carpet fibre waste." Thesis, University of Bradford, 2016. http://hdl.handle.net/10454/14585.
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To acquire deeper understanding and insights into the mechanical behaviour of fibre reinforced saturated/unsaturated cohesive soils, a programme of work was designed and included. 1) Conducting standard Consolidation Undrained (CU) tests to investigate mechanical behaviour of non-reinforced fully saturated soil. 2) Studying the strength of fibre reinforced clay though unconfined compression tests. 3) Testing the behaviour of unsaturated reinforced soil in unsaturated triaxial tests. 4) Determining the soil-water characteristic curves (SWCC) on soil sample with different fibre content. The investigation was undertaken on a clay of low plasticity index. Samples tested with addition of 1, 3 and 5 % fibre content and different values of matric suction of 50, 100 and 200 kPa, one of the challenges that were encountered in this research are how to prepare homogenous samples. A method for prepared compacted fibre reinforced soils with improved fibre distribution and density profile has been proposed and examined. The test results indicated that waste carpet fibres increase the shear strength of unsaturated clay soils. It was also found that relative increase in strength is also a function of applied suction. An increase in waste carpet fibres was found to reduce the hysteresis of soil. A data analysis conducted on the results of unsaturated tests as a function of fibre content and matric suction. The behaviour modelled was shown to be a perfect fit with the experimental data.
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Venugopal, Saranya. "Synthesis and processing of sub-micron hafnium diboride powders and carbon-fibre hafnium diboride composite." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12532.
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A vehicle flying at hypersonic speeds, i.e. at speeds greater than Mach 4, needs to be able to withstand the heat arising from friction and shock waves, which can reach temperatures of up to 3000oC. The current project focuses on producing thermal protection systems based on ultra high temperature ceramic (UHTC) impregnated carbon-carbon composites. The carbon fibres offer low mass and excellent resistance to thermal shock; their vulnerability is to oxidation above 500oC. The aim of introducing HfB2, a UHTC, as a coating on the fibre tows or as particulate reinforcement into the carbon fibre preform, was to improve this property. The objectives of this project were to: i) identify a low temperature synthesis route for group IV diborides, ii) produce a powder fine enough to reduce the difficulties associated with sintering the refractory diborides, iii) develop sol-gel coating of HfB2 onto carbon fibre tows iv) improve the solid loading of the particulate reinforcement into the carbon fibre preform, which should, in turn, increase the oxidation protection. In order to achieve the above set objectives, fine HfB2 powder was synthesized through a low temperature sol gel and boro/carbothermal reduction process, using a range of different carbon sources. Study of the formation mechanism of HfB2 revealed an intermediate boron sub-oxide and/or active boron formation that yielded HfB2 formation at 1300oC. At higher temperatures the formation of HfB2 could be via intermediate HfC formation and/or B4C formation. Growth mechanism analysis showed that the nucleated particles possessed screw dislocations which indicated that the formation of HfB2 was not only through a substitution reaction, but there could have been an element of a precipitation nucleation mechanism that lead to anisotropic growth under certain conditions. The effect of carbon sources during the boro/carbothermal reduction reaction on the size of the final HfB2 powders was analysed and it was found that a direct relation existed between the size and level of agglomeration of the carbon sources and the resulting HfB2 powders. A powder phenolic resin source led to the finest powder, with particle sizes in the range 30 to 150 nm. SPS sintering of the powder revealed that 99% theoretical density could be achieved without the need for sintering aids at 2200oC. Sol-gel coatings and slurry impregnation of HfB2 on carbon fibres tows was performed using dip coating and a 'squeeze-tube' method respectively. Crack free coatings and non-porous matrix infiltration were successfully achieved. The solid loading of the fine HfB2 into the carbon fibre preform was carried out through impregnation of a HfB2 / phenolic resin/acetone slurry using vacuum impregnation. Although the sub-micron Loughborough (LU) powders were expected to improve the solid loading, compared to the commercially available micron sized powders, due to the slurry made from them having a higher viscosity because of the fine particle size, the solids loading achieved was consequently decreased. Optimisation of the rheology of the slurry with LU HfB2 still requires more work. A comparison of the oxidation and ablation resistance of the Cf-HfB2 composites prepared with both commercial micron sized HfB2 powder and Loughborough sub-micron sized HfB2 powder, each with similar level of solid loading, was carried out using oxyacetylene torch testing. It was found that the composite containing the finer, Loughborough powders suffered a larger erosion volume than the composite with the coarser commercial powders indicating that the former offered worse ablation and oxidation resistance than the latter. A full investigation of the effect of solids loading and particle size, including the option of using mixtures of fine and coarse powders, is still required.
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Rodovalho, Tainá Gomes. "Medição da velocidade da onda ultrassônica longitudinal em compósitos de fibra de carbono/epóxi." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264068.
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Orientador: Auteliano Antunes dos Santos JúniorDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: O uso dos materiais compósitos pela indústria aeronáutica tem ganhado cada vez mais espaço, sendo, portanto, de grande importância o conhecimento de suas características tanto na fase de projeto quanto na de manutenção. A presença de falhas e tensões não identificadas durante o processo de fabricação ou de manutenção pode significar perdas sociais, ambientais e econômicas. Dentre os métodos de medição e de inspeção não destrutiva em compósitos, os ultrassônicos mostraram-se mais eficientes por não depender da estrutura cristalina do material como os métodos de difração de nêutrons e de raios-X. Assim, determinar o perfil de resposta da velocidade de propagação da onda ultrassônica longitudinal criticamente refratada (LCR) em função da tensão aplicada para esse material, e avaliar se esta é linear e replicável, torna-se uma tarefa importante para posterior análise de tensões residuais. Neste trabalho analisa-se as influências da direção das fibras e da temperatura na velocidade de propagação das ondas ultrassônicas longitudinais, visando avaliar, posteriormente, o perfil acustoelástico dos laminados unidirecionais carbono/epóxi (HexTow® AS4 /Hexply® 8552) com direções de fibra a 0º, 45º e 90º. Para analisar os fatores de influência foram executados os testes de análise da variância (ANOVA) com distribuição F e o teste de Tukey, para comparar os níveis dos fatores. Os resultados mostraram que todos os fatores analisados influenciam na medida da velocidade da onda longitudinal, sendo a direção das fibras o fator de maior influência. Os resultados obtidos permitirão, em trabalhos futuros, a construção de modelo que permita obter a resposta de laminados quasi - isotrópicos empregados na indústria aeronáutica para diferentes sequências de empilhamento
Abstract: The use of composite materials for aerospace industry has gained more space and is therefore of great importance the knowledge of its characteristics, both in the design and in the maintenance. The presence of faults and unidentified strains during manufacturing or maintenance process can mean social, environmental and economic losses. Within the methods of measurement and nondestructive inspection of composites, ultrasonic methods have shown to be more efficient because they do not depend on the crystal structure of the material as the methods of neutron diffraction and X-rays. Thus, determining the response profile of the propagation velocity of longitudinal critically refracted (LCR) waves as a function of stress applied to the material, and to evaluate whether this is linear and repeatable, has become an important task for later analysis of residual stresses. This study analyzes the influences of fiber direction and temperature on the speed of propagation of longitudinal ultrasound waves, to evaluate further the profile acustoelastics of laminated unidirectional carbon/ epoxy (HexTow ® AS4 / Hexply ® 8552) with directions fiber at 0 °, 45 and 90. To analyze the factors of influence were performed the analysis of variance (ANOVA) test with distribution F and Tukey's test to compare the levels of factor. The results showed that all analyzed factors influences in the measure of longitudinal wave velocity, being the direction of the fibers the factor of most influence. The results allow the construction of a model, in future works, to achieve the response of laminated quasi - isotropic employed in the aviation industry for different stacking sequences
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestra em Engenharia Mecânica
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Paladino, Mattia. "Test su un prototipo di rivelatore per la misura di sezione d’urto del neutrino elettronico." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16826/.
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Il neutrino è una particella fondamentale del Modello Standard, è stata scoperta nel 1956 e col passare degli anni si venne a conoscenza del fatto che questi sono caratterizzati da una rispettiva antiparticella e da tre tipi di sapore. La fisica dei neutrini è tuttavia ancora ricca di incomprensioni: molte delle proprietà che descrivono queste particelle risultano ancora sconosciute.
Il progetto ENUBET propone un’iniziativa con lo scopo di far luce su alcuni dei misteri che circondano le nostre conoscenze sui neutrini e sarà il protagonista di questo elaborato.
Nel primo capitolo si farà un’introduzione sulla scoperta dei neutrini e sulle proprietà che li descrivono.
Nel secondo capitolo, si introdurranno gli scopi del progetto ENUBET e verrà descritto il modo in cui questo progetto ha intenzione di approcciarsi alle problematiche legate alle incertezze sul flusso ed alla misura della sezione d’urto; inoltre si discuterà delle tecniche adottate dal progetto per raggiungere i propri obiettivi.
Nel terzo capitolo verrà descritta l’attività di laboratorio da me svolta presso la sede dell’INFN di Bologna, nella quale ho assistito alla costruzione di un prototipo di calorimetro destinato ad essere sottoposto ad un test beam presso il CERN di Ginevra.
