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Amini, Ahmad J. "Static and Fatigue Failure Response of Woven Carbon Fiber Specimens with Double Edge Notches." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/425.
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Carbon fiber composites are continually seeing increased use in aerospace applications. It is necessary to understand their failure modes in order to properly design and perform analysis on structures constructed primarily from them. This thesis studies woven carbon fiber composites with and without double-edge notches in a series of static and fatigue tests performed on an Instron 8801 servo-hydraulic testing system.
Specimens were constructed of Advanced Composites Group product # LTM45EL woven carbon fiber pre-preg/epoxy and were cut to approximately 9-inch in length and 1-inch in width. Notches were cut into some of the specimens using a slitting saw blade of 0.006-in. thickness.
Ultimate strength, Young’s modulus and Poisson’s ratio for specimens were determined to be 119,418 psi, 7,149,000 psi and 0.05, respeictively. Fracture stress for specimens with notch depths of 0.10, 0.15, 0.20, 0.25, 0.30 and 0.35 was determined to be 93,481 psi, 88,193 psi, 86,968 psi, 81,112 psi, 84,197 psi and 81,955 psi, respectively. The results from these tests showed that the specimens followed Griffith’s model for brittle failure.
Average number of cycles to failure was determined to be 6,600, 37,200, 94,300 and 293,400 for fatigue tests with maximum stresses of 72.5%, 75%, 77.5% and 80% of the ultimate strength. Fatigue tests performed on notched specimens produced data that was too scattered from which to draw a statistically significant result. Numerical modeling in Abacus showed comparable results to experimental tests for stress and strain.
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Chang, Tsunou. "The notched coating adhesion specimen : a fracture test for coatings and accelerated screening test for adhesion /." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-11182008-063511/.
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Sener, Karakas Sinem. "Shear Mode Rock Fracture Toughness Determination With A Circular Plate Type Specimen Under Three-point Bending." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613036/index.pdf.
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Fracture toughness is an important rock property for rock fracturing and fragmentation applications. Theory and practice of opening mode (mode I) and shearing mode (mode II) fracture toughness tests are still in a developing stage for the cylindrical rock cores. A new circular plate type test specimen is used for mode II fracture toughness testing on rock cores. This involves a straight edge notched circular plate type core disc geometry under three-point bending load<br>new method and its associated specimen geometry is referred as straight edge notched disc bend (SNDB) specimen under three-point bending. Mode II fracture toughness results of the tests with this new geometry were compared to the results of the tests commonly employed for mode II fracture toughness testing.
Specimen geometries were modeled and mode II stress intensity factors were computed by finite element modeling using ABAQUS program. For comparison purposes, mode II or shearing mode fracture toughness KIIc of two different rock types were determined by different testing methods commonly employed in recent practice. Core specimens of Ankara andesite and Afyon marble rock types were tested with cracked chevron notched Brazilian disc and cracked straight through Brazilian disc specimens under Brazilian type loading, semi-circular bend specimen and straight edge notched disc bending specimen geometries under three-point bending.For all testing groups, cylindrical cores with diameters varying from 7.5 cm to 12.5 cm were prepared with notch lengths changing from 1.5 cm to 2.6 cm.
Effect of specimen thickness on mode II fracture toughness was investigated for three different testing methods. Fracture toughness values remained constant when thickness of the specimens was increased for cracked straight through Brazilian disc, semi-circular bend and straight notched disc bend methods. For cracked straight through Brazilian disc method KIIc values of Ankara andesite and Afyon marble were 0.99 MPa&radic<br>m and 0.86 MPa&radic<br>m, respectively. Mode II fracture toughness with semi-circular bend specimen was 0.43 MPa&radic<br>m for andesite and 0.46 MPa&radic<br>m for marble. When the results of the two three-point bending type tests were compared straight notched disc under three-point bending resulted in higher KIIc values (0.61 MPa&radic<br>m for andesite and 0.62 MPa&radic<br>m for marble) than the results found by semi-circular bend tests.
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Schuller, Daniel. "Determinação da tenacidade à fratura do aço aeronáutico 300M, submetido a diferentes parâmetros de tratamentos térmicos e criogenia, utilizando técnica de corpo cilíndrico com entalhe." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-12052016-092247/.
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Foi realizado estudo sobre a influência da variação de alguns parâmetros do tratamento térmico de têmpera e revenimento, bem como aplicação de criogenia, na tenacidade a fratura do aço aeronáutico 300M, com a utilização da técnica de corpo cilíndrico com entalhe. Primeiramente, realizou-se a construção da curva de transição dúctil frágil, através de ensaio Charpy, para amostras submetidas a três tratamentos térmicos, 1 - Têmpera seguida de Revenimento, 2 - Têmpera seguida de criogenia e revenimento. Não foi observada influência significativa da aplicação da criogenia (tratamento de numero 2) na curva de transição dúctil-frágil em comparação com o tratamento térmico número 1. Em um segundo momento, com o auxílio da técnica de ensaio de corpo cilíndrico com entalhe, realizou-se a medição da tenacidade à fratura das amostras do aço 300M submetido a quatro diferentes tratamento térmicos, Q, V, C e D. Os tratamentos variavam entre si principalmente pela temperatura de austenitização. Os valores de dureza para as amostras submetidas a criogenia (V e D) foram maiores que as dos tratamentos sem criogenia (Q e C), e também apresentaram tenacidade à fratura menor. Com relação à temperatura de austenitização, observou-se que os tratamentos C e D, austenitizados a 980°C, propiciaram a completa dissolução de precipitados primários da matriz, elevando a tenacidade à fratura com relação aos tratamentos realizados na faixa de 870°C, Q e V, superando também os efeitos negativos para a tenacidade à fratura devido ao aumento no tamanho de grão.<br>This work studies the influence of the variation for some parameters on quenching and tempering heat treatment, and also deep cryogenic application, on aeronautic steel 300M fracture toughness. First, the ductile-brittle curve was constructed, by Charpy test, for samples submitted for three heat treatments, 1 Quenching and Tempering, 2 Quenching, deep cryogenic and tempering. No significant influence of deep cryogenic treatment addition (heat treatment 2) on ductile-brittle curve was observed in comparison with heat treatment 1. After that, the fracture toughness for 300M steel, submitted for heat treatments Q, V, C e D, was measured using circumferentially notched specimens technique. The main difference among these heat treatments is about austenitizing temperature. For heat treatments with deep cryogenic treatment (V and D), the hardness values were bigger than the ones without this and, analyzing fracture toughness, it was lower than the treatments without cryogenic treatment. Regarding austenitizing temperature, all heat treatments with higher austenitizing temperature at 980°C (C and D), allows complete dissolution of carbides and prior precipitates particles. Its effect was observed that this characteristic increase the fracture toughness when it is compared with others heat treatments with lower austenitizing temperature at 870°C (Q and V). This improvement is enough to overcome the grain size grown negative effects for fracture toughness.
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Ahmad, Haider Yousif. "Fatigue crack growth at notches." Thesis, University of Sheffield, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360410.
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Stehn, Lars. "Fracture toughness of sea ice : development of a test system based on shevron notched specimens." Licentiate thesis, Luleå tekniska universitet, Byggkonstruktion och -produktion, 1990. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18782.
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Holušová, Táňa. "Analýza napjatosti a porušení ve zkušebních tělesech používaných pro určování lomově-mechanických parametrů kvazikřehkých materiálů." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2012. http://www.nusl.cz/ntk/nusl-225575.
