Dissertations / Theses: 'Diagram of fracture strain'

1

Dubravec, Kristián. "Elastoplastická analýza napětí a deformace a stanovení lomových parametrů při tahovém namáhání těles s koncentrátory napětí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-443729.

Full text

Abstract:

The aim of this thesis is the construction of a diagram of fracture strain for high strength steel OCHN3MFA and its application for the estimation of fracture toughness of this material. The first part of the thesis contains the necessary theoretical framework for numerical modelling of tensile tests of various specimens - smooth specimen, specimen with a notch and specimen with a circumferential crack, it describes the influence of triaxiality on the fracture of bodies and the possibilities of construction of the diagram of fracture strain. Subsequently, a numerical model of these specimens is created using the finite element method (FEM). A non-linear, elastoplastic calculation is performed. Fracture is identified by means of comparing the true stress versus the strain obtained from tests with the finite element analysis results. Stress–strain states of specimens at the moment of fracture are obtained from a numerical model. A diagram of fracture strain is constructed, and it is used to estimate the fracture toughness of a cracked body. Finally, a local approach, which uses the diagram of fracture strain, and a classical approach of fracture mechanics, especially the stress intensity factor, are compared.

APA, Harvard, Vancouver, ISO, and other styles

2

Zhou, Qing 1964. "Analysis of plane strain necking and fracture in strain hardening materials." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/11636.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Mahmood, K. "Influence of strain rate on oxide fracture." Thesis, Cranfield University, 1988. http://dspace.lib.cranfield.ac.uk/handle/1826/11358.

Full text

Abstract:

The ability of metals and alloys to form and retain protective oxide scales is crucial to their stability at elevated temperatures for extended times. Hence the identification of factors that promote or limit the integrity of oxides on high temperature materials has been the subject of intensive investigations. In the present study the mechanical properties of this chromiwm.-rkh scale on 304 stainless steel foil has been investigated in relation to the deformation rates in the substrate. It was shown that heavy cold working (up to 90%) delays the onset of breakaway oxidation and results in a very adherent scale. The cracking behaviour of the scale was found to be strain rate and temperature dependent under slow strain rate conditions when the substrate deforms by creep. No strain rate dependence was observed over the temperature range 700-900°C when faster strain rates (> 10- S sec -1) were applied. The transition between these two responses was found to vary only slightly with temperature between S.Ox10- S sec- 1 and 7.Sx10- S sec -1 ,increasing as the temperature is raised. A new method has been described for determining the fracture behaviour of oxide scale by estimating the composite defect size. From a knowledge of the onset of scale cracking, determined in Sl(U usi ng (h~ acoustic emission technique, it was possible to correlate the measured intercrack spacing with the fracture toughness from which the tensile properties of the scale can be evaluated.

APA, Harvard, Vancouver, ISO, and other styles

4

Alinaghian, Yaser. "The Effect of Pre-strain and Strain Path Changes on Ductile Fracture." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/23917.

Full text

Abstract:

Industrial metal forming operations generally require several deformation steps in order to create the final product. The mechanical behavior of materials undergoing strain path changes can be very different from those deformed in a given direction to fracture. The work presented here employed laser drilled model materials to better understand the effect of pre-strains and strain path changes on void growth and linkage leading to fracture is studied. The experimental results show that increasing pre-strain results in faster void growth which was justified in terms work hardening rate in the sample. Scanning electron microscope images revealed that the ductility of the sample decreased with increasing pre-strain but only slightly compared to the large decrease in far field strain at failure. This suggests that pre-strain affects strain localization significantly and to a lesser extent the ductility. Finally a finite element model has been built to predict the linkage between voids.

APA, Harvard, Vancouver, ISO, and other styles

5

Moore, Andrew J. "Strain analysis using ESPI applied to fracture mechanics." Thesis, Loughborough University, 1993. https://dspace.lboro.ac.uk/2134/11889.

Full text

Abstract:

Electronic speckle pattern interferometry (ESPI) has become an established technique for surface deformation studies. However, difficulties remain in the practical use of ESPI, primarily because results require skilled and time-consuming interpretation. The work reported here has enabled automated acquisition and processing of ESPI displacement data. Further processing has enabled the components of surface strain and stress to be, determined automatically. Such measurements are of great importance for experimental fracture mechanics studies, a quantitative approach to measuring the severity of defects in a loaded structure. Having established the importance of experimental optical methods in fracture mechanics, and the particular advantages of ESPI, a study has been undertaken to determine whether ESPI can be used for quantitative fracture mechanics measurements. Automated analysis for in-plane displacement measurements with ESPI was achieved by the phase-stepping technique. Numerical differentiation of the displacement data allowed surface strain to be evaluated. The accuracy of such measurements was investigated, particularly with regard to speckle noise inherent in the data. Speckle noise limits the accuracy of all measurements, and a practical threshold for displacement and strain of ±0.03~m and ±6~strain was found. From these considerations, two new phase-stepping algorithms have been proposed for ESPI. The first offers improved accuracy by the way it eliminates speckle noise; the second has allowed phase-stepping of ESPI addition fringes for the first time. · In the past ESPI has been restricted to uniaxial measurements. A new interferometer design enabled displacement to be measured along two axes simultaneously: extension to three-dimensional sensitivity is discussed. Automated displacement and strain measurements, recorded with the dual-sensitivity interferometer, are presented for a cantilever loaded at its free end.