Successivamente verrà discussa l’analisi dei dati prodotti dal suddetto test ed elaborati attraverso l’utilizzo del software ROOT.
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Corrêa, Lúcio de Abreu. "Estudo de propagação de ondas em tubos epóxi reforçado com fibra de vidro." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/96306.
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A adoção de materiais compósitos pela indústria de petróleo e gás vem ocorrendo de forma gradual, e ainda encontra certa resistência devido à novidade de sua aplicação em projetos mecânicos do setor, e da menor confiabilidade que possuem em relação a metais. A sua implementação em maiores escalas depende também do desenvolvimento de métodos de inspeção e monitoramento de integridade estrutural. Em paralelo a isso, sistemas de varredura de tubulações baseados em ondas guiadas ultrassônicas vêm ganhando espaço devido à sua capacidade de inspecionar toda a seção de trechos extensos de uma tubulação metálica. Baseado nestas duas premissas, este trabalho tem como objetivo apresentar estudos visando o desenvolvimento de uma metodologia que seja capaz de obter as propriedades elásticas de um meio e obter as características de propagação das ondas mecânicas, cobrindo uma metodologia para obtenção das propriedades elásticas baseados em ensaios ultrassônicos, um método de otimização baseado em propriedades vibracionais e por fim, confrontando dados provenientes de modelos em elementos finitos com resultados experimentais e aproximações teóricas. Como resultados espera-se gerar informações necessárias para que possa-se compreender os mecanismo de propagação das ondas elásticas, pois é ele que permitirá a obtenção de informações a respeito dos defeitos presentes na estrutura analisada ou ainda utilizar as informações de dispersão em função da frequência e em função da direção para localização de fontes acústicas em meios ortotrópicos, sendo o conhecimento das propriedades de fase e energia das ondas em tais materiais de fundamental importância para a plena exploração do seu potencial de inspeção e monitoramento.The adoption of new materials by the oil and gas industry has been occurring gradually and still finds some resistance due to the novelty of their application in mechanical design and their lower reliability compared to metals. The usage in large scales also depends on the development of inspection methods and structure health monitoring. In a parallel way, systems that scan pipes using mechanical guided waves have gained space because of their ability to inspect the section of large excerpts of an metallic pipe. Based on these two assumptions, this work aims to study the development of a methodology that is able to obtain the elastic properties of a medium and obtain mechanical characteristics through propagation of the stress waves in it. For this, a method to obtain elastic properties based on ultrasonic testing, a optimization method was based on vibrational properties, and comparison of to data from finite element models with experimental results and theoretical approaches were used. The results are expected to generate information needed for understand the mechanism of propagation of elastic waves, needed to obtain information about defects present in the structure or using information of angular or frequency dispersion for localizing acoustic sources in orthotropic media. As knowledge of the properties of the phase and energy waves propagation in such material are crucial for the full exploitation of inspection and monitoring.
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Santos, Ana Paula Silva dos. "Estudo do comportamento de misturas solo-cimento-fibra sob altas pressões." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2008. http://hdl.handle.net/10183/163955.
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Os ensaios em solos sob altas pressões tiveram seu interesse renovado nos últimos anos em parte devido a trabalhos que anseiam por uma investigação mais profunda da mecânica dos solos fundamental a altas pressões para aplicação de modelos constitutivos em solos granulares. Para desenvolvimento desses modelos é necessária uma completa compreensão do comportamento volumétrico dos solos, assim como a aplicação da teoria do estado crítico aos mesmos, o que requer ensaios em níveis de tensões que são ordens de magnitude maiores que os aplicados na maioria das estruturas de engenharia no caso de solos arenosos. Este trabalho estudou o comportamento mecânico de materiais compósitos constituídos a partir da utilização de um solo arenoso, cimento Portland CP-V e fibras de polipropileno sob altas pressões. O solo utilizado foi uma areia fina de granulometria uniforme extraída de uma jazida localizada no município de Osório - RS. Ensaios de compressão isotrópica sob altas pressões foram realizados em amostras de areia, areia-fibra, areia-cimento e areia-cimentofibra, em uma variedade de volumes específicos iniciais. Os resultados indicaram mudanças no comportamento do material não reforçado devido à inclusão de fibras e/ou cimento. Foram observadas linhas de compressão normal distintas e paralelas para cada mistura. Os comprimentos das fibras, medidos após a aplicação de altas tensões, mostraram que algumas fibras sofreram quebra e outras extensão, indicando que as fibras trabalham em compressão isotrópica. Um aumento do modulo volumétrico devido à presença de ambos: fibras e cimento foi observado. Uma redução na quebra das partículas devido à presença de fibras também foi observada. Para o estudo do estado crítico, ensaios triaxiais isotropicamente consolidados drenados levados a deformações cisalhantes de até 40% foram realizados. As envoltórias de estado crítico dos materiais reforçados no plano p': q apresentaram-se bi-lineares. As linhas de estado crítico no plano v:lnp' para a areia com e sem reforço mostraram-se inicialmente distintas e curvilíneas certo nível de tensões, a partir do qual convergiram para uma única LEC. O material cimentado apresentou o mesmo comportamento do material não cimentado no estado crítico, assim como o material cimentado reforçado em relação ao solo reforçado sem cimentação. Mesmo a tensões confinantes baixas as fibras apresentaram alongamento e ruptura para o nível de deformações cisalhantes atingidas. O aumento da tensão de confinamento ocasionou progressiva ruptura das fibras e a perda gradual da sua atuação benéfica sobre o comportamento do solo. A cimentação pode aumentar a eficiência deste sistema melhorando o ancoramento das fibras, permitindo que as fibras atuem mais efetivamente na matriz, ao menos para as tensões mais baixas.Nowadays the interest in soil testing under high stresses has been renewed dueto the greater depths reached by foundation structures as well as the need of a better understanding of fundamental soil behaviour and its application in soil models for granular materiais. To develop these models it is necessary a complete understanding of the volumetric behaviour of soils and the application of Critical State theory, which for granular materiais require triaxial tests at stresses much higher than those typical on the majority of the engineering structures. This work studied the mechanical behaviour of composite materiais, using sand, Portland cement CP-V and polypropylene fibres, under high stresses. The soil used in this study is an uniform fine sand extracted from a quarry in Osório - RS. High stress isotropic triaxial tests were undertaken in samples of sand, sand-fibre, sand-cement and sand-cement-fibre in a variety of initial specific volumes. Comparison between the test results indicated changes on the behaviour of the un-reinforced material due to the inclusion of fibres and/or cement. Distinct and parallel normal compression lines were observed for every mixture. The fibre lengths, measured after high pressure application, have shown that some fibres suffered an elongation and others were broken, indicating that fibres work in tension under isotropic compression. An increase in bulk modulus was observed in the presence of both: fibres and cement. Reduced amounts of particle breakage were also found in the mixtures containing fibres. To better determine critical state the samples were sheared up to 40% of shear deformation after the isotropic consolidation took place. The critical state envelopes of the reinforced materials, in the stress space p': q, have shown a bi-linear behaviour. The critical state line in the space v:lnp' for the sand and reinforced sand was distinct and curved and converged to a stress threshold, becoming linear and unique. On the critical state the cemented material have shown the same behaviour as the uncemented soil. The same happened to the cemented reinforced material related to the reinforced soil. It can be seen that even at small stresses the fibres present elongation and rupture after reaching high strains. The increase in confining stress led to a progressive rupture ofthe fibres anda gradual loss of the benefit of having fibres mixed in the soil. Cementation can increase the efficiency of the system, improving the bonding between fibres and soil particles, this allow the fibres to be more effective in the soil matrix, at least at low stress levels.
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Magnani, Marco. "Effect of fibre damage on compressive strength of CFRP laminates." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/22322/.
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This work investigates the effects of fibre damage on compressive strength of CFRP laminates under compressive loading. To characterise the influence of fibre failure, parameters such as the length and depth of the damaged region are considered. 3D Finite Element models are created to reproduce the artificially damaged laminates and gain an initial understanding of how fibre damage may affect the specimens. Secondly, coupons are manufactured and tested in compression following ASTM D 7137. DIC equipment is employed to better visualise the behaviour of the loaded components and gain insight on the effects of the different damage configurations. The results show that although fibre damage reduces the compressive strength of the tested components, the configuration of such damage has little influence. Interestingly, damage configuration seems to play a pivotal role on the development of delamination and kinks at final failure.
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Wang, Ning. "Electrospun membranes for implantable glucose biosensors." Thesis, Brunel University, 2012. http://bura.brunel.ac.uk/handle/2438/8718.