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The thesis is focused on a test on determination of the fracture-mechanical parameters of quasi-brittle materials, especially concrete. What is referred to as the wedge-splitting test is considered, for which a variety of shapes of notched specimen can be used. This work is exclusively focused on the cylinder-shaped specimen of diameter 150 mm and breadth of 100 mm. The test is performed virtually using Atena 2D FEM software. Progress of failure is observed during loading of the specimen for various notch lengths. The amount of energy released for the development the failure outside of the tested cross-sectional area (weakened by the notch) is quantified and the size of the fracture process zone is investigated. The described analysis is performed for several material sets witch differ in cohesive properties of the quasi-brittle material expressed via the so-called characteristic length. Suitable proportions of the test specimen are sought, in order to avoid the failure and thus also the energy dissipation outside of the specimen ligament area during the experimental tests, which shall lead to more accurate estimates of fracture-mechanical parameters of the tested material.
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Rintamaa, Rauno. "Single specimen fracture toughness determination procedure using instrumented impact test /." Espoo [Finland] : Technical Research Centre of Finland, 1993. http://bibpurl.oclc.org/web/30658.
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Jernberg, Håkan. "Cleavage fracture toughness at varying specimen size and crack depth." Thesis, KTH, Hållfasthetslära (Avd.), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-258428.
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Cleavage fracture is one of the most severe failure modes in low alloy ferritic steel structures and the fracture toughness is strongly dependent on the size of the specimen, crack depth and temperature. This thesis investigates how the fracture toughness is affected under conditions that relates to size and constraint effects through a fracture mechanical experiment test series. Furthermore, modeling the experiment with a non-local weakest link model to investigate the importance of the stress measure and how the model parameters can be determined for yielding the best result. The experiment is divided into two sets of testing, a pre-test series to determine an appropriate testing temperature for the main test series. The second set consists of four groups with different sizes and crack depth with 12 specimens in each group. The testing temperature was determined to be -155 ◦C. For the large sized test specimen with a shallow crack, the master curve fails to accurately predict the probability of failure by overestimating the fracture toughness. This is not the case for the small test specimens which indicates that the size effects exceeds the low constraint effects for larger sized test specimens and development of the master curve method is needed. When evaluating the stress state in front of the crack tip in the non-local weakest link model, the results yields the least residual error was obtained when using a large sized specimen with high constraint together with a small sized specimen with low constraint for prediction of the probability of failure.
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Gerguri, Shpend. "Brittle fracture criterion for failure prediction of notches and brazed metal-to-ceramic joints." Thesis, Oxford Brookes University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.532050.
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Dobson, Cedric Alan. "Numerical studies of fiber fracture in a single-fiber-composite specimen." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/17636.
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Porr, William C. "Specimen size effects in slow strain-rate testing." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53153.
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A study was conducted to evaluate the effect of specimen dimensions in slow strain-rate environmental effects testing. Tension tests of free machining brass were conducted in a mercuric nitrate solution at a constant crosshead displacement rate of 10⁻³(inch/sec). Thirty-six smooth round bar specimens with different dimensions were tested. It was shown that percent elongation to failure was inversely proportional to an effective ratio of length to diameter, ((D - 2a)L / D²), where D is the specimen diameter, L is the length of the reduced cross section of the specimen, and a is the environmentally induced crack depth. This effective length to diameter ratio correlates with the applied tearing modulus for a cracked round bar tension specimen as defined by P. C. Paris and co-workers in 1979. The results verify that the tearing modulus may be used as a parameter to evaluate tearing instability in terms of elastic-plastic fracture mechanics. More directly, these results show a possible source of error in evaluating the degree of susceptibility to environmentally induced cracking in a material-environment interaction.<br>Master of Science
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Alkilicgil, Cigdem. "Development Of Specimen Geometries For Mode I Fracture Toughness Testing With Disc Type Rock Specimens." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611985/index.pdf.
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Flattened Brazilian disc and modified ring test methods are attractive methods being simpler compared to the other mode I fracture toughness testing methods on rock cores. The aim of this study is to improve these simple methods to yield fracture toughness values that are close to the ones determined by the suggested methods. ABAQUS finite element program was used to determine stress intensity factors of models with various dimensions. Comparing fracture toughness to the results obtained by semicircular bending method tests (0.94 MPa&<br>#8730<br>m for andesite and 0.56 MPa&<br>#8730<br>m for marble) and the cracked chevron notched Brazilian disc method tests (1.45 MPa&<br>#8730<br>m for andesite and 1.08 MPa&<br>#8730<br>m for marble), proper geometrical parameters were investigated by changing diameter, central-hole diameter, and loading angle of Ankara andesite and Afyon marble specimens. Semicircular bending method results were lower than the cracked chevron notched Brazilian disc method results. With flattened Brazilian disc method, the closest results (1.45 MPa&<br>#8730<br>m for andesite and 1.12 MPa&<br>#8730<br>m for marble) to the suggested method was obtained by 54 mm diameter discs with loading angles between 32.5°<br>and 38.0°<br>and with thicknesses between 19 mm and 34 mm. With modified ring test on andesite, the closest results to the suggested method was obtained by 75 mm diameter discs with 8 mm central-hole diameter and 25°<br>loading angle (1.47 MPa&<br>#8730<br>m for andesite and 1.07 MPa&<br>#8730<br>m for marble), and with 14 mm central-hole diameter and 16°<br>loading angle (1.50 MPa&<br>#8730<br>m for andesite and 1.05 MPa&<br>#8730<br>m for marble).
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Chen, Jinwei. "The effects of specimen geometry of susceptibility to stress corrosion cracking (SCC) of steels." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270796.
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Gupta, Kiriti. "Effect of specimen geometry on creep crack growth rate behavior in 1 Cr-1Mo-25V steel." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/20217.
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Dzugan, Jan. "Crack lengths calculation by unloading compliance technique for Charpy size specimens." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-29077.
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The problems with the crack length determination by the unloading compliance method are well known for Charpy size specimens. The final crack lengths calculated for bent specimens do not fulfil ASTM 1820 accuracy requirements. Therefore some investigations have been performed to resolve this problem. In those studies it was considered that measured compliance should be corrected for various factors, but satisfying results were not attained. In the presented work the problem was attacked from the other side, the measured specimen compliance was taken as a correct value and what had to be adjusted was the calculation procedure. On the basis of experimentally obtained compliances of bent specimens and optically measured crack lengths the investigation was carried out. Finally, a calculation procedure enabling accurate crack length calculation up to 5mm of plastic deflection was developed. Applying the new procedure, out of investigated 238 measured crack lengths, more than 80% of the values fulfilled the ASTM 1820 accuracy requirements, while presently used procedure provided only about 30% of valid results. The newly proposed procedure can be also prospectively used in modified form for the specimens of different than Charpy size.
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Dzugan, Jan. "Crack lengths calculation by unloading compliance technique for Charpy size specimens." Forschungszentrum Rossendorf, 2003. https://hzdr.qucosa.de/id/qucosa%3A21733.
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The problems with the crack length determination by the unloading compliance method are well known for Charpy size specimens. The final crack lengths calculated for bent specimens do not fulfil ASTM 1820 accuracy requirements. Therefore some investigations have been performed to resolve this problem. In those studies it was considered that measured compliance should be corrected for various factors, but satisfying results were not attained. In the presented work the problem was attacked from the other side, the measured specimen compliance was taken as a correct value and what had to be adjusted was the calculation procedure. On the basis of experimentally obtained compliances of bent specimens and optically measured crack lengths the investigation was carried out. Finally, a calculation procedure enabling accurate crack length calculation up to 5mm of plastic deflection was developed. Applying the new procedure, out of investigated 238 measured crack lengths, more than 80% of the values fulfilled the ASTM 1820 accuracy requirements, while presently used procedure provided only about 30% of valid results. The newly proposed procedure can be also prospectively used in modified form for the specimens of different than Charpy size.
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Shelke, Jonny M. "Influence of stress state dependency on ductile fracture modeling in standard test specimens using LS-dyna explicit analysis." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439301655.
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Wallace, A. C. "The development of a curved centre cracked specimen for fracture toughness testing of CANDU reactor pressure tubes." Thesis, University of Ottawa (Canada), 1988. http://hdl.handle.net/10393/21626.
