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Valero, Diana (Diana E. ). "Compression testing and measurement of material properties of a double network hydrogel." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98758.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (page 26).
Double network hydrogel samples were synthesized and manufactured out of polyacrylamide (PAAm) and alginate solutions. They were casted into cube molds with each side measuring 20 mm. Samples were tested under compressive loads in cyclic compression tests and stress relaxation tests. A viscoelastic model was applied and material properties were calculated using the experimental data. The elastic modulus of these PAAm-alginate gels was found to be 35kPa, while the viscosity, [eta], was found to be 1.43 kPa-s. The viscous response was found to have a dependency on the strain rate by an exponential factor of 0.26. Using the applied theoretical model and the experimentally determined material properties, you can then characterize the mechanical response of the PAAm-alginate hydrogel when it undergoes small strains.
by Diana Valero.
S.B.
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Roselli, Eric (Eric J. ). "Design of a testing device for quasi-confined compression of lithium-ion battery cells." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68922.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 29).
The Impact and Crashworthiness Laboratory at MIT has formed a battery consortium to promote research concerning the crash characteristics of new lithium-ion battery technologies as used in automotive applications. Within a broad range of tests, there was a need to perform compression tests with a variable amount of confinement. A spring-loaded detainment device was designed which allows the battery to be confined in the axis perpendicular to compression without completely rigid walls. This provides a testing environment far more similar to the conditions of a real world crash situation. During an automobile crash event, the battery pack acts as a unit where each individual cell may experience a range of stresses from nearby cells or pack walls. An appropriate device was designed in Solidworks and used in the MIT ICL for testing with adjustable confinement during compression testing. MIT's research as a part of the consortium will continue for 3 more years beyond these initial tests. Never the less, the coming computational and constitutive models will be built using initial individual cell testing. Any model of a complete battery pack will use the material properties derived from cell testing.
by Eric Roselli.
S.B.
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Vannutelli, Rafaela S. "Mechanical Behavior of 3D Printed Lattice-Structured Materials." Youngstown State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1516313745997898.
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Toledo, García Gustavo A. "High temperature compression testing of hardened steels for plasticity behavior modeling." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/16909.
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Gardner, Kevin Alexander. "Experimental Techniques for Shear Testing of Thin Sheet Metals and Compression Testing at Intermediate Strain Rates." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366199322.
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King, Carin Palmer. "Methods development of multimodal loading under bending, compression and torsion for bench-top testing of cardiovascular stents." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83723.
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Thesis (S.B.)--Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (page 30).
This thesis describes a method for setting up, testing and analyzing cardiovascular stents in multiple deformation modes. Testing stents in multiple deformation modes, including bending, torsion and compression simultaneously is a novel technique. Specific details are provided on strategies for inserting a stent sample into the testing apparatus such that stent integrity is preserved. Using a dynamic feedback cycle for buffered video capture we have been able to document sequential fracture events during testing scenarios. Stereomicroscopy further allows us to detect and determine placement of stent fracture. This method will help stent designers to create stents that are more likely to stand up to the particular conditions they will face in the body and regulatory agencies to determine how well potential new stents will fair under physiologic conditions.
by Carin Palmer King.
S.B.
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Forrester, Hsuan-Hsiou. "High strain rate compression testing of polymers : PTFE, PCTFE, PVC and PMMA." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13624.
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The mechanically compressive flow stress sensitivities of various polymers are investigated at high strain rates above 103 s-1. Temperatures near the glass transition temperature are investigated and the polymer stress-strain responses have been studied from ambient temperature to 100°C. Previous work has reported peaks in flow stress as a function of strain rate [Al-Maliky/Parry 1994, Al-Maliky 1997]. The analyses showed rapid increases of flow stress followed by a sudden drop at elevated strain rates, which is unlike the well known linear relationship documented at the low strain rates. The mechanics and stipulation of what bring about this phenomenon, or the types of polymers influenced are still unclear. Two fluoropolymers, polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE), and two vinyl polymers, polyvinylchloride (PVC) and polymethylmethacrylate (PMMA), are chosen for this study. PTFE, PCTFE and PVC are semi-crystalline polymers with different percentage of crystallinity contents, whereas PMMA is an amorphous polymer. The glass transition temperature, Tg, is the characteristic of the amorphous content in polymers, which has been suggested to influence the flow stress peaks [Swallowe/Lee 2003]. Tg of the semi-crystalline polymers are within the test temperature range. High strain rate compression tests have been carried out using the split Hopkinson pressure bar (SHPB). This is a well-established method for determining the stress, strain, and strain rate of materials. The strain rate range of interest is 103 s-1 to 105 s-1 where the strain rate sensitivity has previously been identified [Al-Maliky/Parry 1994, Al-Maliky 1997, Walley/Field 1994]. Two thermal analyses techniques are used to quantify the dependency of the viscoelastic behaviour in relation to time and temperature. Differential scanning calorimetry (DSC) measures the enthalpy of the polymers to show how the materials are affected by heat, and Dynamic mechanical analysis (DMA) is used to characterise the time-temperature dependence of the elastic storage and loss moduli of the polymers A total of 42 PCTFE, 44 PTFE, 45 PVC and 55 PMMA specimens were tested using the SHPB system, with the strain rate varying between 1600 s-1 and 6100 s-1. Initial results for PMMA have been reported [Forrester/Swallowe 2009]. The rate of strain where specimens begin to show crazing is identified. The value of yield stress increases with the increase of strain rate and the decrease in temperature. Large strain hardening can be seen in all three semi-crystalline polymers at higher strain rates. The temperature rise during plastic flow of compression is calculated by the stress-strain rate curves. In this thesis, the emphasis is on the relation of yield/flow stress to strain rate as the polymers deform under high strain compression. The mechanism behind the cause of high strain rate deformation responses for amorphous to semi-crystalline polymers in ductile state is discussed, with a view to understanding the sensitivity of yield/flow stresses as a function of strain rate. Also, the modelling of the polymers has been carried in order to alleviate doubts about the validity of the real experimental results that may arise due to the nature of the decomposition of the polymers. It has been shown that the strain energy density pulses through the sample in response to the compression wave in various circular intensities.
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Cassino, Theresa R. "Investigation of Cellular Responses Activated by Mechanical Compression in Equine Chondrocytes: Device Design, Construction and Testing." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/26018.