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The goal for this thesis was to apply electrospun biomimetic coatings on implantable glucose biosensors and test their efficacy as mass-transport limiting and tissue engineering membranes, with special focus on achieving reliable and long sensing life-time for biosensors when implanted in the body. The 3D structure of electrospun membranes provides the unique combination of extensively interconnected pores, large pore volumes and mechanical strength, which are anticipated to improving sensor sensitivity. Their structure also mimics the 3D architecture of natural extracellular matrix (ECM), which is exploited to engineer tissue responses to implants. A versatile vertical electrospinning setup was built in our workshop and used to electrospin single polymer - Selectophore™ polyurethane (PU) and two polymer (coaxial) – PU and gelatin (Ge) fibre membranes. Extensive studies involving optimization of electrospinning parameters (namely solvents, polymer solution concentration, applied electric potential, polymer solution feed flow rate, distance between spinneret and collector) were carried out to obtain electrospun membranes having tailorable fibre diameters, pore sizes and thickness. The morphology (scanning electron microscopy (SEM) and optical microscopy), fibre diameter (SEM), porosity (bubble point and gravimetry methods), hydrophilicity (contact angle), solute diffusion (biodialyzer) and uniaxial mechanical properties (tensile tester) were used to characterize certain shortlisted electrospun membranes. Static and dynamic collector configurations for electrospinning fibres directly on sensor surface were optimized of which the dynamic collections system helped achieve snugly fit membranes of uniform thickness on the entire surface of the sensor. The biocompatibility and the in vivo functional efficacy of electrospun membranes off and on glucose biosensors were evaluated in rat subcutaneous implantation model. Linear increase in thickness of electrospun membranes with increasing electrospinning time was observed. Further, the smaller the fibre diameter, smaller was the pore size and higher was the fibre density (predicted), the hydrophilicity and the mechanical strength. Very thin membranes showed zero-order (Fickian diffusion exponent ‘n’ ~ 1) permeability for glucose transport. Increasing membrane thickness lowered ‘n’ value through non-Fickian towards Fickian (‘n’ = 0.5) diffusion. Thin electrospun PU membranes (~10 μm thick) did not affect, while thicknesses between 20 and 140 μm all decreased sensitivity of glucose biosensor by about 20%. PU core - Ge shell coaxial fibre membranes caused decrease in ex vivo sensitivity by up to 40%. The membranes with sub-micron to micron sized pore sizes functioned as mass-transport limiting membranes; but were not permeable to host cells when implanted in the body. However, PU-Ge coaxial fibre membranes, having <2 μm pore sizes, were infiltrated with fibroblasts and deposition of collagen in their pores. Such tissue response prevented the formation of dense fibrous capsule around the implants, which helped improve the in vivo sensor sensitivity. To conclude, this study demonstrated that electrospun membrane having tailorable fibre diameters, porosity and thickness, while having mechanical strength similar to the natural soft tissues can be spun directly on sensor surfaces. The membranes can function as mass-transport limiting membranes, while causing minimal or no effect on sensor sensitivity. With the added bioactive Ge surfaces, evidence from this study indicates that reliable long-term in vivo sensor function can be achieved.
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Rajendran, Vijayalakshmi. "Development of Organ-Specific Progenitor Cell Cultures as Efficacy Test Platforms for Electron-Spun Fibre Meshes in Regenerative Medicine Applications." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-74232.
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The nervous and cardiovascular system plays the most complex and vital role in all organisms. Any damage or injury to these essential organs in our body results in long term irreversible impairment or death. The main goal of the regenerative medicine is to repair or recreate tissues using stem cells to restore the vital function of the targeted organ. Along with organ specific stem/progenitor cells, non-toxic, biodegradable synthetic polymers are also needed for an effective reparative therapy. The effect of PCL materials and surface modified (PEDOT coated) PCL materials of different topology with neural progenitor cells as test platforms are evaluated for cytotoxicity and neuron differentiation. The stem cells from heart are isolated and characterized as cardiac stem cells by Fluorescence activated cell sorting through specific antigen expression. The cardiac stem cells are used to establish effective proliferation and differentiation system. Hence, developing cardiac and neural progenitor cell cultures as an efficacy test platforms for biomaterials of different diameter and orientation benefits respective tissue engineering with proper restoration of function. Further, the nerve and cardiac tissue rejuvenation would serve as a regenerative therapy for numerous neurodegenerative disorders and cardiovascular disorders like myocardial infarction respectively.
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Fogno, Ouambo Baudelaire. "Optimisation d'un banc de test amplifié à 10 Gb/s pour l'étude des technologies avancées de transmission par fibre optique." Mémoire, École de technologie supérieure, 2008. http://espace.etsmtl.ca/97/1/FOGNO_OUAMBO_Baudelaire.pdf.
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La réalisation d'un banc de test est essentielle dans la recherche et le développement des
réseaux de communication par fibre optique. Le banc de test permet de valider les
concepts théoriques associés à la modélisation des systèmes de transmission et réseaux
optiques. Les concepts théoriques se valident par le biais des simulations et tests réels
réalisés sur des liaisons optiques typiques des réseaux optiques métropolitaines et
longues portées déployées sur le terrain. Une analyse théorique de la liaison point à point
a été effectuée à l'aide du logiciel de simulation VPI. La liaison optique point à point
(linéaire) a été réalisée en laboratoire afin de valider et optimiser les résultats de
simulations. La liaison optique point à point se configure en boucle de recirculation par
l'ajout des modules de commutation et de contrôle du signal. Le banc de test configuré
en boucle de recirculation a été caractérisé en calculant la portée maximum du système
telle que déterminée par les limites d'atténuation, de dispersion et des effets non
linéaires. La performance du banc de test a été mesurée à l'aide du diagramme de l'oeil.
Nous avons pu parcourir 1800 km avec un signal optique dont le débit est de 10 gigabits
par seconde.
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Fogno, Ouambo Baudelaire. "Optimisation d'un banc de test amplifié à 10 Gb/s pour l'étude des technologies avancées de transmission par fibre optique /." Thèse, Montréal : École de technologie supérieure, 2008. http://proquest.umi.com/pqdweb?did=1459924941&sid=4&Fmt=2&clientId=46962&RQT=309&VName=PQD.
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Thèse (M. Ing.) -- École de technologie supérieure, Montréal, 2008."Mémoire présenté à l'École de technologie supérieure comme exigence partielle à l'obtention de la maîtrise en génie électrique." "par Fogno Ouambo, Baudelaire" -- p. de t. CaQMUQET CaQMUQET Bibliogr. : f. [124]-128. Également disponible en version électronique. CaQMUQET
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Farina, Ana Paula. "Estudo ex vivo da resistência de união de pinos de fibra às paredes do canal radicular utilizando diferentes cimentos." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/58/58131/tde-19022009-163351/.
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O objetivo deste estudo foi avaliar ex vivo a resistência de união de pinos de fibra de vidro (FV) e pinos de fibra de carbono (FC) nos terços cervical, médio e apical do canal radicular, cimentados com dois tipos de cimentos resinosos: auto-adesivo (RX) e convencionais (CP). Quarenta caninos superiores foram separados em 4 grupos (n = 10) de acordo com o cimento e pino utilizado. Após a secção transversal dos dentes em fatias de 2mm de espessura, o teste de resistência adesiva (0,5mm/min) foi realizado nos terços cervical, médio e apical de cada espécime. Cinco espécimes de cada grupo foram analisados em microscopia eletrônica de varredura para observar o tipo de fratura. Os dados foram submetidos à 2-way ANOVA (Bonferroni, p< 0,05). Os resultados mostraram que os pinos de FV apresentaram os maiores valores de resistência adesiva, tanto cimentados com RX quanto com CP. Analisando especificamente o tipo de cimento, pinos cimentados com RX (FV e FC) apresentaram maiores valores de resistência adesiva (p<0,05) que CP. Para todos os grupos em estudo, a resistência de união foi maior no terço cervical, seguido pelo terço médio e apical. A análise de fratura mostrou predominância de fratura coesiva de pino para RX, sendo que para os pinos cimentados com CP houve predominância de fratura adesiva entre dentina/cimento e mista. Pode-se concluir que a resistência de união foi significativamente afetada pelo tipo de pino e também pelo tipo de cimento utilizado, sendo que os mais altos valores de resistência de união foram encontrados com a utilização de pinos de FV e cimento RX.The objective of this study was to evaluate ex vivo the Bond strength of glass-fiber posts (GF) and carbon-fiber posts (CF) to cervical, medium, and apical thirds of root canals after luting with two types of resinous cements: Self-adhesive (RX) and conventional (CP). Forty maxillary canines were divided into 4 groups (n=10) according to the luting cement and fiber post used. After roots were perpendicularly sectioned in 2mm-thick slices, bond strength teste (0.5mm/min) were perform in coronal, midlle and apical thirds. Five specimens were selected from each group for analysis in Scanning Electron Microscopy to observe the type of fracture. The data were analyzed by 2-way ANOVA (Bonferonis test, p<0.05). The results showed that highest bond strength values to GF, for both luting cements (RX and CP). Regard the type of luting cement, posts (GF and CF) luting with RX had the best performance (p<0.05) that CP. For all groups, bond strength values were higher at cervical third, followed by midlle and apical thirds. The failure analysis demonstrated a predominance of post-cohesive failure for RX, and dentin-adhesive-cement and mixed failure for CP. It was concluded that bond strength was affected by the type of fiber post and type of luting cement, where the highest bond strength values were showed by GF-post and RX-luting cement.