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Lin, Sen. "Evaluation of HMA fracture mechanics-based thermal cracking model." Thesis, KTH, Transportvetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-50945.
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Low temperature cracking is an important form of asphalt pavement deterioration in cold regions. The cracks develop when thermally induced stresses exceed the fracture resistance of the asphalt pavement. In this study, by incorporating HMA fracture mechanics into thermal cracking model, a new integrated model is introduced to investigate low temperature cracking performance. To evaluate its reliability and accuracy, the predicted thermally induced stress and failure temperature are compared with the fracture stress and fracture temperature obtained from thermal stress restrained specimen test. The findings indicate that this HMA fracture mechanics-based thermal cracking model has a great potential to reliably evaluate the performance of asphalt mixtures subjected to thermally induced damage.
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Kim, Byung Jun. "Development of small specimen test technique for evaluation of fracture toughness of the structural materials for advanced nuclear systems." Kyoto University, 2011. http://hdl.handle.net/2433/142024.
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Tez, Burkay Yasar. "Effects Of Specimen Height And Loading Span On The Fracture Toughness Of Disc Type Rock Specimens Under Three Point Bending." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609496/index.pdf.
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A relatively new fracture toughness testing method called Straight Notched Disc Bending (SNDB) was used before for fracture testing of Ankara Andesite and Afyon Marble cores. In this work to investigate the applicability of the new method to other rock types. With a preliminary notch of 10 mm, straight notched disc type specimens with a diameter of 75 mm were loaded by three-point bending loads.
Investigation of effect of specimen height on the stress intensity factor and fracture toughness was carried out. Specimen heights (B) between 18 &ndash<br>67 mm were tried for andesite and marble cylindrical specimens. Loading span, that is span/radius (S/R) ratio was changed between 0.6 - 0.9 for andesite specimens.
Stress intensity factor for specimens was computed with ABAQUS program. Stress intensity factor was found to increase with increasing specimen diameter for a fixed span/radius ratio. Stress intensity factor decreased with increasing specimen height.
Changing span was found to have no significant effect on fracture toughness of andesite. Fracture toughness was significantly lower for specimens with smaller height. The suggested testing height interval for this type of specimens was between height/diameter ratios of 0.49 &ndash<br>0.64. Results were compared to the results obtained by a well-known specimen geometry named semi-circular bend specimens (SCB) under three-point bending. SCB tests produced lower values for fracture toughness for both rock types.
Fracture toughness was 0.99 MPa&<br>#8730<br>m for Ankara Andesite and 0.70 MPa&<br>#8730<br>m for Afyon Marble.
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Grasso, Paolo. "Numerical simulations of the effects of residual stresses in adhesively bonded composite specimen." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/10268/.
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In this work the problem of performing a numerical simulation of quasi-static crack propagation within an adhesive layer of a bonded joint under Mode I loading affected by stress field changes due to thermal-chemical shrinkage induced by cure process is addressed. Secondly, a parametric study on fracture critical energy, cohesive strength and Young's modulus is performed. Finally, a particular case of adhesive layer stiffening is simulated in order to verify qualitatively the major effect.
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Campagnolo, Alberto. "Local approaches applied to fracture and fatigue problems." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424240.
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Intentionally designed or accidentally caused, notches, cracks or defects are inevitably present in engineering components and can induce high stress gradients when a far field loading is applied. Then, structural strength assessments are often based on the local stress and strain state in the close neighbourhood of the stress raisers.
The present PhD thesis is divided into six Chapters corresponding to different research topics, all related to new applications of important and widely employed local approaches to notched or cracked structural components.
In the first Chapter, the adopted local approaches, namely the Notch Stress Intensity Factor-based approach (NSIF), the averaged Strain Energy Density (SED) criterion and the Peak Stress Method (PSM), are briefly introduced and described along with their theoretical frameworks.
The second Chapter deals with brittle fracture under mixed mode static loading. A wide experimental campaign has been carried out on PMMA as well as on graphite cracked and notched specimens subjected to mixed mode I+II and I+III loading. Then, all experimental results have been reanalysed by means of the SED approach.
The third Chapter deals with multiaxial fatigue loadings. First, the fatigue strength of severely notched titanium grade 5 alloy, Ti-6Al-4V, has been investigated. Then, the SED criterion has been applied for the first time to an industrial case study, that is the multiaxial fatigue strength assessment of steel welded rollers produced by Rulmeca S.p.a. Finally, some remarks about the phase angle effect on sharp V-notched components under multiaxial fatigue have been drawn on the basis of a proposed analytical frame.
The fourth Chapter addresses the numerical study of 3D effects in notched and cracked components. Initially, the attention has been focused on coupled modes and on the effect of different boundary conditions in 3D cracked discs and plates subjected to nominal mode III or mode II loading. Then, the presence of three-dimensional effects has been investigated both theoretically and numerically in blunt notched components under cyclic plasticity conditions.
The fifth Chapter, instead, is related to the comparison between different fracture criteria. The SED approach and that based on the Finite Fracture Mechanics (FFM) have been compared considering sharp V-notches under pure mode I or mode II loading.
Finally the sixth Chapter address the link between the SED approach and the Peak Stress Method (PSM). Cracks under in-plane mixed mode I+II and out-of-plane mixed mode I+III loading have been investigated. A method to rapidly evaluate the averaged SED based on the peak stresses at the crack tip has been proposed. On the basis of the derived link, some practical applications related to the fatigue strength assessment of aluminium and steel butt welded joints and of tube-to-flange steel welded joints have been carried out.<br>Variazioni geometriche, come intagli, cricche o difetti in generale, sono comunemente presenti nella maggior parte dei componenti meccanici e possono indurre elevati gradienti di tensione per effetto dei carichi esterni. La valutazione della resistenza strutturale dei componenti meccanici è perciò generalmente basata sullo stato di tensione e deformazione locale, nelle adiacenze di tali variazioni geometriche. La presente tesi di dottorato è divisa in sei Capitoli corrispondenti a diversi argomenti di ricerca, tutti relativi a nuove applicazioni di importanti e ampiamente diffusi approcci locali a componenti strutturali intagliati o criccati.
Nel primo Capitolo, sono brevemente introdotti e descritti gli approcci locali adottati, cioè l’approccio basato sul Notch Stress Intensity Factor (NSIF), il criterio basato sulla densità di energia di deformazione mediata (SED) e il Peak Stress Method (PSM), assieme alle loro basi teorico-analitiche.
Il secondo Capitolo si occupa della frattura fragile sotto carichi statici di modo misto. Una campagna sperimentale estesa è stata eseguita su provini intagliati e criccati in PMMA ed in grafite soggetti a carichi di modo misto I+II e I+III. In seguito, tutti i dati sperimentali sono stati rianalizzati per mezzo dell’approccio SED.
Il terzo Capitolo tratta il tema della fatica multiassiale. Inizialmente, è stata investigata la resistenza a fatica di una lega di titanio grado 5, Ti-6Al-4V, severamente intagliata. In seguito, il criterio SED è stato applicato per la prima volta ad un caso studio di interesse industriale: la valutazione della resistenza a fatica multiassiale di rulli saldati in acciaio, prodotti da Rulmeca S.p.a. e caratterizzati da cedimenti alla radice del cordone di saldatura. Infine, prendendo in esame componenti indeboliti da intagli a V acuti soggetti a carichi di fatica multiassiale, sono state tratte alcune osservazioni sull’effetto dell’angolo di fase sulla base di un nuovo approccio analitico.
Il quarto Capitolo tratta lo studio numerico e teorico degli effetti 3D in componenti intagliati e criccati. Inizialmente, l’attenzione è stata focalizzata sui modi accoppiati e sull’effetto di diverse condizioni al contorno in dischi e piastre criccate, tridimensionali e soggette ad un carico nominale di modo III o modo II. Infine la presenza di effetti 3D è stata investigata sia dal punto di vista teorico che numerico in componenti indeboliti da intagli blandi e in condizioni di plasticità ciclica.