APA, Harvard, Vancouver, ISO, and other styles

6

Millereau, Pierre Michel. "Large Strain and Fracture of Multiple Network Elastomers." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066082/document.

Full text

Abstract:

Durant ce travail, nous avons étudié les propriétés mécaniques et de fracture d'élastomères à réseaux multiples synthétisés par des étapes successives de gonflement/polymérisation inspirées de l'architecture moléculaire développée par Gong pour les doubles réseaux hydrogels. Une méthode de synthèse plus versatile a été utilisée pour varier de façon continue le pré-étirement isotrope du premier réseau λ0, qui contrôle le module d'Young et le durcissement. Dans le cas d'une dilution importante du premier réseau (<10%), une scission moléculaire apparaît à grande déformation dans le réseau pré-étiré sans rompre le matériau. Le taux de dilution contrôle la quantité d’endommagement et donc la pente de la courbe contrainte-déformation. Finalement, pour les systèmes les plus dilués (<3%), une striction est observée au-dessus d’un seuil de contrainte. Changer le taux de réticulant du premier réseau ou les monomères utilisés ont conduit par ailleurs à l’obtention de comportements mécaniques similaires. L’énergie de fracture Γ est une fonction croissante de λ0. Des techniques de visualisation locale comme la Corrélation d’Image Numérique et l’intégration de molécules méchanoluminescentes ont été utilisées pour décrire une zone d’endommagement en tête de fissure dont la taille augmente avec λ0. Enfin, le mécanisme de renforcement des élastomères à réseaux multiples a pu être partiellement décrit dans le contexte du modèle de Brown sur les doubles réseaux
We investigated systematically the mechanical and fracture properties of multiple network elastomers synthesized by successive swelling/polymerization steps inspired by the molecular architecture of Gong’s double network gels. A more versatile synthesis method was used to vary continuously the isotropic degree of prestretching λ0 of the first network resulting in a wider range of mechanical behaviours, where λ0 controls the Young’s modulus at small strain and the strain hardening at large strain. If the first network is diluted enough (<10%) molecular bond breakage occurs in this prestretched network at high strain while avoiding sample failure. The degree of dilution controls the amount of damage and therefore the slope of the stress-strain curve. Finally, for the most diluted systems (<3%), a yield stress and a necking phenomenon was observed. Changing the degree of crosslinking of the first network or the monomers used led to the same qualitative mechanical behaviour. The fracture energy Γ was shown to be an increasing function of λ0 however different regimes could be distinguished with macroscopic fracture occurring before or after bulk damage was detected. Visualisation techniques such as Digital Image Correlation and embedded mechanoluminescent molecules were used to map a damage zone in front of the crack tip, the size of which increased with λ0. Finally, the toughening mechanism of the multiple network elastomers could be understood in a nearly quantitative way within the framework of Brown's model of fracture of double network gels

APA, Harvard, Vancouver, ISO, and other styles

7

Fung, Kam-sang. "Fatigue crack propagation with strain energy density approach /." [Hong Kong] : University of Hong Kong, 1989. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12827204.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Martinsen, Vegard. "Micromechanical Modelling of Strain Localization and Fracture in Aluminium." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18812.

Full text

Abstract:

Aluminium is often treated as a homogeneous material. However, when investigated on a microscopic scale, a granular structure is observed. The mechanical properties of the constituents, together with the distribution of stresses and strains, determines the fracture toughness of the material.The objective of this master thesis was to investigate strain localization and fracture in aluminium on a microscopic scale. Relevant literature regarding fracture mechanisms was studied in order to determine which parameters influence the fracture toughness of aluminium. The distribution of effective plastic strain together with the stress triaxiality ratio is thought to give a prediction of the initiation of ductile fracture.A study of the microstructure of aluminium has been carried out. The aim of this study was to gain understanding of the mechanisms leading to the formation of a precipitate free zone (PFZ) near the grain boundary. Also the relation between the mechanical properties of the PFZ and the grain interior was studied. The literature study uncovered that the PFZ is expected to have a low yield stress and a high work hardening rate compared to the grain interior. A simplified numerical model representing a heterogeneous microstructure was developed. The aim of this model was to investigate the effect of certain parameters on the distribution of stresses and strains. The yield stress and work hardening rate of the PFZ as well as the global stress triaxiality, were all variables in a parameter study. A clear tendency of strain concentration in the PFZ was observed, which is consistent with the literature. For low global stress triaxiality, the PFZ oriented at an angle with respect to the external load was found to be the most likely location for initiation of intergranular fracture. Increasing the yield stress and work hardening rate of the PFZ was found to favor transgranular fracture.Due to long computational time, avoiding crystal plasticity analyses is of interest. Whether a material model using isotropic plasticity is able to give the same results as the crystal plasticity model has been investigated. The difference between the average effective plastic strain in the grain interior and in the PFZ was found to be lower using crystal plasticity than when using isotropic plasticity. Using crystal plasticity, the maximum effective plastic strain was found to be dependent of the crystallographic orientations of the grains. However, a more extensive study is required before conclusions regarding the consistency of the results are drawn.