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The metabolic activity of cartilage cells (chondrocytes) is regulated by mechanical forces which act on them. Chondrocytes can respond to these forces through synthesis or degradation of extracellular matrix and changes in gene expression. The overall objective of this study was to investigate the effects of mechanical compression on gene regulation, proteoglycan (PG) synthesis and activation of signaling pathways.
To achieve this goal a simple oscillatory displacement controlled device was designed to provide uniaxial unconfined strain to cell constructs. Static compression and dynamic compression with various waveforms are utilized with a stroke range of 0.25 mm to 4 mm and a frequency range of 0.1 Hz to 3 Hz. Poly-L-lactic acid (PLLA/)alginate disks and alginate disks with equine chondrocytes embedded in them were developed and showed unchanged viability for 24 hr under static and dynamic compression. Testing to relate the strains applied to forces experienced in cell constructs was completed and the simple procedure outlined for companion use with our device.
Quantitative reverse transcription polymerase chain reaction (QRT-PCR) revealed changes in expression of collagen II and matrix metalloproteinase-3 under dynamic compression for 24 hr. Equine chondrocytes compressed for 48 hr showed lower PG synthesis for both static and dynamic compression when compared to uncompressed samples in replicate experiments. Repeatability of this experiment was problematic possibly due to decreased viability and inefficient extraction. Different patterns of extracellular signal regulated kinase (ERK) activation with time were found for uncompressed and compressed samples (static at 15% strain and dynamic at 15% strain, 1 Hz) and protein kinase B (also called Akt) was not regulated by compression. Results from experiments involving frequency and strain for dynamic compression were inconclusive.
These studies show that regulation of gene expression, PG synthesis and intracellular signaling can be studied with our device but optimization of the experimental procedure is still needed. To our knowledge these studies are the first to show these types of studies utilizing equine chondrocytes. Despite issues encountered, our studies provide valuable insights into the effects of compression on equine chondrocytes and detail a simple device for use in a wide variety of compression studies.Ph. D.
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Saarimäki, Jonas. "The mechanical properties of lattice truss tructures with loadbearing shells made of selectively laser melted Hastelloy X (TM)." Thesis, KTH, Industriell produktion, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-41320.
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This thesis discusses how to test the mechanical properties of openlattice truss structures and hybrids being a tube containing a latticetruss structure. By properties we mean strength, stiffness, thermalconductivity and so forth.Mechanical testing was done on two different structures to betterunderstand how the load-bearing properties change when these structuresare subjected to tensile, compressive and bending forces. The structuresinvestigated were Diamond and Octagon built at 45° and 90°. Acousticemission was also used to evaluate and analyze the different behaviour ofthe structures. The test results were used to produce design criteria forproperties in different cell structures manufactured of Hastelloy X™. Amap with design criteria containing stiffness and weight per cubiccentimetre was produced for parts that would be subjected to compressiveforces.
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Sunny, George Padayatil. "High Strain-Rate Compression Behavior of a Zr-based Bulk Metallic Glass." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1190750537.
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Pour, Shahid Saeed Abadi Parisa. "Mechanical behavior of carbon nanotube forests under compressive loading." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47699.
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Carbon nanotube (CNT) forests are an important class of nanomaterials with many potential applications due to their unique properties such as mechanical compliance, thermal and electrical conductance, etc. Their deformation and failure in compression loading is critical in any application involving contact because the deformation changes the nature of the contact and thus impacts the transfer of load, heat, and charge carriers across the interface. The micro- and nano-structure of the CNT forest can vary along their height and from sample to sample due to different growth parameters. The morphology of CNTs and their interaction contribute to their mechanical behavior with change of load distribution in the CNT forest. However, the relationship is complicated due to involvement of many factors such as density, orientation, and entanglement of CNTs. None of these effects, however, are well understood. This dissertation aims to advance the knowledge of the structure-property relation in CNT forests and find methodologies for tuning their mechanical behavior. The mechanical behavior of CNT forests grown with different methodologies is studied. Furthermore, the effects of coating and wetting of CNT forests are investigated as methods to tailor the degree of interaction between CNTs. In situ micro-indentation of uncoated CNT forests with distinct growth-induced structures are performed to elucidate the effects of change of morphology along the height of CNT forests on their deformation mechanism. CNT aerial density and tortuosity are found to dictate the location of incipient deformation along height of CNT forests. Macro-compression testing of uncoated CNT forests reveals mechanical failure of CNT forests by delamination at the CNT-growth substrate. Tensile loading of CNT roots due to post-buckling bending of CNTs is proposed to be the cause of this failure and simple bending theory is shown to estimate the failure load to be on the same order of magnitude as experimental measurements. Furthermore, delamination is observed to occur in the in situ micro-indentation of CNT forests coated with aluminum on the top surface, which demonstrates the role of the mechanical constraints within the CNT forest in the occurrence of delamination at the CNT-substrate interface. In addition, this dissertation explores the mechanical behavior of CNT forests coated conformally (from top to bottom) with alumina by atomic layer deposition. In situ micro-indentation testing demonstrates that the deformation mechanism of CNT forests does not change with a thin coating (2 nm) but does change with a sufficiently thick coating (10 nm) that causes fracturing of the hybrid nanotubes. Ex situ flat punch and Berkovich indentations reveal an increase in stiffness of the CNT forests that are in range with those predicted by compression and bending theories. An increase in the recoverability of the CNTs is also detected. Finally, solvent infiltration is proposed as a method of decreasing stiffness of CNT forests and changing the deformation mechanism from local to global deformations (i.e., buckling in the entire height). Presence of solvents between CNTs decreases the van der Waals forces between them and produces CNT forests with lower stiffness. The results demonstrate the effect of interaction between CNTs on the mechanical behavior. This dissertation reveals important information on the mechanical behavior of CNT forests as it relates to CNT morphology and tube-to-tube interactions. In addition, it provides a framework for future systematic experimental and theoretical investigations of the structure-property relationship in CNT forests, as well as a framework for tuning the properties of CNT forests for diverse applications.