Il quinto Capitolo, invece, è relativo al confronto tra diversi criteri di cedimento. Sono stati confrontati l’approccio SED e quello basato sulla teoria della Finite Fracture Mechanics (FFM), considerando intagli a V acuti soggetti a puro modo I o puro modo II.
Infine, nel sesto Capitolo è stato investigato un legame tra il criterio SED ed il Peak Stress Method (PSM). Sono stati presi in esame componenti strutturali criccati soggetti a carichi di modo misto nel piano I+II e fuori piano I+III. È stato proposto un metodo per calcolare rapidamente il SED a partire dalle tensioni di picco valutate all’apice di cricca. Il legame ottenuto tra PSM e SED è stato poi impiegato nella stima della resistenza a fatica di giunti saldati testa a testa in acciaio ed alluminio e di giunti saldati tubo-su-flangia in acciaio sottoposti a carichi torsionali.
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Viehrig, H. W., and D. Kalkhof. "Application of the Master Curve approach to fracture mechanics characterisation of reactor pressure vessel steel." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-61451.
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The paper presents results of a research project founded by the Swiss Federal Nuclear Inspectorate concerning the application of the Master Curve approach in nuclear reactor pressure vessels integrity assessment. The main focus is put on the applicability of pre-cracked 0.4T-SE(B) specimens with short cracks, the verification of transferability of MC reference temperatures T0 from 0.4T thick specimens to larger specimens, ascertaining the influence of the specimen type and the test temperature on T0, investigation of the applicability of specimens with electroerosive notches for the fracture toughness testing, and the quantification of the loading rate and specimen type on T0. The test material is a forged ring of steel 22 NiMoCr 3 7 of the uncommissioned German pressurized water reactor Biblis C.
SE(B) specimens with different overall sizes (specimen thickness B=0.4T, 0.8T, 1.6T, 3T, fatigue pre-cracked to a/W=0.5 and 20% side-grooved) have comparable T0. T0 varies within the 1σ scatter band. The testing of C(T) specimens results in higher T0 compared to SE(B) specimens. It can be stated that except for the lowest test temperature allowed by ASTM E1921-09a, the T0 values evaluated with specimens tested at different test temperatures are consistent. The testing in the temperature range of T0 ± 20 K is recommended because it gave the highest accuracy. Specimens with a/W=0.3 and a/W=0.5 crack length ratios yield comparable T0. The T0 of EDM notched specimens lie 41 K up to 54 K below the T0 of fatigue pre-cracked specimens. A significant influence of the loading rate on the MC T0 was observed. The HSK AN 425 test procedure is a suitable method to evaluate dynamic MC tests. The reference temperature T0 is eligible to define a reference temperature RTTo for the ASME-KIC reference curve as recommended in the ASME Code Case N-629. An additional margin has to be defined for the specific type of transient to be considered in the RPV integrity assessment. This margin also takes into account the level of available information of the RPV to be assessed.
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Islam, Md Shafiqul. "Shear Fracture and Delamination in Packaging Materials : A study of Experimental Methods and Simulation Techniques." Licentiate thesis, Blekinge Institute of Technology, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-13340.
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Packages are the means of preservation, distribution and convenience of use for food, medicine and other consumer products. Package opening is becoming complicated in many cases because of cutting cost in design and production of opening techniques. Introduction of new package opening technique, material or geometry for better opening experience, forces new design measurements which require a large number of prototype developments and physical testing. In order to achieve more rapid and accurate design, Finite Element Method (FEM) Simulations are widely used in packaging industries to compliment and reduce the number of physical testing. The goal of this work is to develop the building blocks towards complete package opening simulation. The study focuses on testing and simulation of shear fracture and shear delamination of packaging materials. A modified shear test specimen was developed and optimized by finite element simulation. Test method was validated for High-density polyethylene (HDPE) and Polypropylene (PP). The developed method has been accepted by international standards organization ASTM. Based on linear elastic fracture mechanics, a geometry correction factor of shear fracture toughness for the proposed specimen was derived. The study concluded that, for ease of opening, HDPE is a more favorable material for screw caps than PP. When performing the experiment with the shear specimen to find essential work of fracture, the ligament length should be varied between twice of the thickness and half of the width of the specimen ligament. Multi-layered thin laminate of Low-density polyethylene (LDPE) and aluminum (Al), also known as Al/LDPE laminate, is another key object addressed in this study. Continuum and fracture testing of individual layers provided the base information and input for numerical modeling. The propagation of an interfacial pre-crack in lamination in Al-LDPE laminate was simulated using several numerical techniques available in the commercial FEM solver ABAQUS, and it was concluded that using the combination of VCCT technique to model the interfacial delamination and coupled elasto-plastic damage constitutive for Al and LDPE substrates can describe interfacial delamination and failure due to necking. It was also concluded that the delamination mode in a pre-crack tip is influenced by the ratio of fracture energy release rate of mode I and II. To address the challenge in quantifying shear energy release rate of laminate with very thin substrate, a convenient test technique is proposed. Additionally, scanning electron microscopic study provided useful information on fractured and delaminated surfaces and provided evidence that strengthened the conclusions of this work. The proposed test methods in this work will be crucial to measure the shear mechanical properties in bulk material and thin substrates. Laminates of Al and LDPE or similar material can be studied using the developed simulation technique which can be effectively used for decision support in early package development.
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Holas, Jiří. "Testování lomové houževnatosti za vysokých teplot s využitím miniaturních CT těles." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231783.
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This master´s thesis deals with the evaluation of fracture behavior of ODS steel MA956 at high temperature range. This behavior was tested by using miniaturized CT specimens, on which were performed experiments to measure of ductile crack growth resistance curves (J-R curves). The value of the fracture toughness was determined from these J-R curves. Fracture properties were consequently evaluated by using fractographic analysis of the fracture surfaces. Structural properties of material was identified by hardness measurement and analyzed by metallographic methods. Results of the measurements show drop of the fracture toughness with respect to the increasing temperature.
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Qadir, Adnan. "Investigation Of Low Temperature Cracking In Asphalt Concrete Pavement." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612696/index.pdf.
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In this study, low temperature cracking of asphalt concrete is investigated based on a laboratory experimental program including the design variables of aggregate type, gradation, asphalt content, binder grading, binder modification, and the experimental variables of cooling rate, and specimen size. The design of experiment is proposed according to the fractional factorial design principles to reduce the required number of test specimens. Mix designs are performed according to the Superpave mix design guidelines using materials obtained from the Turkish General Directorate of High-ways. In the course of this study, a test setup for thermal stress restrained specimen test for asphalt concrete is developed and used successfully to test a number of as-phalt concrete beam specimens. The same setup is also used for measuring the glass transition temperatures to obtain various thermo-volumetric properties of mixtures. Statistical methods are used to identify the effect of experimental variables on frac-ture strength, fracture temperature and other dependent variables obtained from the testing program. Statistical models are also developed to predict the fracture strength, fracture temperature and other thermo-volumetric properties of mixtures. Results of analyses show that aggregate type, binder modification, and asphalt content significantly affect both the fracture strength and fracture temperature of asphalt concrete. While the glass transition temperature is affected by only aggregate type, coefficients of contraction before and after the glass transition temperature are not influenced by any of the experimental variables. The results of this study provide an important basis to prevent low temperature cracking in asphalt concrete pavements.
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Bezerra, Hallyjus Alves Dias. "Estudo da presen?a de entalhes semicirculares em comp?sitos polim?ricos h?bridos." Universidade Federal do Rio Grande do Norte, 2011. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15654.