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Tazaly, Zeinab. "Punching Shear Capacity of Fibre Reinforced Concrete Slabs with Conventional Reinforcement : Computational analysis of punching models." Thesis, KTH, Bro- och stålbyggnad, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118825.
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Steel fibre reinforced concrete is not a novel concept, it has been around since the mid-1900s, but despite its great success in shotcrete-reinforced rock walls and industrial floors it has not made any impact on either beams or elevated slab. Apparently, the absence of standards is the main reason. However, the combination of steel fibre reinforced concrete and conventional reinforcement has in many researches shown to emphasize good bearing capacrty. In this thesis, two punching shear capacity models have been analysed and adapted on 136 test slabs perfomred by previous researchers. The first punching model altemative is proposed in DAfStB - BetonKalender 201l, and the second punching model alternative is established in Swedish Concrete Association - Report No. 4 1994. Due to missing information of the experimental measured residual tensile strength, a theoretical residual tensile strength was estimated in two different manners to be able to adapt the DAfStB punching model altemative on the refereed test slabs. The first solution is an derivation of a suggestion made by Silfiverbrand (2000) and the second solution is drawn from a proposal made by Choi etal. (2007). The result indicates that the SCA punching model alternative is easier to adapt and provides the most representative result. Also DAfStb altemative with the second solution of estimating the residual strength contributes to arbitrary result, however due to the uncertainty of the estimation of the residual tensile strength, the SCA punching model is recommended to be applied until further investigation can confirm the accuracy of the DAfStB alternative with experimentally obtained residual tensile strength.
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Tetzner, Enzo. "Avaliação das propriedades flexurais de pinos de fibra odontológicos." Universidade Federal do Espírito Santo, 2013. http://repositorio.ufes.br/handle/10/5865.
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Previous issue date: 2013-04-22O objetivo deste estudo é avaliar a resistência flexural (S) e o módulo flexural (E) de três marcas comerciais de pinos de fibra, além de verificar a influência da relação distância entre apoios/diâmetro do pino sobre os valores das propriedades de uma marca comercial por meio de testes de flexão de três pontos. Os grupos estudados foram de pinos de fibra de quartzo (Grupo 1), pinos de fibra de carbono (Grupo 2) e pinos de fibra de vidro (Grupos 3 e 4). Os testes foram realizados em uma máquina de ensaio universal INSTRON 5565® de acordo com as especificações da norma ASTM D2344/D2344M. Após os testes, encontraram-se os seguintes resultados: S de 884,32±45,38C MPa para o Grupo 1; 567,47±36,03A para o Grupo 2, 575,98±44,70A MPa para o grupo 3 e 719,19±75,82 B MPa para o Grupo 4; e E de 15,48±1,72 B GPa para o Grupo 1, 9,44±1,18A GPa para o Grupo 2, 8,83±2,33A GPa para o Grupo 3 e 17,20±2,67B GPa para o Grupo 4. Concluiu-se que os pinos de fibra de quartzo apresentaram propriedades superiores em relação aos pinos de fibra de carbono e de vidro, submetidos à mesma norma nos ensaios. E que o grupo de pinos de fibra de vidro, com a relação distância entre apoios/diâmetro menor, apresentou maior carga máxima e menores resistência flexural e módulo flexural em relação ao grupo de pinos de fibra de vidro com a relação distância entre apoios/diâmetro maior
The present study aims to assess the flexural strengths (S) and flexural moduli (E) of 3 commercial fiber post brands. An additional aim is to test the effect of the distance between supports/post diameter ratio on the properties of a commercial brand with the 3-point bending test. The following groups were studied: quartz fiber posts (Group 1); carbon fiber posts (Group 2); and fiberglass posts (Groups 3 and 4). The tests were conducted on an INSTRON 5565® universal testing machine according to the specifications of the ASTM D2344/D2344M standard. The following results were obtained from the tests: the S values were 884.32±45.38C MPa, 567.47±36.03A, 575.98±44.70A MPa and 719.19±75.82B MPa for Groups 1, 2, 3 and 4, respectively, and the E values were15.48±1.72B GPa, 9.44 GPa±1.18A GPa, 8.83±2.33A GPa and 17.20±2.67B GPa for Groups 1, 2, 3 and4, respectively. We conclude that, under the same test standard, quartz fiber posts have better properties than carbon fiber and fiberglass posts. Additionally, the fiberglass post group with the lower distance between supports/post diameter ratio had a greater maximum load, less flexural strength and a lower flexural modulus than the fiberglass post group with a higher ratio
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Bosi, Federico. "Valutazione sperimentale del comportamento a fatica di materiali compositi sottoposti ad invecchiamento." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15769/.
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Questa tesi si propone di analizzare gli effetti combinati di invecchiamento igroscopico e termico su un set di provini in CFRP (Carbon Fiber Reinforced Polymers), forniti dall’azienda RiBa Composites, sottoponendoli a prove a fatica (taglio interlaminare con carico sinusoidale).
Vista la mancanza di normativa di riferimento per i test a fatica ci si è ispirati a quella in uso per i test statici (ASTM D2344/D2344M). Di conseguenza, la presente tesi ne valuta l’efficacia e l’adeguatezza per la descrizione del comportamento a fatica. Come risultato finale si sono ottenuti i diagrammi di Wöhler per il materiale ai vari livelli di invecchiamento, così da avere uno strumento di previsione per valutazioni future.
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Sencu, Razvan. "Multiscale stochastic fracture mechanics of composites informed by in-situ X-ray CT tests." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/multiscale-stochastic-fracture-mechanics-of-composites-informed-by-insitu-xray-ct-tests(85a0be40-9e7a-4df3-a366-69ac6ce02e35).html.
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This thesis presents the development of a new multiscale stochastic fracture mechanics modelling framework informed by in-situ X-ray Computed Tomography (X-ray CT) tests, which can be used to enhance the quality of new designs and prognosis practices for fibre reinforced composites. To reduce the empiricism and conservatism of existing methods, this PhD research systematically has tackled several challenging tasks including: (i) extension of the cohesive interface crack model to multi-phase composites in both 2D and 3D, (ii) development of a new in-house loading rig to support in-situ X-ray CT tests, (iii) reconstruction of low phase-contrast X-ray CT datasets of carbon fibre composites, (iv) integration of X-ray CT image-based models into detailed crack propagation FE modelling and (v) validation of a partially informed multiscale stochastic modelling method by direct comparison with in-situ X-ray CT tensile test results.
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Michalec, Jiri, and Sylvie Niklasova. "Water uptake of hardwoods." Thesis, Växjö University, School of Technology and Design, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:vxu:diva-960.
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This study investigate water uptake in six different species of hardwood in tangential and radial section. Alder (Alnus glutinosa) and beech (Fagus sylvatika) represent semi-diffuse-porous hardwoods. Aspen (Popolus tremula) and birch (Betula pubescens) represent diffuse-porous group; oak (Quercus robur) and ash (Fraxinus excelsior) the ring-porous hardwoods. Spruce (Picea abies) was used as a reference sample.
Significantly higher water uptake was observed in the diffuse-porous and the semi-diffuse-porous group. Water uptake varied among the species, nevertheless tangential section was more permeable in general. Any impact of density or annual rings width on water uptake was observed. Correlation between ratio of earlywood and latewood and water uptake in dependence on hardwood group was found out. Ring-porous species had low rate of earlywood and low water uptake, whereas diffuse-porous and semi-diffuse-porous hardwoods had high rate of earlywood and high water uptake. Relation between water uptake and microstructure of wood was observed.
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Ciccone, Francesco. "Analisi del taglio interlaminare in materiali compositi." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
Find full textAbstract:
Nel settore aeronautico il materiale più largamente utilizzato è stato l’alluminio; la ricerca scientifica ha prodotto molti test riguardo a questo particolare metallo e le sue proprietà risultano largamente note.
Dagli anni 70 però è entrata in scena la fibra di carbonio, risultando un materiale di utilizzo molto vantaggioso sia per la sua leggerezza, fondamentale per il peso finale degli aerei, sia per le sue proprietà meccaniche, che gli consentono di avere enormi resistenze ai carichi applicati.
Ovviamente gli studi condotti sull’alluminio sono stati fatti riguardo la trazione. All’inizio anche i compositi sono stati studiati a trazione, producendo però un'enorme quantità di dati che purtroppo si sono verificati poco interessanti, al contrario invece degli studi condotti sulla compressione. Questo perché, come si è capito in seguito, i materiali compositi lavorano in maniera differente dall’alluminio e dagli altri metalli.
L’obbiettivo del seguente lavoro è proprio quello di studiare il taglio interlaminare prodotto dalla compressione su materiale in fibra di carbonio. Più nel dettaglio, questa tesi segue un precedente studio condotto dalla dottoressa Monica Damiani, dove i provini in fibra di carbonio sono stati testati analizzando il loro comportamento a fatica. I risultati hanno quindi prodotto la curva S-N o anche detta di Woehler. Analizzando tale curva però, si è riscontrato un dubbio riguardo la precoce rottura di alcuni provini testati applicando il 70% del carico massimo. Tale rottura è avvenuta anche prima di quella dei provini testati all’80% del carico massimo.