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Foscan, Tiziana. "Mechanical characterization of double-wythe masonry walls with a view to in-situ testing methods." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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Unreinforced masonry is one of the most commonly used structure typologies for the construction of residential buildings, which is why the estimation of its mechanical parameters is of primary importance. The main techniques to acquire them are based on destructive methods, however less invasive tests have been studied in the past years in order to obtain the same parameters in-situ: the core testing method is one of those. While monotonic compression tests on single-wythe cores provided good results, tests performed on double-wythe cores have given a significant overestimation of the compressive strength, supposedly due to the excessive stiffness of the high strength mortar cap used to perform the tests, that doesn’t allow the opening of the collar joint. An experimental campaign was conducted at Delft University of Technology in order to identify a new configuration of the cap suitable to use in moderately destructive tests to retrieve the mechanical properties of masonry under compression. An initial Finite Element Analysis is performed to anticipate the behaviour of the different configurations in order to choose the right prototypes. Four different models are developed, and the most significant ones are implemented and tested in the laboratory. In particular, a configuration with high strength mortar cap is tested as a comparison with previous tests on double-wythe cores, while a configuration with a high strength mortar cap separated from the core by a neoprene sheet is chosen in an attempt to reduce the confinement in the direction perpendicular to the collar joint. Finally the results obtained from the monotonic compression tests on cores are compared with the results from destructive tests on companion wallets, which were carried out in a previous experimental campaign on the same masonry.
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Piao, Kun. "An Elevated-Temperature Tension-Compression Test and Its Application to Mg AZ31B." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316096630.
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Sangle, Sagar Dilip. "Design and Testing of Scalable 3D-Printed Cellular Structures Optimized for Energy Absorption." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1495467365594915.
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Lantz, Josephine. "Mechanical Properties of Calcium Phosphate and Additively Manufactured Titanium Alloy for Composite Spinal Implants." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-296636.
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One of the major health problems in western societies is back pain, with a prevalence rate of 49%–80%. In many cases, the back pain is due to degenerated discs. The gold standard to treat a severely degenerated disc is spinal fusion, where the vertebral disc is replaced with a cage structure. However, fusion cages have a failure rate of 30%, hence the need for further development. The focus of this thesis is to evaluate the combination of calcium phosphate cement with titanium, for a spinal application. Mechanical tests in the form of tensile, compression and 4-point-bending were performed to study the different material properties. The obtained results was applied as material parameters for isotropic linear elastic material models, using ANSYS. This was then used to develop a cage design through topology optimisation which was further evaluated by using Finite Element Analysis. From the tensile testing of the titanium, isotropic behaviour was found. It was also found that a longer mixing time of the cement resulted in poorer mechanical properties of the calcium phosphate, however, no conclusive results were obtained from the 4-point-bending tests. The final cage geometry filled with calcium phosphate was tested under compression to see whether the cage could protect the calcium phosphate or not. MicroCT after the test confirmed that no larger cracks developed during the testing, suggesting that the cage is strong enough to protect the calcium phosphate from mechanical failure.
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He, Wei. "Mechanical and microstructural properties of thin metal films on compliant substrates." Thesis, Poitiers, 2016. http://www.theses.fr/2016POIT2280/document.
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Le comportement mécanique de films minces métalliques déposés sur des substrats souples joue un rôle déterminant dans les performances de l'électronique flexible et des micro- systèmes électromécaniques (MEMS).Dans un premier temps, une nouvelle méthode est présentée pour caractériser le module d'élasticité de films minces submicroniques. Avec deux couches déposées de chaque côté et sur la moitié du substrat polymère, la corrélation d'image numérique (CIN) a été utilisée pour mesurer simultanément la déformation du film et du substrat in situ au cours d'un essai de traction. La différence entre les déformations mesurées sur la partie vierge et le composite permet d'extraire les propriétés élastiques de films minces de manière simple et avec grande précision. Comme attendu, la distribution des déformations est uniforme au travers de l'épaisseur du film ce qui indique une adhésion parfaite entre le film et le substrat. Dans le cas de films minces de tungstène, de chrome, de nickel et de cuivre, les valeurs de module obtenues sont proches de celles des mêmes matériaux à l'état massif.Dans un deuxième temps, une nouvelle méthode expérimentale utilisant une machine de déformation uniaxiale est présentée pour étudier l'effet Bauschinger dans des films minces métalliques déposés sur des substrats étirables. Grâce à un dispositif original, les films minces sont déposés sur des substrats prétendus et peuvent donc être déformés alternativement en tension et en compression dans un large domaine de déformations. La déformation élastique intra granulaire des films minces polycristallins et la déformation macroscopique du substrat sont mesurées in situ par diffraction des rayons X et CIN respectivement. A partir des courbes « déformation élastique – déformation macroscopique », la réponse mécanique de l'ensemble film / substrat est analysée au vu de l'histoire complète du chargement et de la microstructure (contraintes résiduelles, texture) des films mincesThe mechanical behavior of metallic thin films deposited on soft substrates plays a crucial role in the performance of flexible electronics and MicroElectroMechanical Systems (MEMS).At first, a novel method is presented to characterize the in-plane elastic modulus of sub micrometer thin films. With two coating layers bonded symmetrically to half polyimide substrates, Digital Image Correlation (DIC) has been employed to measure time-resolved full-field strain maps of film and substrate during in situ tensile testing. The strain differences between virgin and composite parts allowed to extract the elastic properties of the thin films in a simple way with high precision. As expected, the strain distribution is uniform through the film thickness which indicates a perfect adhesion between the film and the substrate. In the case of tungsten, chromium, nickel and copper films, the values obtained are close to the bulk one.In a second step, a new experimental method using uniaxial tensile testing is presented to study Bauschinger effect in thin metallic films deposited on stretchable substrates. Thanks to our new pre-tensile setup (specific grips), the thin films were deposited on pre-stretched substrates and thus could be deformed alternately in tension and compression within a large strain domain. The elastic intra-granular strain of polycrystalline thin films and true strain of substrates are measured in situ by X-Ray Diffraction (XRD) and DIC. From lattice strain-true strain curves, the mechanical response of copper and nickel /substrate sets is analyzed in view of the complete loading history and the presence of residual stresses and crystallographic texture in thin films
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Al, Rifaie Mohammed Jamal. "Resilience and Toughness Behavior of 3D-Printed Polymer Lattice Structures: Testing and Modeling." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1502760172343413.
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Dean, Maureen A. "Predictions of Distal Radius Compressive Strength by Measurements of Bone Mineral and Stiffness." Ohio University Art and Sciences Honors Theses / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ouashonors1461595642.
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Davidson, Craig. "Investigating the suitability of laser sintered elastomers for running footwear applications." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/11965.