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Previous issue date: 2011-02-18<br>Composite materials have a wide application in various sectors, such as the medical field in the manufacture of prostheses, in automotive and aerospace. Thus it is essential to the development of new composite and a better understanding in the face of various loading conditions and service. Several structural elements are manufactured in the presence of geometric discontinuity (notch, hole, etc ) in their longitudinal sections and/or cross-cutting, and these affect the mechanical response of these elements. The objective is to study the mechanical response of laminated polymer matrix hybrid composites reinforced with glass fiber/jute in a uniaxial tensile test. The mechanical response takes in account both the influence of the presence of a geometric discontinuity (semicircular notches) and the orientation of fibers in the layers (anisotropy). The semicircular notches are located in longitudinal section (with a reduction in cross section) of the same. In this analysis, the anisotropy is characterized by types of configurations (with different orientations of fibers in the outer layers). A comparative study of mechanical properties with and without the presence of notches is developed. Both configurations consist of four layers of woven jute fiber bidirectional and a central layer of bidirectional woven glass fibers. In addition to the mechanical properties was also studied the characteristics of the fracture developed in each composite laminate. The results showed that in the comparative study, the anisotropy and the presence of semicircular notches directly influences the mechanical behavior of laminates composites, mainly in reducing the tensile strength, and well as the final characteristics of the fracture<br>Os materiais comp?sitos t?m uma ampla aplica??o nos mais variados setores, como por exemplo, na ?rea m?dica na confec??o de pr?teses, na ind?stria automotiva e no setor aeroespacial. Assim ? essencial o desenvolvimento de novos comp?sitos e uma melhor compreens?o frente ?s mais diversas condi??es de carga e servi?o. V?rios elementos estruturais s?o fabricados na presen?a de descontinuidade geom?trica (entalhe, furo etc.) em suas se??es longitudinais e/ou transversais, e essas prejudicam a resposta mec?nica desses elementos. O objetivo do trabalho ? estudar a resposta mec?nica de laminados comp?sitos h?bridos de matriz polim?rica refor?ado com fibras de vidro/juta em um ensaio de tra??o uniaxial. A resposta mec?nica leva em conta tanto a influ?ncia da presen?a de uma descontinuidade geom?trica (entalhes semicirculares) quanto da orienta??o das fibras nas camadas (anisotropia). Os entalhes semicirculares est?o localizados na se??o longitudinal (com redu??o da se??o transversal) dos mesmos. Nessa an?lise, a anisotropia ? caracterizada por dois tipos de configura??es (com diferentes orienta??es das fibras nas camadas externas). Um estudo comparativo das propriedades mec?nicas com e sem a presen?a dos entalhes ? desenvolvido. As duas configura??es consistem de quatro camadas de tecidos bidirecionais de fibras de juta e uma camada central de tecido bidirecional de fibras de vidro. Al?m das propriedades mec?nicas, tamb?m foi estudada as caracter?sticas da fratura desenvolvidas em cada laminado comp?sito. Os resultados mostraram que, no estudo comparativo, a anisotropia e a presen?a dos entalhes semicirculares influi diretamente no comportamento mec?nico dos laminados comp?sitos, principalmente na redu??o da resist?ncia ? tra??o, e bem como na caracter?stica final da fratura
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田中, 啓介, Keisuke TANAKA, 義明 秋庭 та ін. "防振ゴム材料における疲労き裂進展挙動へのJ 積分の適用". 日本機械学会, 2003. http://hdl.handle.net/2237/9154.
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Jelínek, Vladimír. "Lomové chování tepelně ovlivněné oblasti heterogenního svarového spoje." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-230215.
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The study deals with mechanical characteristic of heterogeneous weld joint. The low carbon steel 22K and austenitic steel have been used as a experimetnal materials. The low carbon steel has special properties in basic condition. The sample has been evaluated in basic condition and after annealation. There have been evaluated impact of annealation proces to structure and mechanical charakteristics in experimental part of study. The particularised analysis of microstructure has been done by pictorial analysis. Mechanical characteristics has been examinated in both conditions by 2 different methods – measurment of microhardness according to Vickers and test of fracture toughness on compact tension specimens.
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Marangon, Christian. "Linear and non-linear structural analysis of notched components with local energy approaches." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423490.
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In engineering practice, mechanical components are weakened by a wide range of sharp or blunt notches and their presence has to be accurately taken into account in the design. In fact near notches a strong stress gradient is always induced when a far field loading is applied.
Aiming to investigate the integrity of notched components subjected to different loading histories, for many years to nowadays a lot of stress and strain based damage criteria have been proposed. However, in the last years, some energy based criteria have been introduced and successfully applied on notched members proving to be powerful damage prediction tools.
In particular the averaged strain energy density criterion (Lazzarin and Zambardi 2001) has been developed and used in order to assess the strength of notched components with various notch geometries subjected to different types of loading.
The aim of this work is to extend the validity of the averaged SED criterion to the three-dimensional effects arising in the vicinity of a notch and to the problems induced by the application of multiaxial static and cyclic loadings.
Taking advantage of some results obtained from multiaxial cyclic analyses, the effect of the phase displacement between the applied loads has been addressed presenting a new proposal based on the maximum tangential stress averaged over an entire loading cycle.
Finally, a dedicated software based on the cyclic plasticity theory has been developed in order to obtain the stress/strain distributions at the tip of a rounded notch subjected to uniaxial and multiaxial low cycle fatigue. A particular link between the plastic hysteresis energy at the notch tip and the averaged SED has been found representing the first potential step for a future extension of the averaged SED criterion to cyclic plasticity.<br>Nella pratica ingegneristica, i componenti meccanici sono sovente indeboliti da discontinuità geometriche di diversa forma e dimensione, i quali devono essere tenuti in considerazione in fase di progettazione al fine di evitare malfunzionamenti o collassi strutturali.
Con l’obiettivo di valutare l’integrità strutturale di componenti indeboliti da intagli soggetti a sollecitazioni di diversa natura, numerosi criteri di cedimento sono stati sviluppati considerando lo stato di tensione e/o di deformazione all’apice dell’intaglio o nelle immediate vicinanze di quest’ultimo. Inoltre, negli ultimi anni, sono stati sviluppati approcci di tipo energetico, i quali hanno dimostrato un’ottima attitudine alla previsione del cedimento di componenti intagliati. In particolare, il criterio basato sulla densità di energia di deformazione (SED) mediata all’interno di un volume strutturale è stato presentato da Lazzarin e Zambardi (2001) al fine di valutare la resistenza di componenti intagliati soggetti a diverse sollecitazioni.
L’obiettivo del primo filone di ricerca di questa tesi è quello di estendere e validare il criterio SED considerando sia i modi accoppiati che si generano per effetto Poisson in componenti tridimensionali, sia problemi legati all’applicazione di sollecitazioni di modo misto e di fatica multiassiale.
Prendendo spunto da alcuni risultati ottenuti nel caso di sollecitazioni cicliche, il secondo filone di ricerca ha riguardato lo studio di una proposta in grado di discriminare l’effetto dello sfasamento tra le sollecitazioni su provini intagliati a spigolo vivo soggetti a fatica multiassiale.
Il terzo filone di ricerca ha riguardato l'implementazione di un software in grado di fornire le tensioni e le deformazioni elasto-plastiche all’apice di un intaglio raccordato sottoposto a fatica oligociclica. Infine, è stato possibile trovare un coefficiente di correlazione tra l'area del ciclo di isteresi all'apice dell'intaglio ed il valore della densità di energia di deformazione elasto-plastica all'interno di un volume strutturale.
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Žák, Stanislav. "Pole napětí a deformace v okolí trhlin s komplikovanou geometrií čela zatížených ve smykových zátěžných módech." Doctoral thesis, Vysoké učení technické v Brně. CEITEC VUT, 2018. http://www.nusl.cz/ntk/nusl-390149.