Quindi lo studio seguente è stato quello di riproporre il test a fatica su altri provini dello stesso materiale, applicando anche questa volta il 70% del carico. Successivamente si sono analizzati i dati ricavati, facendo un confronto con quelli precedenti, cercando di dare possibili soluzioni al problema.
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Lapena, Mauro Henrique. "Estudo do comportamento mecânico de cilindros de compósito epóxi/fibra de basalto em ensaios hidrostáticos." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-23032017-152933/.
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O objetivo deste trabalho foi estudar o comportamento mecânico de cilindros de compósito polimérico reforçado com fibras. Para isso, foram produzidos cilindros com extremidades abertas reforçados com fibra de basalto e fibra de vidro, utilizando a técnica de enrolamento filamentar (filament winding). Estes cilindros foram submetidos a ensaio hidrostático com carregamento circunferencial, ensaio de ruptura de anel (split disk test) e ensaio de resistência ao cisalhamento interlaminar (ILSS). Uma placa do compósito de fibra de basalto foi produzida por enrolamento filamentar, para caracterização por ensaio de resistência à tração. Todos cilindros submetidos ao ensaio hidrostático apresentaram fratura localizada em uma faixa de altura do cilindro, com extensas delaminações das camadas circunferenciais. Os compósitos epóxi/fibra de basalto superaram ou igualaram os de compósito epóxi/fibra de vidro nas comparações entre resultados dos valores das propriedades mecânicas avaliadas, nas porcentagens: resistência à tração aparente de ruptura de anel em 45% e 43% em resistência específica; ILSS, em 11%; resistência/tensão de membrana de ruptura no ensaio hidrostático, em 55%.The aim of this work was to study the mechanical behavior of fiber reinforced polymer composite cylinders. For this purpose, cylinders reinforced with basalt and glass fibers were produced, with open-ended geometry, using filament winding technique. These cylinders were submitted to hydrostatic test under circunferential loading, split disk (ring segment) test and interlaminar shear strength (ILSS). A basalt fiber composite plate was produced by filament winding for characterization by tensile strength test. All cylinders submitted to hydrostatic test presented fracture located in the height range of the cylinder, with extensive delamination of the circumferential layers. The epoxy/basalt fiber composites overcame or equated the epoxy/glass fiber composites in comparisons between results of the mechanical properties, tensile strength in split disk, in 45% and 43% in specific strength; ILSS in 11%; membrane tensile strength in the hydrostatic test, in 55%.
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Borges, Leonardo Augusto Cruz. "Ensaio de compressão de corpo de prova com duplo corte em cunha na avaliação de concretos com baixos teores de fibra de aço." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3146/tde-11042017-143957/.
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A melhor maneira de se caracterizar o comportamento mecânico pós-fissuração dos concretos reforçados com fibras (CRF) para fins estruturais é por meio de ensaios que envolvem a ruptura do material à tração direta. Devido às dificuldades de execução destes, comumente se empregam ensaios de tração indireta, com destaque para os ensaios de flexão com sistema fechado. Entretanto, fatores limitantes, como a superestimação da capacidade resistente do compósito em testes de flexão, têm incentivado o desenvolvimento de outros métodos de ensaio mais fidedignos às características do CRF. Este é o caso do ensaio de compressão de corpo de prova com duplo corte em cunha, abreviado como DEWS (do inglês, Double Edge Wedge Splitting), em que o esforço de tração indireta não está associado a uma flecha, como nos ensaios de flexão, mas sim à própria fissuração da matriz de concreto. No DEWS há a possibilidade de avaliação direta da ortotropia do CRF e seu efeito na resistência pós-fissuração no estado limite de serviço (ELS) e último (ELU). Estudos anteriores sobre este ensaio utilizaram sistema aberto, mas se restringiram a avaliar apenas elevados teores de fibra, o que não traz dificuldades à caracterização da resistência residual no ELS. Este trabalho, contudo, buscou o estudo mais acurado a respeito do ensaio DEWS. Os programas experimentais desenvolvidos empregaram concretos reforçados com baixos teores de fibra de aço. Inicialmente, estudou-se a capacidade do ensaio DEWS em identificar o efeito da orientação das fibras na matriz na resistência pós-fissuração do CRF. Essa análise foi correlacionada com os resultados obtidos a partir de ensaios de flexão de prismas feitos como recomendado pela JSCE-SF4, assim, buscou-se avaliar se este teste promove uma superestimação da capacidade de reforço da fibra. Uma outra avaliação centrou-se no fator da taxa de carregamento de ensaio, realizando-se a metodologia DEWS e o teste de flexão (JSCE-SF4: 1984) sob quatro velocidades distintas, com intuito de verificar seu grau de influência no comportamento do material. A partir dos resultados obtidos, o ensaio DEWS mostrou-se aplicável na avaliação da ortotropia de corpos de prova em concretos reforçados com baixos teores de fibra de aço, mesmo com a utilização de sistema aberto e em velocidade de carregamento acima da proposta em literatura. A extensão da instabilidade pós-fissuração obtida a partir do ensaio DEWS foi menor que a encontrada para o ensaio de flexão de prismas. O estudo mostrou que a capacidade resistente pós-fissuração do CRF no ensaio de flexão pode ser até 300% maior do que a mesma resistência medida na direção transversal do prisma.The best way to characterize the post-cracking behaviour of fibre reinforced concretes (FRC) for structural proposes is through direct tensile tests. As direct tensile tests are difficult to conduce, usually indirect tensile tests are employed, especially bending tests with closed-loop control. However, limiting factors, as the strength capacity overestimation of composites under flexural beams tests had motivated the development of another test procedure aiming to obtain responses closer to FRC basic characteristics. This is the case of Double Edge Wedge Splitting test (DEWS). In this test, the indirect tensile stress is not associated with a deflection - as is common in bending tests - but it is related with the cracking opening of concrete matrix. The DEWS test brings the possibility of direct evaluation of the FRC orthotropic behaviour and its effect in the post-crack strength at the serviceability (SLS) and ultimate (ULS) limit estates. Previous researches about DEWS test were done using open-loop control, but they were limited to higher fibre content. These do not provide difficulties about the residual strength characterization at the SLS. Thus, this study carried out an accurate experimental analysis about DEWS. This experimental programme used only fibre reinforced concrete with low steel fibre volume fractions. The first analysis was based in the DEWS test capacity for identification of the effect of predominant fibre orientation into matrix in the post-crack strength of the FRC. This analysis was linked with the flexural test made with prismatic specimens as recommended by JSCE-SF4 in order to evaluate if it promotes an overestimation of the fibre reinforcement capacity. The other evaluation focused on the test loading rate factor by doing DEWS test and bending test (JSCE-SF4:1984) under four different rates in order to verify its influence on the material behaviour. The results shown that DEWS test was capable to identify the fibre alignment into FRC specimens with low fibre content, even using open-loop control and increasing the load rate. The extension of the instability region on DEWS test response was lower than the provided by the flexural tests. The study also showed that the flexural test could overestimate the post-crack strength capacity of the FRC up 300% in relation to the transversal direction.
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Oliveira, Roberto Caetano. "Teste de vigor em sementes de azevém em diferentes substratos e profundidades de semeadura." Universidade Federal de Pelotas, 2016. http://guaiaca.ufpel.edu.br:8080/handle/prefix/4016.
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A qualidade fisiológica inadequada de sementes de azevém tem resultado em pastagens com inadequado estande de plantas para a cobertura do solo e, sobretudo, para a exploração forrageira. Neste sentido, o presente trabalho tem como principal objetivo propor um teste de vigor para sementes de azevém de fácil aplicação e de baixo custo. Para isto foi proposto testar diferentes profundidades de semeadura (0,5; 1,0; 1,5; 2,0; 2,5 e 3cm) em três diferentes substratos (areia, fibra de côco e casca de arroz carbonizada) para diferenciar a qualidade fisiológica de 4 lotes que apresentaram semelhança quanto ao teste de germinação e umidade, porém diferenças quanto ao vigor a partir das análises de emergência em campo, peso de mil sementes, envelhecimento acelerado, primeira contagem da germinação e condutividade elétrica. Estes testes serviram para ranquear os lotes de acordo com o vigor. O trabalho foi conduzido no Laboratório Didático de Análise de Sementes LDAS na Faculdade de Agronomia “Eliseu Maciel” (FAEM), Universidade Federal de Pelotas. O delineamento experimental foi o de blocos inteiramente casualizados. Os dados foram submetidos à análise de variância através do teste F e as médias, comparadas entre si pelo teste de Scott-Knot, a 5% de probabilidade. Os resultados demonstraram que a profundidade de semeadura foi um teste eficiente para determinar o vigor de sementes de azevém anual, especialmente quando os substratos foram de areia e de fibra de côco. As variáveis que melhor expressaram o vigor da semente de azevém anual semeado em diferentes profundidades foram a emergência de plântulas e o índice de velocidade de emergência. A partir da porcentagem de emergência de plântulas semeadas em areia a 2,5 cm e em fibra de côco a 2,5 e 3cm de profundidade, foi possível determinar o vigor de sementes de azevém anual. Porém, quando a variável resposta foi o índice de velocidade de emergência de plântulas, a profundidade de semeadura mais interessante para determinar o vigor das sementes foi de 2,5cm, quando o substrato foi areia e, de 3cm, quando o substrato foi fibra de coco.