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The research contained within this thesis formed part of an Engineering and Physical Sciences Research Council (EPSRC) funded project based at Loughborough University, which aimed to investigate the use of additive manufacturing (AM), and in particular sintering technologies, for the production of running footwear sole units. Laser sintering (LS) is an AM process which produces parts directly from a computer aided design (CAD) file by selectively fusing successive layers of powdered material using a CO2 laser. LS imparts significant advantages over traditional manufacturing techniques including extensive design freedom, the ability to manipulate the local properties of a single material part as well as economical manufacture of bespoke items due to the elimination of tooling. Modifying the mechanical properties and/or geometry of sole units has been shown to provide benefits in the areas of performance, injury risk reduction and comfort, especially when considering elite athletes on a subject specific basis. Given the attributes of LS outlined above, the technology offers significant potential to produce sole units offering high added-value compared to conventional counterparts which are limited by the constraints of traditional processing techniques such as injection moulding. However, the mechanical capacity of LS polymers in context of such application was unknown. Accordingly, this research investigated the suitability of a laser sintered elastomer (LSE) material, in view of key selected mechanical properties, for the manufacture of running shoe midsoles. The midsole is the primary functional component in the sole unit of a running shoe used for distance running on hard surfaces. Following a preliminary assessment of the selected LSE (TPE 210-S), a new dynamic test method was designed to assess the compressive, fatigue and time dependent recovery properties of midsole material specimens under loading conditions representative of in-service use. The method was successfully implemented on an electro-mechanical test apparatus (previously unreported upon in literature) and used firstly, to benchmark the aforementioned properties of a range of ethylene vinyl acetate (EVA) and polyurethane (PU) midsole foams representative of the range currently used in production, and secondly, to establish the same property set for TPE 210-S specimens produced across a range of laser powers (LP's). Initial cycle operating ranges in terms of key compressive properties were established for EVA and PU materials. All conventional variants showed considerable deterioration from these initial values over the 125,000 cycle test regime, but subsequently demonstrated partial recovery when left unloaded post-test. PU grades generally exhibited better fatigue performance and findings were consistent with those of previous studies. Whilst variation in LP facilitated linear variation in displacement and stiffness properties for TPE 210-S, all specimens yielded a stiffer and more elastic response than that of conventional foams at the outset; initial compressive operating ranges, whilst within close proximity, did not overlap. However, fatigue performance was found to be superior with only relatively small property changes occurring over the test regime regardless of LP. Furthermore, no signs of catastrophic specimen failure (e.g. cracking) were visually apparent. In this respect the material showed good suitability for midsole applications, but further work is required to address increasing the available compressive property range which fell outside the scope of this work.
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Bourguignon, Átila Sala. "Caracterização de concreto reforçado com fibras pela técnica de microtomografia computadorizada por transmissão de raios X." Universidade do Estado do Rio de Janeiro, 2011. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=3088.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorNesta dissertação de Mestrado do programa de Pós-Graduação em Ciência e Tecnologia dos Materiais é apresentado um estudo para a caracterização do concreto reforçado com fibras de polipropileno e de aço pela análise das imagens de microtomografia computadorizada por transmissão de raios X (μCT). Foram produzidos corpos de prova de concreto para determinar a sua resistência mecânica à compressão. As imagens foram obtidas no sistema Skyscan, modelo 1174, reconstruídas e analisadas. Foi possível observar na análise das imagens a estrutura da fibra de aço dispersa na matriz do concreto e quantificá-las pelo programa de análise de imagens Ctan e perceber um ganho na resistência mecânica em relação ao concreto sem fibras. Não foi feito a quantificação das amostras de fibras de polipropileno dispersas na matriz de concreto, mas foi observada a presença de aglomerados dessa fibra que resultaram na perda da resistência mecânica em relação ao concreto sem fibras.
In this dissertation Masters Program Graduate in Science and Technology of Materials is presented a study for characterization of concrete reinforced with polypropylene fibers and steel by image analysis of computed microtomography X ray transmission (μCT). Concrete samples were produced to determine their mechanical resistance to compression. The images were obtained in the SkyScan model 1174, reconstructed and analyzed. It was possible, in image analysis, to observe the structure of steel fiber dispersed in the concrete matrix and quantify them by image analysis program Ctan and observed a gain in strength compared to concrete fiber less. The quantification was not did to samples of polypropylene fibers dispersed in the matrix of concrete, but we observed the presence of clusters fibers resulting in the loss of mechanical strength compared to concrete fiber less.
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Evans, T. Matthew. "Microscale Physical and Numerical Investigations of Shear Banding in Granular Soils." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7576.
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Under loading conditions found in many geotechnical structures, it is common to observe failure in zones of high localized strain called shear bands. Existing models predict these localizations, but provide little insight into the micromechanics within the shear bands. This research captures the variation in microstructure inside and outside of shear bands that were formed in laboratory plane strain and two-dimensional discrete element method (DEM) biaxial compression experiments.
Plane strain compression tests were conducted on dry specimens of Ottawa 20-30 sand to calibrate the device, assess global response repeatability, and develop a procedure to quantitatively define the onset of localization. A new methodology was employed to quantify and correct for the additional stresses imparted by the confining membrane in the vicinity of the shear band. Unsheared and sheared specimens of varying dilatancy were solidified using a two-stage resin impregnation procedure. DEM tests were performed using an innovative servo-controlled flexible lateral confinement algorithm to provide additional insights into laboratory results.
The solidified specimens were sectioned and the resulting surfaces prepared for microstructure observation using bright field microscopy and morphological analysis. Local void ratio distributions and their statistical properties were determined and compared. Microstructural parameters for subregions in a grid pattern and along predefined inclined zones were also calculated. Virtual surfaces parallel to the shear band were identified and their roughnesses assessed. Similar calculations were performed on the DEM simulations at varying strain levels to characterize the evolution of microstructure with increasing strain.
The various observations showed that the mean, standard deviation, and entropy of the local void ratio distributions all increased with increasing strain levels, particularly within regions of high local strains. These results indicate that disorder increases within a shear band and that the soil within the shear band does not adhere to the classical concept of critical state, but reaches a terminal void ratio that is largely a function of initial void ratio. Furthermore, there appears to be a transition zone between the far field and the fully formed shear block, as opposed to an abrupt delineation as traditionally inferred.
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Stellmar, Justin. "Predicting the Deformation of 3D Printed ABS Plastic Using Machine Learning Regressions." Youngstown State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1587462911261523.