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Tato závěrečná práce je shrnutím výzkumu smykově zatěžovaných trhlin, který proběhl v průběhu čtyř let doktorského studia jejich autora Ing. Stanislava Žáka (Středoevropský technologický institut, Vysoké učení technické v Brně). Předložená práce je zaměřena na prohloubení znalostí v oblasti pokročilé lomové mechaniky, konkrétně pro smykové zatěžování trhlin kombinované s případy geometrických odchylek trhlin od běžně používaných modelů. To mimo jiné znamená návrh nových přístupů a modelů a popis součinitelů intenzity napětí pro geometricky komplikované trhliny. První část práce je věnována shrnutí současných přístupů v lomové mechanice a dále i popisu numerických metod, použitých v dalších výpočtech. Kromě klasických přístupů se tato část textu zabývá i novějším výzkumem zaměřeným na smykové zatěžování trhlin, speciálně pro dva typy zkušebních těles – válcový vzorek s obvodovým vrubem a trhlinou zatížený prostým smykem nebo krutem a CTS těleso umožňující zatížení trhliny v módech I, II a také v jejich kombinaci I+II. Další část textu je zaměřena na konkrétní výpočty lomových parametrů při použití nových modelů s komplikovaným čelem trhliny. Teoretické řešení lomových parametrů pro oba výše zmíněné modely je porovnáno s experimentálními výsledky, získanými v navazujících projektech. U modelu válcového vzorku je popsána možnost zjednodušení budoucích modelů těles s podobným typem komplikované trhliny a současně je na něm popsán lokální vliv zubatosti čela trhliny na indukci lokálního zatížení v módu II při globálním zatížení v módu III. Tyto výsledky jsou přímo propojeny s experimentální kvantifikací únavového šíření lomu při zatížení v módu III. CTS těleso je použito k popisu vlivu drsnosti trhliny na součinitele intenzity napětí. Na tomto modelu je pozorován jak globální pokles hodnoty KII při zvyšující se drsnosti trhliny, tak i lokální změny v namáhání trhliny podél jednotlivých nerovností. Výsledky potvrzují, i pro dosud málo zkoumané smykové zatěžování, že mikrostruktura lomových ploch a čela trhliny má vliv na lomové parametry. Rozšiřují tak současné znalosti v oboru lomové mechaniky popisem geometrického stínění čela trhliny pro zátěžné módy II a III.
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Mrňa, Tomáš. "Vliv velikosti tělesa na R-křivku a na otupení čela trhliny." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-242858.
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The thesis deals with the determination of fracture toughness using compact tension (CT) test specimens at elevated and high temperatures. The experimental material steel P91 designated for application at temperatures 550650°C was used. The fracture toughness in the ductile fracture region of the steel was characterized by the R curve, which characterises the resistance against crack propagation depending on the crack length. The effect of temperature on the R curve at range 23600°C was evaluated. Next the specimen size effect using three sizes of CT specimens at 23°C and the effect of loading rate (2, 0,2 a 0,02 mm/min) at 600°C was examined. The results showed that the temperature has distinct effect on the R-curve, which yields minimal values at 400°C. Only the smallest test specimen size with thickness 6.25mm showed the specimen size effect giving about 10% lower values of toughness comparing to larger specimens. The effect of loading rate was clearly distinguishable. The values of toughness varied about 20% of the toughness value comparing individual loading rate.
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Lokvenc, Martin. "Testování lomové houževnatosti za vysokých teplot s využitím miniaturních CT těles." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231784.
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This thesis deals with a high temperature testing of fracture toughness and studies the size effect on measured values using miniature size CT specimen. Two types of specimen geometry were manufactured from P91 steel, the standard size and the quarter size specimen. J-R curves were obtained in the temperature range from 23°C to 600°C. No specimen size effect was observed at room temperature tests. The realized experiments together with fractography analysis demonstrated the drop of toughness at 400°C caused by the effect of dynamic strain aging.
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Kozáková, Kamila. "Vliv vrubů při cyklickém vysokofrekvenčním únavovém zatěžování." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-443717.
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The diploma thesis deals with the evaluation of the lifetimes of smooth and notched specimens. The comparison of their lifetimes is focused on the case of high-frequency cyclic loading in the area of high-cycle and gigacycle fatigue of materials. The theory of critical distances is used to evaluate and recalculate the life curves of the notched specimens. The effect of the notch is quantified using the Line method. The critical length parameter is determined so that the life curve of the notched specimens corresponds to the curve measured on smooth specimens. The result is the dependence of the critical length parameter on the number of cycles to fracture. Knowledge of critical length parameters can be used to determine the lifetime of notched specimens as well as real notched components using the results of fatigue tests of smooth specimens.
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Vlk, Václav. "Mechanické vlastnosti a lomové chování svarových spojů a základních materiálů přívodního potrubí vodní turbíny." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231314.
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The master thesis is focussed on evaluation of mechanical properties and fracture behaviour of basic materials and weld joints of a water turbine supply pipe. The results of tensile tests, fracture toughness tests, hardness and micro-hardness tests and further chemical and metallography analysis are used for operating degradation level evaluation of the construction material and also for a residual operating recognition of the second, identical specimen of supply pipe.
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Gallo, Pasquale. "Local approaches for the fatigue design of components subjected to high temperature." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424322.
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The present document summarized the aims and the results obtained by the candidate, during the Ph.D. programme. The research activity consisted in the investigation of the high temperature fatigue behaviour, considering the effect of the temperature combined with creep. After a preliminary analysis, the investigation of different notches reproducing the geometry of real components was considered a key topic in the present research activity. These geometries, indeed, are completely neglected in the past and recent literature, despite their important role played in industrial applications. Moreover, the interaction between creep and fatigue is still not well understood and the available design tools are not effective.
Considering a topic so wide and complex, it was essential to approach and face the problems from different viewpoints strictly related one another:
-from the experimental point of view: the aim was the characterization of the high temperature fatigue behavior of different innovative materials, considering a large number of notch geometries, in order to obtain a robust experimental set of new data;
-from analytical/theoretical point of view: with the aim to develop and/or extend methods based on energy approaches to high temperature phenomena, to analyse the elastic-plastic behaviour of the material and try to give robust and reliable tool for the design against creep.
For these reasons, high temperature fatigue tests have been conducted on Cu-Co-Be alloy, 40CrMoV13.9, Titanium grade 2, and a synthesis in terms of the strain energy density of high temperature fatigue data has been proposed successfully, for the first time. In addition, on the 40CrMoV13.9 steel, an investigation on the crack initiation from notches and on the influence of surface roughness at elevated temperature was accurately conducted.
Because of the good results obtained with the SED approach, it was investigated the accuracy of the averaged SED considering a large bulk of high temperature fatigue data taken from literature. Notched components made of different C45 carbon steel at 250°C, Inconel 718 at 500°C and directionally solidified superalloy DZ125 at 850°C were considered. The control volume was derived for each material through the analytical relation within El Haddad-Smith-Topper parameter and the material characteristic length defined by the Theory of Critical Distances. SED based curves were obtained and allowed proving that the proposed approach can be a reliable design tool in practical applications when dealing with high temperature.
Relating to the creep phenomenon, the author developed a useful numerical tool allowing assessing the stress relaxation and the strain evolution against time, at the tip of blunt V-notches. In detail, starting from Neuber’s rule extended to time-dependent problems and assuming Lazzarin-Tovo equations to describe the early elastic state of the system, a set of new differential equations to be solved numerically has been derived in order to predict the evolution of stresses and strains for a material obeying a Norton power law. The results have shown an excellent prediction of the stresses and strains evolution against time, with a maximum discrepancy within theoretical and finite element method prediction of 20%. Some preliminary analyses on the extension of SED under creeping conditions have been also reported.
At the end, the contour J-Integral, developed for elastic-plastic problems, have been also considered for further applications to high temperature and creep.
The results led to several international fruitful collaborations and solid bases for interesting future development of a unified SED approach of fatigue and creep<br>L’obiettivo del Dottorato di Ricerca era lo studio del comportamento a fatica di materiali metallici ad alta temperatura, indagando in modo particolare il fenomeno del creep, che diventa non trascurabile in determinate condizioni di carico e interagisce con la resistenza a fatica stessa. È stata ritenuta interessante soprattutto l’analisi di componenti in presenza di intagli e/o di geometrie complesse che rappresentassero in qualche modo la geometria di componenti effettivamente utilizzati nelle applicazioni industriali.