The inadequate physiological quality of ryegrass seeds has resulted in pastures with inadequate plant stands for soil cover and, especially, forage exploitation. In this sense, the main objective of this work is to propose a vigor test for ryegrass seeds of easy application and low cost. For this purpose, it was proposed to test different sowing depths (0.5, 1.0, 1.5, 2.0, 2.5 and 3 cm) on three different substrates (sand, coconut fiber and charcoal rice husk) to differentiate The physiological quality of 4 lots that presented similarity to the germination and humidity test, but differences as to vigor from the field emergency analysis, thousand seed weight, accelerated aging, first germination count and electrical conductivity. These tests were used to rank the lots according to the vigor. The work will be conducted in the Didactic Laboratory LDAS Seed Analysis at the “Faculdade de Agronomia Eliseu Maciel (FAEM), Universidade Federal de Pelotas”. The experimental design was a completely randomized block design. The data were submitted to analysis of variance through the F test and the means, compared to each other by the Scott-Knot test, at 5% probability. The results demonstrated that sowing depth was an efficient test to determine the vigor of annual ryegrass seeds, especially when the substrates were sand and coconut fiber. The variables that best expressed the vigor of the annual ryegrass seed sown at different depths were the emergence of seedlings and the rate of emergence speed. From the emergence percentage of seedlings sown in 2.5 cm sand and coconut fiber 2.5 and 3 cm depth, it was possible to determine the vigor of annual ryegrass seeds. However, when the response variable was the seedling emergence rate index, the most interesting seeding depth to determine seed vigor was 2.5 cm, when the substrate was sand and 3 cm when the substrate was coconut fiber.
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Silva, Luciana Mendonça da. "Resistência da união da cimentação adesiva de pinos de fibra de vidro frente ao teste de remoção por extrusão." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/25/25131/tde-29052009-100558/.
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Este trabalho avaliou a resistência de união de pinos de fibra de vidro cimentados à dentina com o uso de um cimento resinoso convencional e um auto-adesivo. Trinta dentes bovinos unirradiculares tiveram as raízes 17mm a partir dos ápices. As raizes foram tratadas endodonticamente e divididas aleatoriamente em 3 grupos (n=10): G1- cimento resinoso convencional RelyX ARC + ScotchBond Multi Uso Plus (SBMP) fotoativado + pino de fibra de vidro; G2 RelyX ARC + SBMP quimicamente ativado + pino de fibra de vidro; G3 cimento resinoso auto-adesivo RelyX U100 + pino de fibra de vidro. Após a cimentação dos pinos, os espécimes foram armazenados por 24 horas em água destilada, à 37oC. As raízes foram cortadas sob irrigação constante para obter de 6 a 9 fatias de 1mm de espessura. O teste de resistência à extrusão foi realizado para medir a resistência adesiva nas fatias da região cervical, média e apical, a uma velocidade de 0,5mm/min. Todos os espécimes foram observados em microscópio ótico de luz para avaliar os tipos de falhas. Os valores foram submetidos à análise de variância a dois critérios (ANOVA) e teste de Tukey (p0,05). As médias gerais dos grupos 1, 2 e 3, respectivamente, (MPa) foram de 4,87 (±3,65); 5,89(±3,72); e 8,50(±4,52). Os valores de resistência adesiva regional nos terços cervical, médio e radicular, respectivamente, foram: G1- 5,26(±3,44); 5,11(±3,33); 5,01(±3,17); G2- 7,45(±3,82); 5,88(±2,50); 4,91(±2,74); G3- 10,11(±3,11); 9,12(±3,70); 4,99(±3,28). Os maiores valores de resistência adesiva foram encontrados com o cimento auto-adesivo. Ao avaliar os terços separadamente, os grupos 2 e 3 obtiveram comportamento semelhante nos terços cervical e médio. No terço apical, todos os grupos tiveram o mesmo comportamento. A resistência de união foi influenciada pelo tipo de cimento utilizado e região radicular, mas não foi alterada pela variação do modo de polimerização do sistema adesivo.This work evaluated the bond strength of glass fiber posts to dentin using a conventional and a self-adhesive resin cement. Thirty bovine incisors had their roots sectioned 17mm from their apices, endodontically treated and assigned into 3 groups (n=10): group 1, conventional resin cement RelyX ARC + ScotchBond Multi Purpose Plus (SBMP) light activated + glass fiber post; Group 2, RelyX ARC+ SBMP chemically activated + glass fiber post; Group 3, self-adhesive resin cement RelyX U100 + glass fiber post. After luting, specimens were stored for 24 hours in distilled water at 37oC. Roots were sliced under water irrigation to obtain 1mm thick slices. Push-out test was performed on each slice with a universal testing machine with a crosshead speed of 0,5mm/min. All fractured specimens were observed using a light microscope to identify modes of failure. Values were submitted to two-way ANOVA and Tukeys test (p0,05). Mean values (MPa) and standard deviation for groups 1, 2 and 3 were, respectively: 4.87 (±3.65); 5.89(±3.72); e 8.50(±4.52). Regional bond strength values for the cervical, medium and apical were: G1- 5.26(±3.44); 5.11(±3.33); 5.01(±3.17); G2- 7.45(±3.82); 5.88(±2.50); 4.91(±2.74); G3- 10.11(±3.11); 9.12(±3.70); 4.99(±3.28). The highest bond strength values were obtained using the self-adhesive cement. Regional bond strengths were similar in the cervical and medium region in groups 2 and 3. All cements had the same performance on the apical region. Bond strength was influenced by the type of cement used and radicular region, but was not altered by the activation mode of the bonding system.
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López, Martínez Juan Ángel. "CHARACTERISATION OF THE TENSILE BEHAVIOUR OF UHPFRC BY MEANS OF FOUR-POINT BENDING TESTS." Doctoral thesis, Universitat Politècnica de València, 2017. http://hdl.handle.net/10251/79740.
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Combining the most recent technologies in concrete, Ultra-High-Performance Fibre-Reinforced Concrete (UHPFRC) arises as a promising material for the near future. UHPFRC have shown how flexible concrete can be to adapt to the ever-changing social and environmental demands. With its high flexibility composition and its mechanical properties, UHPFRC is full of both unexplored and unexploited possibilities. Engineers should take responsibility for this task. However, it is fair to acknowledge that this is not an easy task and it requires the development of reliable and widely accepted design standards provided by the scientific community.
A major concern about durability, long-lasting structures and reduction of maintenance cost, as well as the development of new concrete technologies, improved knowledge of fibre effect and a huge growth in the fibre industry accompanied by fibre price reduction have led, among other factors, to the development of new types of concrete whose mechanical behaviour substantially differs from conventional fibre-reinforced concrete. This is why current characterisation methodologies and design standards must be reviewed and adjusted to these newer materials. However, design standard revision cannot disregard former milestones achieved thanks to decades of hard work. It must offer an integrated view in which new types of concrete comprise existing ones in a broader group, because at the end of the day and despite having newer and improved properties, new types of concrete are still concrete. That is how it should be understood and how it must be reflected in newer codes and standards.
The work presented herein is focused on one of these recently developed materials that embraces major advanced technologies in concrete: Ultra-High-Performance Fibre-Reinforced Concrete (UHPFRC). This work is specifically focused on those crucial requirements for the development and widespread use of it, such as constitutive tensile characterisation and classification. This work includes a deep revision of the uniaxial tensile behaviour of concrete and its development as fibre technology has evolved. In addition, traditional characterisation standard methods as well as those recently developed for its specific use on UHPFRC are reviewed and called into question.
Throughout the document, the development of different methodologies to determine the uniaxial constitutive tensile behaviour of UHPFRC from bending tests are shown, together with a simplified characterisation proposal specially developed for being included in a standard. All developed methodologies presented herein are checked and validated. These methods are specifically designed for their application on experimental results obtained from a special type of four-point bending test, whose standardisation proposal for UHPFRC is also shown.