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Arshad, Mubeen. "Damage tolerance of 3D woven composites with weft binders." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/damage-tolerance-of-3d-woven-composites-with-weft-binders(2b1435bc-fdb7-47c3-b555-ca5ea2883b4b).html.
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3D woven composites, due to the presence of through-thickness fibre bridging, have the potential to improve damage tolerance and at the same time to reduce the manufacturing costs. However, the ability to withstand damage depends on weave architecture as well as the geometry of individual tows. A substantial amount of research has been performed to understand in-plane properties as well as the performance of 3D woven composites exposed to impact loads, but there is limited research on the damage tolerance and notch sensitivity of 3D weaves and no work is reported on the damage tolerance of 3D weaves with a weft binding pattern. In view of the recent interest in 3D woven composites, the influence of weft binder on the tensile, open hole tensile, impact resistance and subsequent residual compressive strength properties and failure mechanisms of 3D woven composites was investigated against equivalent UD cross-ply laminate. Four different 3D woven architectures; layer-to-layer, angle interlocked, twill angle interlock and modified angle interlock structures were produced under identical weaving conditions. All the above mentioned tests were performed in both the warp and weft directions on 3D woven and UD cross-ply laminates. Stress concentration and yarn waviness due to through-thickness reinforcement led to lower mechanical properties compared with the UD cross-ply laminate. However, improved in-plane and damage tolerance properties of 3D woven composites under tensile loads were achieved by modifying the weave architecture. The influence of the weave architecture and binder yarn orientation on the notch insensitivity and damage tolerance of 3D woven composites was less significant for compressive loads. Despite the lower undamaged compression strength of 3D woven structures, their residual compressive strength was found to be superior to their equivalent UD cross-ply laminates. The lower rate of strength reduction in the 3D woven fabrics laminates was attributed to a crack bridging mechanism, effectively inhibiting delamination propagation.
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Farahat, Waleed A. (Waleed Ahmed) 1975. "Dynamical characterization, state estimations and testing of active compressor blades." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/89267.
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Niu, Kangmin. "Compressive behavior of sandwich panels and laminates with damage." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/12056.
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Reinhart, Justin. "Design of a Small-Turbjojet Compressor Test Facility." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1627646764402806.
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Olmedo, Reynaldo A. "Compression and buckling of composite panels with curvilinear fibers." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-08142009-040516/.
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Hahn, Steven Eric. "An experimental/analytical investigation of combined shear/end loaded compression strength testing of unidirectional composites." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-12232009-020534/.
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Shultz, Jacque. "Authenticating turbocharger performance utilizing ASME performance test code correction methods." Thesis, Kansas State University, 2011. http://hdl.handle.net/2097/8451.
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Master of ScienceDepartment of Mechanical and Nuclear Engineering
Kirby S. Chapman
Continued regulatory pressure necessitates the use of precisely designed turbochargers to create the design trapped equivalence ratio within large-bore stationary engines used in the natural gas transmission industry. The upgraded turbochargers scavenge the exhaust gases from the cylinder, and create the air manifold pressure and back pressure on the engine necessary to achieve a specific trapped mass. This combination serves to achieve the emissions reduction required by regulatory agencies. Many engine owner/operators request that an upgraded turbocharger be tested and verified prior to re-installation on engine. Verification of the mechanical integrity and airflow performance prior to engine installation is necessary to prevent field hardware iterations. Confirming the as-built turbocharger design specification prior to transporting to the field can decrease downtime and installation costs. There are however, technical challenges to overcome for comparing test-cell data to field conditions. This thesis discusses the required corrections and testing methodology to verify turbocharger onsite performance from data collected in a precisely designed testing apparatus. As the litmus test of the testing system, test performance data is corrected to site conditions per the design air specification. Prior to field installation, the turbocharger is fitted with instrumentation to collect field operating data to authenticate the turbocharger testing system and correction methods. The correction method utilized herein is the ASME Performance Test Code 10 (PTC10) for Compressors and Exhausters version 1997.
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Wasserbauer, Jaromír. "Mechanické vlastnosti mikrostrukturních komponent anorganických materiálů." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2013. http://www.nusl.cz/ntk/nusl-233368.
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Disertační práce se zabývá studiem strukturních a mechanických vlastností anorganických materiálů. Cílem je nalezení jednotlivých fází ve zkoumaném materiálu a hlavně lokalizace (mechanicky) nejslabšího místa, jeho ovlivnění a následně výroba materiálu o lepších mechanických vlastnostech. Z důvodu velkého množství použitých metod je základní teorie vložena vždy na začátku příslušné kapitoly. Taktéž z důvodu značného množství výsledků jsou na konci kapitol uvedeny dílčí závěry. Práce je rozdělena na tři části, kdy první se zabývá seznámením s možnostmi modelování mikro-mechanických vlastností a provedením experimentů umožňujících posouzení rozsahu platnosti některého modelu. V druhé části je provedeno shrnutí současných možností indentačních zkoušek pro měření mechanických vlastností strukturních složek betonu a praktické zvládnutí metodiky vhodné k užití pro výzkum materiálů zkoumaných domovským pracovištěm. V třetí části je navržena metoda identifikace nejslabších článků struktury anorganických pojiv a její ověření na konkrétním materiálu zkoumaném na domovském pracovišti. V této dizertační práci jsou použity tyto metody: kalorimetrie, ultrazvukové testování, jednoosá pevnost v tlaku, nanoindentace, korelativní mikroskopie a rastrovací elektronová mikroskopie s energiově disperzním spektrometrem. Dílčími výsledky jsou kompletní charakterizace cementových materiálů, upřesnění stávajících poznatků a nalezení optimálního postupu pro charakterizaci. Hlavním výsledkem je inovativní přístup vedoucí k pozitivnímu ovlivnění materiálu.
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Struwig, Daniel Johannes. "The development and verification of a centrifugal compressor test bench." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86250.
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Thesis (MScEng)--Stellenbosch University, 2014.ENGLISH ABSTRACT: Turbomachinery plays an important role in the efficiency of power generation and combustion processes used in the automotive and aerospace industries. The potential for fulfilling future energy needs has been identified in both civilian and military applications, for example micro gas turbines (MGTs) used in unmanned aireial vehicles (UAVs). The goal of this thesis was to build a performance testing facility for small-scale centrifugal compressors, for use in MGTs. The objectives of this study were mainly achieved through experimental work. In addition to the experimental work, numerical simulations using computational fluid dynamics (CFD) software were performed to substantiate the experimental results. The project methodology followed the process whereby a compressor performance map is constructed from experimental data and compared to map obtained from theoretical data. The test facility consists of a turbocharger fitted with an experimental compressor section. The turbocharger turbine is driven by unheated compressed air. Sensors, data acquisition and ancillary equipment required to perform performance test measurements, were obtained and installed on the test facility. Performance curves at three different rotational speeds were successfully obtained for the experimental compressor. When compared to the CFD results there was good qualitative agreement, although deviations in the results increased with rotational speed. In addition a second impeller design was tested which correlated well with the theoretical data.