APA, Harvard, Vancouver, ISO, and other styles

9

Dabboussi, Wael. "High strain rate deformation and fracture of engineering materials." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79224.

Full text

Abstract:

Containment structures for aircraft engines must withstand impacts of failed engine components, which may be traveling at extremely high velocities. Therefore, the design of such structures requires a thorough knowledge of material behaviour at high rates of deformation. It is well known that at strain rates above 102 s-1, the yield stress of metals may be significantly different than at quasi-static rates. In addition, material fracture under dynamic loading can also differ from that at slower rates due to manifestation of different failure mechanisms. The purpose of this study was to gain an understanding and determine the constitutive behaviour and failure criteria for several metals used in the aerospace industry; specifically Aluminium (6061-T6), Titanium (Ti-6Al-4V) and Stainless Steel (Nitronic 33). An extensive procedure for determining the constitutive response and ductility limits of those materials, at quasi-static and dynamic strain rates, was developed relying on laboratory experiments and computational simulations. The Johnson-Cook constitutive model coupled with a critical equivalent plastic strain failure criterion was used in simulating the material. Results of the different tests and simulations indicated the success of the modeling process for the 6061-T6 and Ti-6Al-4V, however considerable discrepancies were observed when simulating the behaviour of Nitronic 33 using the Johnson-Cook model. The multiplicative nature of the model, and the high strain hardening of this material were among the reasons the Johnson-Cook is unable to represent the material when simulating events with high strain and high strain rates such as punching.

APA, Harvard, Vancouver, ISO, and other styles

10

Vijayakumar, Vinod. "Stress/strain environments in healing human tibial fractures." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275202.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Wong, Siu-wah. "Predicition of fatigue crack propagation using strain energy density method /." [Hong Kong : University of Hong Kong], 1989. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12751601.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

馮錦生 and Kam-sang Fung. "Fatigue crack propagation with strain energy density approach." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1989. http://hub.hku.hk/bib/B31209713.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

黃小華 and Siu-wah Wong. "Predicition of fatigue crack propagation using strain energy density method." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1989. http://hub.hku.hk/bib/B31209506.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Oess, Ninja P. "Strain measurements using magnetoelastic sensing for wireless bone fracture healing assessment /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17550.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Oduleye, Olusoji Olaleye. "The transport properties of BSCCO superconducting tapes under cyclic stress/strain conditions." Thesis, London South Bank University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267388.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Paul, Graeme William Alexander. "Strain aging of high carbon steel wire." Thesis, University of Strathclyde, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366744.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

MacKenzie, P. M. "Developments in Moire interferometry and its application in experimental fracture mechanics." Thesis, University of Strathclyde, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382405.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Oatway, Wayne Brian. "Time resolved study of the deformation of polyethylene at high strain rates using X-ray diffraction and stress-strain techniques." Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263196.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Guo, Jiulin. "Geometric and spatial heterogeneity in natural fracture systems formed during 3D strain." Thesis, Durham University, 2009. http://etheses.dur.ac.uk/2172/.

Full text

Abstract:

The geometric and spatial heterogeneity in fracture systems of natural fault zones reflect complex strain patterns and exert substantial influences on host rock properties. It has been recognized that general 3D strains will produce diffuse fracture orientation patterns and characteristic kinematics, which are proposed to vary towards the fault core. The bootstrapping methods and spatial correlation analysis [(semi-) variograms] were adopted to investigate the geometric and spatial hetero-geneity in fracture orientations collected systematically with reference to their spatial locations from three distinct fault zones. This relatively rigorous approach revealed that fracture orientation patterns display systematic spatial variations and high spatial correlations traversing fault zones. Factors related to the presence of pre-existing structures and lithologies can modify strains, creating complex fracture patterns and kinematics at different scales and spatial locations. The results suggest that spatially heterogenous fracture networks in subsurface can be highly connected as channels or barriers and will, in anyways, affect the fluid flow path in aquifers.