Finally, a classification proposal is presented as a function of more relevant UHPFRC tensile parameters necessary for design that can be directly obtained from the standard characterisation test method suggested. Proposed classification encompasses the existing classification for conventional reinforced and fibre-reinforced concrete. In it, both plain concrete and fibre-reinforced concrete are presented as a particular case of a more general tensile constitutive response for concrete. Standard methodology and classification proposed are in accordance with the evolution of concrete and unify historic milestones achieved by the international research community.El Hormigón de Muy Alto Rendimiento (HMAR) combina los últimos avances tecnológicos en hormigón y se erige como un material prometedor para el futuro. El HMAR ha demostrado su gran capacidad para adaptarse a las cada vez más exigentes demandas sociales y medioambientales. Con un gran abanico de posibilidades en su dosificación para conseguir las propiedades mecánicas deseadas, el HMAR es un material lleno de posibilidades aún sin explorar y sin explotar. Los ingenieros tienen la responsabilidad de esta tarea. Sin embargo, es justo reconocer que no se trata de una tarea fácil y que requiere de un desarrollo previo de códigos de diseño adecuados y ampliamente aceptados por parte de la comunidad científica. La aparición de nuevas tecnologías, el mayor conocimiento sobre la aportación de las fibras así como su industrialización y bajada de precios, las mayores preocupaciones sobre la durabilidad estructural, incremento de la vida útil o la reducción de los costes de mantenimiento, entre otros factores, han derivado en el desarrollo de nuevas tipologías de hormigones cuyo comportamiento mecánico difiere de manera sustancial de los tradicionales hormigones con fibras. Es por ello que tanto la readaptación de las metodologías de caracterización como las metodologías de diseño deben ser reformuladas. Y esto debe hacerse de manera no disruptiva, es decir, manteniendo la línea de los hitos alcanzados en los hormigones con fibras convencionales de manera que queden integrados en metodologías de caracterización y de diseño que los engloben, porque al fin y al cabo, y aunque con nuevas y mejores propiedades mecánicas, los nuevos hormigones siguen siendo hormigones. Así debe ser entendido y así debe quedar reflejado en las nuevas normativas. El presente trabajo se centra en uno de esos nuevos materiales desarrollados con el avance de las nuevas tecnologías como es el HMAR. En especial, este documento se centra en ese aspecto tan fundamental para el desarrollo de nuevos hormigones como es la caracterización mecánica y la tipificación. Este trabajo incluye una revisión del comportamiento mecánico uniaxial a tracción del hormigón y de su evolución con la aparición de las diferentes tecnologías. Además, se revisan y se ponen en cuestión los sistemas tradicionales de caracterización, así como los nuevos sistemas desarrollados en los últimos años para su empleo específico en el HMAR. A lo largo del documento se desarrollan diferentes metodologías para la obtención del comportamiento constitutivo a tracción del HMAR, así como la propuesta de una metdología simplificada de caracterización especialmente diseñada para ser incluida en una norma, todas ellas debidamente validadas. Estas metodologías son de aplicación específica a los resultados experimentales obtenidos mediante un ensayo a cuatro puntos sin entalla, cuya propuesta de estandarización para el HMAR ha sido también desarrollada. Finalmente, se presenta una propuesta de tipificación de acuerdo a los parámetros más relevantes del comportamiento a tracción del HMAR que son necesarios para el diseño y que pueden ser directamente obtenidos del ensayo de caracterización propuesto. Esta clasificación engloba a la clasificación existente para el hormigón armado convencional y los actuales hormigones con fibras, de manera que se presenta la actual definición de hormigón con fibras como un caso particular de estos nuevos hormigones, respetando al máximo la evolución de este material y aunando los logros conseguidos por la comunidad científica.
Dins de les combinacions de les tecnologies més recents en el formigó, el formigó de molt alt rendiment (UHPFRC) sorgeix com un material prometedor per al futur pròxim. L'UHPFRC ha demostrat poder ser un formigó flexible per adaptar-se a les sempre canviants demandes socials i mediambientals. Amb una gran flexibilitat en la seua composició i les seues propietats mecàniques, l`UHPFRC està ple de possibilitats de ser explorades i explotades. Els enginyers han de prendre la responsabilitat d'aquesta tasca. No obstant això, és just reconèixer que això no serà fàcil i requerirà el desenvolupament de normes de disseny fiables i àmpliament acceptades per la comunitat científica. Hi ha una gran preocupació al voltant de la durabilitat, la vida útil de les estructures i la reducció del cost de manteniment, juntament amb el desenvolupament de noves tecnologies de formigó, un millor coneixement de l'efecte de la fibra i un enorme creixement en la indústria de la fibra acompanyat per la reducció del preu de la fibra, han conduït, entre altres factors, al desenvolupament de nous tipus de formigons, el comportament mecànic dels quals es diferencia substancialment dels formigons reforçats amb fibres convencionals. És per això que les metodologies de caracterització actuals i les normes de disseny han de ser revisades i ajustades a aquests nous materials. No obstant això, la revisió del codis de disseny no pot prescindir de les antigues fites aconseguides gràcies a dècades de treball dur. S'ha d'oferir una visió integrada en la qual els nous tipus de formigons integren els ja existents en un grup més ampli, ja que, al cap i la fi i malgrat tenir propietats noves i millorades, els nous tipus de formigons són encara un tipus de formigó. Així es com s'hauria d'entendre i reflectir-se en els nous codis i normes. El treball presentat en aquest document es centra en un d'aquests materials que s'han desenvolupat recentment i que abasta les principals tecnologies avançades en el formigó: el Formigó de Molt Alt Rendiment Reforçat amb Fibres (UHPFRC). Aquest treball se centra específicament en els requisits fonamentals per al desenvolupament i l'ús generalitzat d'aquest, com ara la caracterització i classificació del comportament constitutiu a tracció. Aquest treball inclou una revisió profunda del comportament a tracció uniaxial del formigó i els seus canvis al temps que la tecnologia de les fibres ha evolucionat. A més, els mètodes tradicionals estàndard de caracterització, així com els recentment desenvolupats per al seu ús específic en l'UHPFRC són revisats i qüestionats. Al llarg del document, es mostra el desenvolupament de diferents metodologies per a determinar el comportament constitutiu a tracció uniaxial de l'UHPFRC, juntament amb una proposta de caracterització simplificada especialment desenvolupada per poder ser inclosa en normativa. Totes les metodologies desenvolupades presentades en aquest document han estat comprovades i validades. Aquests mètodes estan dissenyats específicament per a la seva aplicació en els resultats experimentals obtinguts a partir d'un tipus especial d'assaig de flexió a quatre punts, a més també s'inclou una proposta d'estandardització per a l'UHPFRC. Finalment, es presenta una proposta de classificació en funció dels paràmetres més rellevants del comportament a tracció de l'UHPFRC que són necessaris per al disseny i que es poden obtindre directament del mètode d'assaig estàndard suggerit per a la caracterització de l'UHPFRC. La classificació proposada té amb compte la classificació existent per al formigó armat convencional i el reforçat amb fibres. En ella, tant el formigó en massa com el formigó reforçat amb fibres es presenten com un cas particular d'una resposta constitutiva a tracció més general per al formigó. La metodologia estàndard i la classificació proposada estan d'acord amb l'evolució de formigó i unifica l
López Martínez, JÁ. (2017). CHARACTERISATION OF THE TENSILE BEHAVIOUR OF UHPFRC BY MEANS OF FOUR-POINT BENDING TESTS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/79740
TESIS
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Berg, Jan-Erik. "Wood and fibre mechanics related to the thermomechanical pulping process." Doctoral thesis, Mittuniversitetet, Institutionen för naturvetenskap, teknik och matematik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-6725.
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The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner. The thesis comprises the following parts: –A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process –An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners –An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner –A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone –Measurements of the power distribution in a refiner. The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given. The fibre separation step and specifically the effect of impact velocity on the fracture energy were studied by use of a falling weight impact tester. The fracture surfaces were also examined under a microscope. An increase in impact velocity resulted in an increase in fracture energy. In the thermomechanical pulping process the fibres are subjected to lateral compression, tension and shear which causes the creation of microcracks in the fibre wall. This damage reduces the fibre wall stiffness. A simplified analytical model is presented for the prediction of the stiffness degradation due to the damage state in a wood fibre, loaded in uni-axial tension or shear. The model was based on an assumed displacement field together with the minimum total potential energy theorem. For the damage development an energy criterion was employed. The model was applied to calculate the relevant stiffness coefficients as a function of the damage state. The energy consumption in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load was also calculated. The energy consumption was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy was needed to create cracks at higher microfibril angles. The energy consumption was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy consumption was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data. Only a part of the electrical energy demand in the thermomechanical pulping process is considered to be effective in fibre separation and developing fibre properties. Therefore it is important to improve the understanding of how this energy is distributed along the refining zone. Investigations have been carried out in a laboratory single-disc refiner. It was found that a new developed force sensor is an effective way of measuring the power distribution within the refining zone. The collected data show that the tangential force per area and consequently also the power per unit area increased with radial position. The results in this thesis improve the understanding of the influence of some process parameters in thermomechanical pulping related wood and fibre mechanics such as loading rate, loading direction, moisture content and temperature to separate the fibres from the wood and to achieve desired irreversible changes in the fibre structure. Further, the thesis gives an insight of the spatial energy distribution in a refiner during thermomechanical pulping.
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Gonçalves, Mariella Agostinho. "Resistência da união ao teste de push-out de cimentos resinosos auto-adesivos em dentina radicular." Universidade Federal de Juiz de Fora, 2012. https://repositorio.ufjf.br/jspui/handle/ufjf/1580.