AFRIKAANSE OPSOMMING: Turbomasjinerie speel 'n belangrike rol in die doeltre endheid van kragop- wekking en verbrandingsprosesse wat in die motor- en lugvaartbedryf gebruik word. Die potensiaal om in toekomstige energiebehoeftes te voorsien is in beide burgerlike en militêre toepassings uitgewys, byvoorbeeld mikrogastur- bines (MGT's) wat in onbemande vliegtuie (OLV's) gebruik word. Die doel met hierdie tesis was om 'n prestasietoetsfasiliteit vir kleinskaalse sentrifu- gale kompressors te bou wat in MGT's gebruik kan word. Die doelstellings van hierdie studie is hoofsaaklik deur eksperimentele werk behaal. Daarbe- newens is numeriese simulasies met gebruikmaking van sagteware vir bereke- ningsvloeidinamika (BVD) gedoen om die eksperimentele resultate te staaf. Die projekmetodologie volg die proses om 'n kompressorprestasiekaart uit eks- perimentele data op te stel en dit te vergelyk met 'n kaart wat uit teoretiese data bekom is. Die toetsfasiliteit bestaan uit 'n turboaanjaer wat met 'n eksperimentele kompressordeel toegerus is. Die turboaanjaer se turbine word deur onverhitte druklug aangedryf. Sensors, dataverwerwing en bykomstige toerusting, wat benodig is om prestasietoetsmetings mee te doen, is bekom en op die toetsfasiliteit geïnstalleer. Prestasiekrommes is vervolgens by drie verskillende omwentelingsnelhede suksesvol met die eksperimentele kompres- sor bekom. In vergelyking met die BVD-resultate was daar goeie kwalitatiewe ooreenstemming, ofskoon afwykings in die resultate vergroot het namate die omwentelingspoed toegeneem het. Daarby is 'n tweede stuwerontwerp getoets wat goed met die teoretiese resultate korreleer.
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Brandsen, Jacobus Daniel. "Prediction of axial compressor blade vibration by modelling fluid-structure interaction." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85616.
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Thesis (MScEng)-- Stellenbosch University, 2013.ENGLISH ABSTRACT: The Council for Scientific and Industrial Research has developed a vibration excitation system. The system is designed to excite the rotor blades of an axial compressor in the specified vibration mode and at the specified frequency. The vibration excitation system was tested on Stellenbosch University’s Rofanco compressor test bench. A two-way staggered fluid-structure interaction (FSI) model was created that was capable of simulating the vibration of the rotor blades excited by the system. The results of the FSI model were verified using available experimental data. It was concluded that the FSI model is able to recreate the vibration excited by the system to within the desired level of accuracy. In addition, the results of the FSI model showed that the vibration excitation system should be able to excite the blades in the selected vibration mode and at the selected frequency provided that the excitation frequency is close the natural frequency of the first bending mode. The results also suggested that a transient computational fluid dynamics model should be sufficient for the prediction of the aerodynamic forces acting on the rotor blades. Furthermore, a one-way staggered FSI model should be adequate for calculating the motions of the blades.
AFRIKAANSE OPSOMMING: Die Wetenskaplike en Nywerheidnavorsingsraad het ’n vibrasie-opwekkingstelsel ontwerp om die rotorlemme van ’n aksiaalvloei kompressor in die gespesifiseerde vibrasiemodus en teen die gespesifiseerde frekwensie op te wek. Die vibrasieopwekkingstelsel is met behulp van die Universiteit Stellenbosch se Rofanco kompressortoetsbank getoets. Daarna is ’n tweerigting vloeistof-struktuur-interaksie model geskep om die vibrasie van die rotorlemme, wat deur die stelsel opgewek is, te simuleer. Beskikbare eksperimentele data is gebruik om die resultate van die vloeistof-struktuur-interaksie model te bevestig. Die gevolgtrekking is gemaak dat die model wél die vibrasie van die lemme met die nodige akkuraatheid kan simuleer. Die resultate van die vloeistof-struktuur-interaksie model toon ook dat die stelsel die lemme in die gekose vibrasiemodus en teen die gekose frekwensie behoort te kan opwek, solank die opwekkingsfrekwensie na aan die natuurlike frekwensie van die eerste buigmodus is. Voorts dui die resultate daarop dat ’n berekeningsvloeimeganika model die aërodinamiese laste van die lemme sal kan voorspel. ’n Eenrigting vloeistof-struktuur-interaksie model behoort voldoende te wees om die beweging van die rotorlemme te bereken.
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Boussetta, Abid Hajer. "Caractérisation expérimentale par émission acoustique et modélisation numérique du comportement des structures composites obtenues par enroulement filamentaire." Thesis, Compiègne, 2019. http://www.theses.fr/2019COMP2519.
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De nos jours, les tubes composites obtenus par enroulement filamentaire PRV, sont largement utilisés dans le domaine de transport des fluides. Cependant, pour le concepteur, ces nouveaux matériaux représentent un changement important, qui impacte profondément la conception, et la réalisation des produits industriels. Pour bien prendre la mesure de ce changement, il est essentiel de bien appréhender les particularités mécaniques de ce matériau à travers des essais expérimentaux. Ce qui a fait l’objet des travaux de cette thèse. Plusieurs techniques et outils ont été donc utilisés, en particulier la technique de l’émission acoustique. Cette étude de caractérisation a permis la modélisation numérique du comportement du matériau. Lors du développement du modèle, un ensemble de paramètres a été utilisé dont l’identification a nécessité l'utilisation de dispositifs expérimentaux spéciaux, en plus de l’outil numérique. Ce modèle a été validé grâce à une comparaison avec des essais de traction et de compression sur des éprouvettes représentatives. Ce qui a ouvert la voie, à l’utilisation de ce modèle dans une application industrielle par la simulation d’un essai de mise sous pression d’un tubeNowadays, filament wound composite pipes GRP, are widely used in in the transport of fluids. However, for the designer, these new materials represent a significant change, which profoundly affects the design and realization of industrial products. In order to take the measure of this change, it is essential to understand the mechanical characteristics of this material through experimental tests; which is the purpose of this thesis works. Thus, several techniques and tools have been used, in particular the acoustic emission technique. This experimental characterization study allowed the numerical modeling of the material behavior. During the development of the model, a set of parameters is involved; whose identification has required the use of special experimental devices, in addition to the numerical tool. The model has been validated by comparison with tensile and compressive tests on representative specimens. This paved the way for the use of this model in an industrial application by modeling a test of pipe pressurizing
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GALDINO, JÚNIOR Francisco. "Desenvolvimento de uma máquina de impacto por queda de peso para materiais compósitos." Universidade Federal de Campina Grande, 2014. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/491.