Da un’iniziale e approfondita analisi bibliografica è emerso come in letteratura si trascurino la fatica ad alta temperatura ad alto numero di cicli e in particolar modo le applicazioni relative a componenti intagliati. Inoltre, l’interazione fra fatica e creep si presenta come un evento ancora poco chiaro e trattato con strumenti poco efficienti.
Considerando fenomeni molto complessi e un tema così ampio, è stato indispensabile affrontare l’oggetto del presente dottorato di ricerca da diversi punti di vista ma strettamente interconnessi:
-quello sperimentale: caratterizzando il comportamento a fatica ad alta temperatura di diversi materiali innovativi e multifunzionali d’interesse industriale, considerando varie geometrie d’intaglio, in modo tale da fornire un consistente numero di dati sperimentali di partenza;
-quello analitico/teorico: cercando di sviluppare e/o estendere approcci energetici ad alta temperatura, analizzando il comportamento elasto-plastico, gli strumenti a disposizione e cercando, infine, di fornire strumenti efficaci per la progettazione in presenza di creep.
Per queste ragioni, è stata condotta una campagna sperimentale al fine di caratterizzare il comportamento a fatica ad alta temperatura di geometrie intagliate di una lega Cu-Co-Be, 40CrMV13.9 a Titanio Grado 2. I dati sperimentali ottenuti sono stati sintetizzati in termini di Strain Energy Density, esteso per la prima volta all’alta temperatura. Sempre considerando l'acciaio 40CrMoV13.9, è stata condotta un’analisi sull’innesco di cricche a bordo foro, ad alta temperatura, valutando l’influenza della rugosità superficiale.
Visti i positivi riscontri ottenuti con la sintesi in energia dei dati sperimentali, la potenzialità del metodo è stata ulteriormente verificata considerando nuovi materiali e geometrie presenti in letteratura. Sono state prese in esame prove a fatica condotte su un acciaio C45 a 250°C, Inconel 718 a 500°C e sulla superlega DZ125 a 850°C. I dati, originariamente sintetizzati attraverso la Teoria delle Distanze Critiche, sono stati ripresentati con successo in termini di densità di energia di deformazione mediata su un volume di controllo. Il raggio di controllo per ogni materiale è stato determinato attraverso la relazione che lega il raggio stesso con il parametro di El Haddad-Smith-Topper e la distanza critica caratteristica del materiale.
Successivamente, il fenomeno del creep è stato accuratamente considerato. In dettaglio, è stato con successo fornito uno strumento numerico capace di prevedere il rilassamento delle tensioni e l’evoluzione delle deformazioni nel tempo, all’apice d’intagli a V raccordati. In dettaglio, partendo dall’estensione della regola di Neuber a problemi dipendenti dal tempo, e utilizzando le equazioni di Lazzarin-Tovo al fine di descrivere lo stato elastico iniziale del problema, è stato poi ricavato un set di equazioni differenziali da risolvere in modo iterativo/numerico al fine di valutare tensioni e deformazioni nel tempo, assumendo la legge di Norton per la rappresentazione del fenomeno del creep. Al fine di validare il metodo, i risultati ottenuti sono stati confrontati con quelli ricavati da accurate analisi agli elementi finiti, ottenendo un buon accordo. Tutte le tensioni sono state previste con errori trascurabili, mentre in alcuni e limitati casi, le deformazioni hanno mostrato un errore percentuale leggermente più elevato ma comunque inferiore al 20%. Sono state inoltre condotte delle analisi preliminari agli elementi finiti al fine di esplorare il comportamento del SED in presenza di creep, risultando tempo-variante ma tendente ad un valore di plateau.
Infine, sono stati considerati approcci energetici alternativi utilizzati nella caratterizzazione dei fenomeni elasto-plastici che possono essere presenti alle alte temperature. In particolare, tra le varie metodologie presenti in letteratura, è stato considerato il J-Integral.
L’attività lascia infine interessanti possibili sviluppi futuri di ricerca che possono portare a un approccio unificato, basato sul SED, per progettazione a fatica in presenza di creep e di forte interazione creep-fatica
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Soret, Clément. "Dimensionnement de canalisations sur des critères en déformation dans des environnements extrêmes." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEM044/document.
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Les standards consacrés à la conception des oléoducs se concentrent principalement sur les chargements opérationnels, tels que les pressions internes et externes, et les procédures d'analyse de défauts actuelles n'exploitent pas les capacités d'écrouissage du matériau. Pourtant, dans des conditions extrêmes, les oléoducs peuvent être soumis à des contraintes au-delà de la limite d'élasticité jusqu'à atteindre 2.5% de déformations plastiques. Ici, les procédures proposées par ExxonMobil et PRCI basées sur des critères en déformation sont présentées, et l'utilisation de l'éprouvette SENT (Single Edge Notched Tension) pour caractériser la ténacité est étudiée, en comparant les différentes procédures d'essais recommandées. Puis, une importante campagne expérimentale a été réalisée pour caractériser deux aciers pour oléoducs à température ambiante et à basses températures. Les comportements mécaniques des matériaux de base et d'apport ont été identifiés grâce à l'utilisation de l'analyse inverse, et il est montré que le modèle d'endommagement GTN permet de modéliser finement les essais sur éprouvettes de laboratoire. Enfin, deux essais sur structures (pression et flexion, puis pression et traction) ont été réalisés de manière à comparer les approches globales et le modèle d'endommagement GTN. Ce dernier démontre une bonne transférabilité de l'éprouvette vers la structure<br>Pipeline design codes and standards traditionally focus on the operational loadings such as internal and external pressures that are likely to exist over the entire lifetime of the pipeline. Existing Engineering Critical Assessments are mostly based on stress considerations, where the design margin is given as a percentage of the yield strength. In extrem environments, pipelines may experience stresses beyond the yield and plastic deformations up to 2.5 %. In such conditions, strain-based design procedures apply. In this work, a literature review of the existing strain based methods is proposed, including ExxonMobil and PRCI multi-tier approaches. The use of the Single Edge Notched Tension (SENT) specimen to measure the material toughness is then studied, benchmarking the recommended testing procedures from literature. A comprehensive experimental campaign was carried out to fully characterize two actual line pipes at room and low temperatures. The mechanical behavior of parent and weld materials are identified using an inverse analysis, and GTN damage model is shown to allow accurate modeling of the laboratory testings. Finally, two full scale tests (pressure + bending or pressure + tension) were carried out to benchmark the global approaches and GTN damage model. The latter showed a very good transferability from specimens to the structure
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Baumgarten, Lars. "Gesteinsmechanische Versuche und petrophysikalische Untersuchungen – Laborergebnisse und numerische Simulationen." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2016. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-202612.
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Dreiaxiale Druckprüfungen können als Einstufenversuche, als Mehrstufenversuche oder als Versuche mit kontinuierlichen Bruchzuständen ausgeführt werden. Bei der Anwendung der Mehrstufentechnik ergeben sich insbesondere Fragestellungen hinsichtlich der richtigen Wahl des Umschaltpunktes und des optimalen Verlaufs des Spannungspfades zwischen den einzelnen Versuchsstufen. Fraglich beim Versuch mit kontinuierlichen Bruchzuständen bleibt, ob im Versuchsverlauf tatsächlich Spannungszustände erfasst werden, welche die Höchstfestigkeit des untersuchten Materials repräsentieren. Die Dissertation greift diese Fragestellungen auf, ermöglicht den Einstieg in die beschriebene Thematik und schafft die Voraussetzungen, die zur Lösung der aufgeführten Problemstellungen notwendig sind. Auf der Grundlage einer umfangreichen Datenbasis gesteinsmechanischer und petrophysikalischer Kennwerte wurde ein numerisches Modell entwickelt, welches das Spannungs-Verformungs-, Festigkeits- und Bruchverhalten eines Sandsteins im direkten Zug- und im einaxialen Druckversuch sowie in dreiaxialen Druckprüfungen zufriedenstellend wiedergibt. Das Festigkeitsverhalten des entwickelten Modells wurde in Mehrstufentests mit unterschiedlichen Spannungspfaden analysiert und mit den entsprechenden Laborbefunden verglichen.