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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Neste estudo, avaliou-se a resistência da união ao push-out de dois cimentos resinosos auto-adesivos e de um cimento resinoso convencional em dentina radicular. Em 60 dentes terceiros molares humanos, tratados endodonticamente, um pino de fibra de vidro foi cimentado com um dos três cimentos resinosos. Cada raiz foi seccionada em sentido transversal para a obtenção de três fatias (dentina-pino) de 1 mm de espessura. As fatias, correspondentes aos terços cervical, médio e apical do canal radicular, foram armazenadas em água deionizada a 37 ºC, durante 24 horas ou 30 dias. Após o teste de push-out, os valores de resistência da união foram submetidos aos testes estatísticos ANOVA three way e Tuckey (p = 0,05) e os tipos de fratura foram avaliados através de microscopia eletrônica de varredura. A resistência da união do cimento resinoso auto-adesivo RelyX U100 foi superior à do cimento convencional RelyX ARC, após os dois períodos de armazenamento (p < 0,05). No terço cervical, os valores de resistência da união do cimento resinoso convencional RelyX ARC foram maiores que nos terços médio e apical (p < 0,05) na análise de 24 horas. Após 30 dias de armazenamento, os valores nos três terços radiculares não diferiram entre si. Os valores de resistência da união do cimento resinoso RelyX U100, nas três regiões do canal radicular, não diferiram entre si (p > 0,05), em ambos os momentos de avaliação. Após 24 horas, BisCem apresentou maior resistência da união no terço apical, seguido pelo terço cervical. Após 30 dias, os valores de resistência da união nos três terços radiculares não diferiram entre si (p > 0,05). RelyX U100 não sofreu alteração nos valores de resistência da união após 30 dias de envelhecimento (p > 0,05). BisCem não apresentou diferenças nos valores obtidos após 24 horas e 30 dias de envelhecimento nos terços cervical e médio (p > 0,05). Para RelyX ARC, o tempo de 30 dias reduziu os valores de resistência da união nos três terços radiculares. RelyX U100 e BisCem apresentaram maior número de falhas coesivas da zona de interação. Para RelyX ARC, observou-se maior número de falhas coesivas da camada híbrida. Concluiu-se que o cimento resinoso auto-adesivo RelyX U100 apresentou maior resistência da união que o cimento resinoso convencional RelyX ARC, nos três terços radiculares, nos dois momentos de avaliação. BisCem demonstrou resistência da união comparável a do cimento RelyX U100. O tempo de armazenamento por 30 dias provocou alteração na resistência da união dos cimentos resinosos RelyX ARC e BisCem.
This study evaluated the push-out bond strength of two self-adhesive resin cements and a conventional etch-and-rinse resin cement on root dentin. Sixty human third molars were endodontically treated and a glass fiber post was cemented with one of three resin cements. Each root was cut transversely to obtain three slices (dentin-post) of 1 mm thick. The slices of the cervical, middle and apical root canal were stored in deionized water at 37 °C for 24 hours or 30 days. After storage, the push-out test was performed. The values of bond strength were evaluated by ANOVA three way and Tuckey’ test (p = 0,05) and the types of fracture were evaluated by scanning electron microscopy. The bond strength of the self-adhesive resin cement RelyX U100 was superior to the RelyX ARC etch-and-rinse cement, after the two storage periods (p > 0.05). The analysis of 24 hours showed that at the cervical third, the values of bond strength of RelyX ARC were higher than that of the middle and apical thirds (p < 0.05). After 30 days of storage, the values at the three root thirds did not differ. The values of RelyX U100, on the three regions of the root canal did not differ, in both evaluations (p > 0.05). After 24 hours, BisCem showed higher bond strength at the apical third, followed by cervical. After 30 days, the values of bond strength at the three root thirds did not differ (p > 0.05). RelyX U100 did not exhibit changes in bond strength values after 30 days of storage (p > 0.05). BisCem showed no differences in the values obtained after 24 hours and 30 days of aging at the cervical and middle thirds (p > 0.05). The storage time of 30 days reduced the values of bond strength at the three root thirds of RelyX ARC. RelyX U100 e BisCem had the highest number of cohesive failures of the zone of interaction. RelyX ARC presented a higher number of cohesive failures of the hybrid layer were observed. It was concluded that the RelyX U100 self-adhesive resin cement showed higher bond strength than the conventional resin cement RelyX ARC, on the three root thirds, in both periods. BisCem showed bond strength comparable to RelyX U100. The storage time for 30 days caused changes on the bond strength of the RelyX ARC and BisCem resin cements.
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LAPENA, MAURO H. "Estudo do comportamento mecânico de cilindros de compósito epóxi/fibra de basalto em ensaios hidrostáticos." reponame:Repositório Institucional do IPEN, 2017. http://repositorio.ipen.br:8080/xmlui/handle/123456789/28046.
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O objetivo deste trabalho foi estudar o comportamento mecânico de cilindros de compósito polimérico reforçado com fibras. Para isso, foram produzidos cilindros com extremidades abertas reforçados com fibra de basalto e fibra de vidro, utilizando a técnica de enrolamento filamentar (filament winding). Estes cilindros foram submetidos a ensaio hidrostático com carregamento circunferencial, ensaio de ruptura de anel (split disk test) e ensaio de resistência ao cisalhamento interlaminar (ILSS). Uma placa do compósito de fibra de basalto foi produzida por enrolamento filamentar, para caracterização por ensaio de resistência à tração. Todos cilindros submetidos ao ensaio hidrostático apresentaram fratura localizada em uma faixa de altura do cilindro, com extensas delaminações das camadas circunferenciais. Os compósitos epóxi/fibra de basalto superaram ou igualaram os de compósito epóxi/fibra de vidro nas comparações entre resultados dos valores das propriedades mecânicas avaliadas, nas porcentagens: resistência à tração aparente de ruptura de anel em 45% e 43% em resistência específica; ILSS, em 11%; resistência/tensão de membrana de ruptura no ensaio hidrostático, em 55%.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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Sans, Canovas Daniel. "Advances in fibre Bragg grating sensors for damage detection in composite laminates: application in quasi-static and fatigue delamination tests." Doctoral thesis, Universitat de Girona, 2013. http://hdl.handle.net/10803/117357.
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The use of composite materials in industrial applications such as aeronautical, aerospace or wind energy production has greatly increased in recent decades. Due to their inherent properties, these materials allow lighter, larger and more resistant structures. However, the use of composite materials for components or structures with highly stringent requirements, is hampered by the lack of knowledge of their reliability. In this thesis, some fundamental aspects about the use of fibre Bragg grating (FBG) sensors for internal strain measurements in composite laminates are discussed. In addition, a highly accurate method for locating the crack tip position in mixed-mode delamination growth has been presented. Finally, an experimental application of FBGs to dynamic measurements in mode I fatigue test has been performedL’ús de materials compostos en aplicacions de caràcter industrial com per exemple l’aeronàutica, aeroespacial o la de producció d’energia eòlica, ha crescut exponencialment durant les últimes dècades. Degut a les seves extraordinàries propietats, l’ús d’aquests materials permet la construcció d’estructures més lleugeres, grans i resistents, tot i que el seu ús en components d’alta responsabilitat estructural està limitat per la manca de coneixement en relació a la seva fiabilitat estructural. En aquesta tesi es discuteixen alguns aspectes significants sobre l’ús de FBGs per a mesurar camps de deformació en l’interior de laminats de material compòsit, s’ha analitzat també la capacitat de localització de la punta d’una esquerda en creixement de mode mixt i per últim s’ha desenvolupat una aplicació pràctica dels FBG en temps real en assaigs a fatiga en mode I
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Moreillon, Lionel. "Shear strength of structural elements in high performance fibre reinforced concrete (HPFRC)." Phd thesis, Université Paris-Est, 2013. http://pastel.archives-ouvertes.fr/pastel-00861175.
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For members and flat slabs without shear reinforcement, the shear and punching shear strength are often the determining design criteria. These failure modes are characterized by a fragile behaviour implying possible partial or total collapse of the structure. Despite extensive research in this field, shear and punching shear in reinforced and prestressed concrete structures, remain complex phenomena so much that the current approach is often empirical or simplified. The ability of Steel Fibre Reinforced Concrete (SFRC) to reduce shear reinforcement in reinforced and prestressed concrete members and slabs,or even eliminate it, is supported by several experimental studies. However its practical application remains marginal mainly due to the lack of standard, procedures and rules adapted to its performance. The stationary processes in precast industry offer optimal possibilities for using high performance cementitious materials such as Self Compacting Concrete (SCC) and High Strength Concrete (HSC). For the author, the combination of High Performance Concrete and steel fibres is the following step in the development and the optimization of this industry. The High Performance Fibre Reinforced Concrete (HPFRC) stands between conventional SFRC and Ultra-High Performance Fibre Reinforced Concrete (UHPFRC). The HPFRC exhibiting a good strength/cost ratio is, thus, an alternative of UHPFRC for precast elements. The principal aim of this work was to analyse the shear and punching shear behaviour of HPFRC and UHPFRC structures without transversal reinforcement and to propose recommendations and design models adapted for practitioners. Several experimental studies on structural elements, i.e. beams and slabs, were undertaken for this purpose. Firstly, an original experimental campaign was performed on pre-tensioned members in HPFRC. A total number of six shear-critical beams of a 3.6 m span each, and two full scale beams of a 12 m span each, were tested in order to evaluate the shear and flexural strength. The principal parameter between the specimens was the fibres (...)