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FRANCISCO GALDINO JÚNIOR - DISSERTAÇÃO PPGEM 2014..pdf: 6213176 bytes, checksum: 50d50ccb2736f335fb4e52475cb149f7 (MD5)Made available in DSpace on 2018-04-25T15:51:00Z (GMT). No. of bitstreams: 1 FRANCISCO GALDINO JÚNIOR - DISSERTAÇÃO PPGEM 2014..pdf: 6213176 bytes, checksum: 50d50ccb2736f335fb4e52475cb149f7 (MD5) Previous issue date: 2014-08-28
O crescente desenvolvimento de materiais compósitos reforçados nos últimos anos tem propiciado novas alternativas para solucionar diversos problemas acerca da necessidade de novos materiais com combinações de propriedades. Para utilizarmos tais materiais, devemos realizar vários ensaios mecânicos, como: tração, compressão, flexão e principalmente de impacto. Para isso, foram realizados estudos específicos sobre materiais compósitos e impactos em estruturas laminadas. Através desses estudos e de um levantamento do estado da arte acerca do projeto de diversas máquinas de impacto por queda de peso, foi projetada e fabricada uma máquina de impacto por queda de peso para materiais compósitos de simples concepção. A máquina desenvolvida possui um intervalo de energia de impacto entre 20J e 96J, obtida através de variação da massa de queda de impacto. Foi desenvolvido também um sistema instrumentação para aquisição da força de impacto e da energia absorvida pelo corpo de prova, além de um sistema anti rebote eletromecânico. Para a validação do equipamento foram realizados ensaios de impacto por queda de peso em placas compósitas de fibra de vidro com 8, 10, 12 e 14 camadas e analisado os danos causados nas mesmas, através de software de análise de imagem. A partir de um software de análise de vídeo foi possível calcular a velocidade de impacto e a energia de impacto nos ensaios e comparar com o método teórico e o instrumentado.
The increasing development of reinforced composite materials in recent years has provided new alternatives to solve various problems about the need for new materials with combinations of properties. For such materials we use, we conduct various mechanical tests, such as tensile, compression, bending and mainly impact. For this, specific studies on composite materials, and impact on laminate structures were performed. Through these studies and a survey of state of the art about the project in several of drop impact weight machines, is designed and manufactured a machine to drop impact weight for composites of simple design. The machine has developed a range of impact energy of 20J, and 96J, obtained by varying the mass of the drop impact. One instrumentation system for the acquisition of the impact force and energy absorbed by the specimen was also developed, and an anti rebound electromechanical system. To validate the equipment impact tests were performed by weight loss in composite plates with glass fiber 8, 10, 12 and 14 layers and analyzed the damage caused in the same via image analysis software. From a software video analysis it was possible to calculate the impact velocity and impact energy in the tests and compare with the theoretical method and instrumented.
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Orgéas, Laurent. "Étude expérimentale et numérique du comportement thermomécanique d'un alliage à mémoire de forme industriel NiTi." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10256.
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Le present document est une contribution a l'etude experimentale, theorique et numerique du comportement thermomecanique d'un alliage a memoire de forme industriel niti. Le travail est constitue principalement de trois parties : validation des hypotheses de base utilisees dans les lois de comportement, realisation d'essais mecaniques pour caracteriser les comportements ferroelastique et superelastique du materiau, et modelisation tridimensionnelle appliquee au calcul de structures. L'objectif d'un tel travail est de fournir a l'ingenieur de bureau d'etudes un outil numerique capable de dimensionner des pieces de structures en alliages a memoire de forme. Les lois de comportement sont etablies a partir d'hypotheses physiques, en particulier concernant l'origine de l'hysteresis tant thermique que mecanique. Celles-ci sont validees a partir d'experiences realisees en cisaillement simple en ferroelasticite et en superelasticite, sur des polycristaux de niti, mais aussi sur des monocristaux de cuznal. De plus, les predictions quantitatives du modele sont alors satisfaisantes. Une campagne d'essais homogenes de caracterisation (traction, compression et cisaillement) est effectuee a differentes temperatures. Ces essais ont ete realises sur des toles ayant ete soumises au meme traitement thermomecanique prealable. Ils mettent en evidence la complexite des phenomenes physiques a modeliser : comportement fortement non lineaire a hysteresis, dependance des proprietes caracteristiques avec la temperature, dissymetrie de comportement entre traction et compression. Le schema constitutif sous sa forme tridimensionnelle est alors identifie a ces essais, et modelise correctement la majorite des comportements observes. Ce schema est implante dans un code de calculs elements finis ecrits en grandes transformations, qui utilise la notion de coordonnees materielles entrainees. Finalement, la demarche de modelisation est validee : les predictions des simulations numeriques sont comparees avec des experiences mettant en evidence des sollicitations heterogenes, soit de localisation observee lors de traction de tole, soit de flexion de poutre.
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Gratton, Michel. "Comportement d'un composite 3D carb/carb : méso-modélisation pour la prévision de la réponse sous choc." Cachan, Ecole normale supérieure, 1998. http://www.theses.fr/1998DENS0004.