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Sih-YingChen and 陳思螢. "A Study of the Fracture Toughness of API-G Well Cement with Additives Exposed to Supercritical CO2 Environment Using Chevron Notched Brazilian Disc Specimen Test." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/36484254548029241029.
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碩士<br>國立成功大學<br>資源工程學系碩博士班<br>100<br>The carbon dioxide (CO2) deposition in underground geologic sequestration is a feasible approach to reduce CO2 emission. Previous studies have shown that CO2 combines with water to form carbonic acid (H2CO3) which is the formation of an acidic environment of cement erosion. Therefore, the long-term wellbore integrity of the cement sheath should be carefully evaluated to ensure the safe and efficient storage of the CO2.
In this study, the Brazilian notched cement specimens along with other appropriate samples were prepared and were placed into the supercritical carbon dioxide environment over a period of days. The experimental temperature is 70oC and the experimental pressure is 20 MPa. The basic mechanical properties, fracture mechanical properties and chemical structure properties of the API-G well cement with fly ash were investigated. This study finds that the cement specimens have varying degrees of carbonization with the different number of reaction days,. This study also concludes that the API-G cement with fly ash displays the best strength with deepest penetrating depth of carbonization.
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Brown, Niven Rhys. "Application of the double torsion specimen to the study of fracture in fibre reinforced plastics." 1993. http://hdl.handle.net/2292/3323.
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The increasing use of fibre reinforced polymers in structural components often requires an accurate assessment of the strength of the component. The strength of composite materials is usually based on the strength of an individual lamina. This is then combined in a manner depending on the orientation of the plies within the laminate. The actual failure process is often ignored in this type of analysis. Composite failure is the result of damage accumulation from a number of failure modes, in particular, fibre failure, matrix failure and failure of the interface between the fibres and matrix. Measurement of the interfacial strength requires specialised testing techniques in order to obtain accurate characterization of the interfacial failure processes. This research uses a double torsion specimen reinforced with fibres in a number of configurations. The testing techniques developed allow the interaction of a matrix crack with fibres, resulting in the failure of the interface. Finite element analysis has been used to gain an insight into the deformation mechanisms. A compliance change analysis has been developed so that the load in the fibres can be calculated. Results from the finite element analysis confirm the analytical procedures and show that, for the fibre/resin combination tested, the interface has a lower fracture toughness than the matrix material. The interaction between the fibres and matrix shows that the mechanism of fibre bridging inhibits the propagation of matrix cracks. This produces an apparent increase in the toughness of the composite system. To confirm the failure processes occurring, the technique of acoustic emission has been used to monitor the development of the specimen failure. In line with other workers, it is shown that matrix failure produces low amplitude events and interfacial failure produces mid amplitude events. Fibre failure did not occur to any significant degree. This thesis shows how the contribution from the presence of an interface affects the fracture of composite materials and how, via the reinforced double torsion specimen, this contribution can be measured and interpreted.
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Chang, Lin Yi, and 林以常. "The Measurement of Rock Fracture Toughness by the Chevron-Cracked Specimen with Three-Point Bending Test Configuration." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/75622251601832542393.
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碩士<br>國立成功大學<br>資源工程學系<br>88<br>This study intends to measure the fracture toughness of rock materials by the chevron-cracked specimen with three point bending test configuration. The testing devices and arrangements are suggested by The International Society of Rock Mechanics(ISRM, 1988). An LVDT deformation measuring system has been implemented and a special-designed cutting device and supporting fixture system have been developed to measure the Level I fracture toughness of rock materials. The rocks being investigated include sandstone from Nantou, Taiwan and marble from Hualian, Taiwan. The effect of various specifications of the testing specimen is also investigated in this study.
The conclusions of this study are:
1. The average fracture toughness of the sandstone samples being studied is 0.50 MPa∙m1/2, while the average fracture toughness of the marble samples being studied is 1.63 MPa∙m1/2 at foliation angle of 0o and 0.56 MPa∙m1/2 at foliation angle of 90o.
2. The effect of various specifications of the testing specimen used in the sandstone samples can be neglected in this study.
3. Except the effect of specimen length, The effect of the other specifications of the testing specimen used in the marble samples can be neglected in this study. It is observed that decrease in specimen length of marble samples increases the values of maximum loading and fracture toughness.
4. It is observed that increase in foliation angle of marble samples decreases the values of fracture toughness.
5. The formulas, suggested respectively by ISRM and Wu(1984) for calculating the fracture toughness of three point bending test, have shown high compatibility
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Nan-HueiChen and 陳楠輝. "A Study of Measuring the Mode III Fracture Toughness of a Rock Disk Specimen with an Edged Crack." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/08858444148103024818.
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碩士<br>國立成功大學<br>資源工程學系<br>102<br>A loading fixture proposed by Chou (2012) to measure the mode III fracture toughness (KIIIc) of gypsum samples has been adopted in this study. The testing specimens of this study were sandstone rocks which were assumed to be homogeneous and isotropic. The circular rock disks with an edge crack were prepared to be under anti-plane shear loading condition. The mode III fracture toughness test was achieved without confining pressure and was applied by a simplistic loading condition. This study uses the formula suggested by Chen (2009) to compute the values of mode III fracture toughness of the testing rocks.
This study finds that the test proposed by Chou is a reliable method for measuring the mode III fracture toughness of sandstone rocks. The mode III fracture toughness versus temperature is observed in this study. When the temperature is less than 200℃, the mode III fracture toughness gradually increases. When the temperature reaches over 200℃, the mode III fracture toughness is declining. When the temperature reaches over 600℃, no apparent decrease in mode III fracture toughness is observed in the test.
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Baumgarten, Lars. "Gesteinsmechanische Versuche und petrophysikalische Untersuchungen – Laborergebnisse und numerische Simulationen." Doctoral thesis, 2015. https://tubaf.qucosa.de/id/qucosa%3A23031.
Full textAbstract:
Dreiaxiale Druckprüfungen können als Einstufenversuche, als Mehrstufenversuche oder als Versuche mit kontinuierlichen Bruchzuständen ausgeführt werden. Bei der Anwendung der Mehrstufentechnik ergeben sich insbesondere Fragestellungen hinsichtlich der richtigen Wahl des Umschaltpunktes und des optimalen Verlaufs des Spannungspfades zwischen den einzelnen Versuchsstufen. Fraglich beim Versuch mit kontinuierlichen Bruchzuständen bleibt, ob im Versuchsverlauf tatsächlich Spannungszustände erfasst werden, welche die Höchstfestigkeit des untersuchten Materials repräsentieren. Die Dissertation greift diese Fragestellungen auf, ermöglicht den Einstieg in die beschriebene Thematik und schafft die Voraussetzungen, die zur Lösung der aufgeführten Problemstellungen notwendig sind. Auf der Grundlage einer umfangreichen Datenbasis gesteinsmechanischer und petrophysikalischer Kennwerte wurde ein numerisches Modell entwickelt, welches das Spannungs-Verformungs-, Festigkeits- und Bruchverhalten eines Sandsteins im direkten Zug- und im einaxialen Druckversuch sowie in dreiaxialen Druckprüfungen zufriedenstellend wiedergibt. Das Festigkeitsverhalten des entwickelten Modells wurde in Mehrstufentests mit unterschiedlichen Spannungspfaden analysiert und mit den entsprechenden Laborbefunden verglichen.