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Ce travail, mené en collaboration avec l'aérospatiale Les Mureaux et le centre d'études de Gramat, concerne la modélisation de matériaux composites tridirectionnels carbone/carbone sous sollicitations fortement dynamiques. Pour ce type de sollicitations, la notion de matériau homogène équivalent est inadaptée. L'objet de ce travail est de tester l'aptitude d'une modélisation a l'échelle des constituants mésoscopique (torons de fibres et blocs de matrice), a reproduire la réponse du matériau sous choc. Le matériau est tout d'abord identifie a l'échelle de ses méso-constituants. A cette fin, divers essais quasi-statiques sont réalisés et une modélisation sans effet de vitesse du comportement des constituants est alors proposée. Elle prend en compte des mécanismes d'endommagement, de compaction et d'anélasticité. Une technique de changement d'échelle, basée sur les développements asymptotiques adaptée aux matériaux périodiques, est utilisée. Associée à une analyse de sensibilité et à une hiérarchisation des mécanismes non-linéaires, elle permet de déterminer les paramètres locaux du modèle a partir des réponses globales du matériau. Afin de tester le méso-modèle ainsi identifie, une partie des informations est exploitée dans un logiciel de dynamique simplifie. Ce dernier permet de simuler les essais d'impact plaque/plaque suivant une direction de torons. Des essais de compression dynamique et des essais d'écaillage (réalisés par le ceg) sont ainsi bien reproduits. Les simulations montrent des modes distincts de propagation d'ondes dans les torons et dans la matrice ainsi que des phénomènes de transferts de charges. Des essais i pulsionnels, mal reproduits par simulation, ouvrent de nombreuses perspectives, notamment sur la nécessite de compléter la modélisation du comportement des méso-constituants par une sensibilité a la vitesse de déformation.
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Warnock, Corinne Marie. "Process Development for Compression Molding of Hybrid Continuous and Chopped Carbon Fiber Prepreg for Production of Functionally Graded Composite Structures." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1518.
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Composite materials offer a high strength-to-weight ratio and directional load bearing capabilities. Compression molding of composite materials yields a superior surface finish and good dimensional stability between component lots with faster processing compared to traditional manufacturing methods. This experimental compression molding capability was developed for the ME composites lab using unidirectional carbon fiber prepreg composites. A direct comparison was drawn between autoclave and compression molding methods to validate compression molding as an alternative manufacturing method in that lab. A method of manufacturing chopped fiber from existing unidirectional prepreg materials was developed and evaluated using destructive testing methods. The results from testing both the continuous and chopped fiber were incorporated into the design of a functionally graded hybrid continuous and chopped carbon fiber component, the manufacture of which resulted in zero waste prepreg material.
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Reddy, Yeruva S. "Numerical simulation of damage and progressive failures in composite laminates using the layerwise plate theory." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/38534.
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Cluff, Daniel Robert Andrew. "Fabrication of a New Model Hybrid Material and Comparative Studies of its Mechanical Properties." Thesis, 2007. http://hdl.handle.net/10012/3136.
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A novel aluminum foam-polymer hybrid material was developed by filling a 10 pore per inch (0.39
pores per millimeter), 7 % relative density Duocel® open-cell aluminum foam with a thermoplastic
polymer of trade name Elvax®. The hybrid was developed to be completely recyclable and easy to
process. The foam was solution treated, air quenched and then aged for various times at 180˚C and
220˚C to assess the effect of heat treatment on the mechanical properties of the foam and to choose
the appropriate aging condition for the hybrid fabrication. An increase in yield strength, plateau
height and energy absorbed was observed in peak-aged aluminum foam in comparison with underaged
aluminum foam. Following this result, aluminum foam was utilized either at the peak-aged
condition of 4 hrs at 220˚C or in the as-fabricated condition to fabricate the hybrid material.
Mechanical properties of the aluminum foam-polymer hybrid and the parent materials were assed
through uniaxial compression testing at static ( de/dt = 0.008s-1 ) and dynamic ( de/dt = 100s-1 ) loading
rates. The damping characteristics of aluminum foam-polymer hybrid and aluminum foam were also
obtained by compression-compression cyclic testing at 5 Hz. No benefit to the mechanical properties
of aluminum foam or the aluminum foam-polymer hybrid was obtained by artificial aging to peakaged
condition compared to as-fabricated foam. Although energy absorption efficiency is not
enhanced by hybid fabrication, the aluminum foam-polymer hybrid displayed enhanced yield stress,
densification stress and total energy absorbed over the parent materials. The higher densification
stress was indicative that the hybrid was a better energy absorbing material at higher stress than the
aluminum foam. The aluminum foam was found to be strain rate independent unlike the hybrid where
the visco-elasticity of the polymer component contributed to its strain rate dependence. The damping
properties of both aluminum foam and the aluminum foam-polymer hybrid materials were found to
be amplitude dependant with the hybrid material displaying superior damping capability.
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Chaimoon, Krit Civil & Environmental Engineering Faculty of Engineering UNSW. "Numerical simulation of fracture in unreinforced masonry." 2007. http://handle.unsw.edu.au/1959.4/40757.
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The aims of this thesis are to study the fracture behaviour in unreinforced masonry, to carry out a limited experimental program on three-point bending (TPB) masonry panels and to develop a time-dependent fracture formulation for the study of mode I fracture in quasi-brittle materials. A micro-model for fracture in unreinforced masonry is developed using the concept of the discrete crack approach. All basic masonry failure modes are taken into account. To capture brick diagonal tensile cracking and masonry crushing, a linear compression cap is proposed with a criterion for defining the compression cap. The failure surface for brick and brick-mortar interfaces are modelled using a Mohr-Coulomb failure surface with a tension cut-off and a linear compression cap. The fracture formulation, in nonholonomic rate form within a quasi-prescribed displacement approach, is based on a piecewise-linear constitutive law and is in the form of a so-called ?linear complementarity problem? (LCP). The proposed model has been applied to simulating fracture in masonry shear walls and masonry TPB panels. An experimental program was undertaken to investigate the failure behaviour of masonry panels under TPB with relatively low strength mortar. The basic material parameters were obtained from compression, TPB and shear tests on bricks, mortar and brick-mortar interfaces. The experimental results showed that the failure of masonry TPB panels is governed by both tensile and shear failure rather than just tensile failure. The simulation of the masonry TPB tests compared well with the experimental results. In addition, the LCP fracture formulation is enhanced to study the time-dependent mode I fracture in quasi-brittle materials. Two main time-dependent sources, the viscoelasticity of the bulk material and the crack rate dependent opening, are taken into account. A simplified crack rate model is proposed to include the rate-dependent crack opening. The model is applied to predicting time-dependent crack growth in plain concrete beams under sustained loading. The model captures the essential features including the observed strength increase with loading rate, the load-deflection and load-CMOD responses, the deflection-time and CMOD-time curves, the predicted time to failure and the stress distributions in the fracture zone.