APA, Harvard, Vancouver, ISO, and other styles

20

Mak, Yew-Poh. "Strain rate effects on tensile fracture and damage tolerance of composite laminates." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/43256.

Full text

Abstract:

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992.
Title as it appears in the June, 1992 MIT Graduate List: Strain rate effects on tensile failure and damage tolerance of composite laminates.
Includes bibliographical references (leaves 133-138).
by Yew-Poh Mak.
M.S.

APA, Harvard, Vancouver, ISO, and other styles

21

Almaari, Firas, and Essam Aljbban. "Strain Rate Effect on Fracture Mechanical Properties of Ferritic-Pearlitic Ductile Iron." Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-78858.

Full text

Abstract:

This study investigates the effect of strain rate on fracture properties of Ferritic-Pearlitic Ductile Iron. A series of dynamic three point bending tests, with various load application rates, are conducted on Charpy V-notch specimens, in room temperature and approximately -18 °C. The tests are performed in a custom-made fixture and during the tests, force and displacement data are recorded. A XFEM (Extended Finite Element Method) model of the test setup has been established and material data from the tests are used as input to the model. The test results show a strong dependency of the strain rate regarding the force needed for crack initiation. Moreover, it can be concluded that low temperature makes the material very brittle, even at low load application rates.

APA, Harvard, Vancouver, ISO, and other styles

22

Al-Quraishi, Ali Abdul Hussain. "The Deformation and Fracture Energy of Natural Rubber Under High Strain Rates." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1185471043.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Alshahrani, Faris. "A Load-to-Fracture and Strain Analysis of Monolithic Zirconia Cantilevered Frameworks." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1468956378.

Full text

APA, Harvard, Vancouver, ISO, and other styles

24

Beaumont, Richard Adrian. "Determining the effect of strain rate on the fracture of sheet steel." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/56768/.

Full text

Abstract:

A key challenge for the automotive industry is to reduce vehicle mass without compromising on crash safety. To achieve this, it is necessary to model local failure in a material rather than design to the overly conservative criteria of total elongation to failure. The current understanding of local fracture is limited to quasi-static loading or strain rates an order of magnitude too high for automotive crash applications. This thesis studies the local fracture properties of DP800 sheet steel at the macroscopic scale from strain rates of to for the first time. Geometries for three stress states, namely plane-strain, shear and uniaxial tension, were developed to determine a fracture locus for DP800 steel using optical strain measurement. These geometries were developed using Finite Element Analysis and validated experimentally for strain rate and stress state. Thermal imaging was used to determine the effect of strain rate on temperature rise and its associated effect on fracture. Fractography was used to examine the specimens’ failure modes at different strain rates. The geometries were applied to the advanced high strength steel grade DP800. Despite prior evidence from simple tensile test data, DP800 showed no significant variation in fracture strain with strain rate in all three stress states. Non-contact thermal measurements showed that the high strain rate tests ( ) were non-isothermal with temperature rises of up to being observed. As a result of this it is difficult to decouple the effect of strain rate from the effect of temperature and requires further investigation. The test geometries were also applied to the deep draw steel DX54 and the aluminium alloy AA5754 where a strain rate effect was observed. Both materials are significantly more ductile than DP800 whish exposed a limitation in the test procedures. At high fracture strains the stress state deviates from its intended value and can invalidate the test. Therefore, a method was developed for determining the validity of a test for each geometry and material from experimental data. The preliminary data from DX54 indicates significantly greater strain rate sensitivity across one order of magnitude than was observed in five orders of magnitude in DP800.

APA, Harvard, Vancouver, ISO, and other styles

25

Noble, Jonathan Paul. "Constitutive relations for materials at high strain rates." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336162.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

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.

Full text

Abstract:

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.
Master of Science

APA, Harvard, Vancouver, ISO, and other styles

27

Lin, Shiann. "Crack analysis by distributed strain nuclei with application to indentation testing." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339286.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Pandya, Kedar Chaitanya. "The study of long term fracture properties in tough polyethylene." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.344082.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Wright, Stuart Charles. "High strain rate response and ballistic impact of polycarbonate." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335252.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Majzoobi, G. H. "Experimental and numerical studies of metal deformation and fracture at high strain rates." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417927.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Cosham, Andrew. "The effect of pre-strain on the fracture toughness of line pipe steel." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614660.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

畔上, 秀幸, Hideyuki Azegami, 五憲權, OHeon Kwon, 勝彦渡辺, and Katsuhiko Watanabe. "き裂エネルギー密度による安定成長き裂の破壊抵抗評価 (第6報, 平面ひずみ形破壊への適用)." 日本機械学会, 1989. http://hdl.handle.net/2237/7261.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Balasundaram, Arunkumar. "Effect of stress state and strain on particle cracking damage evolution in 5086 wrought al-alloy." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/14809.

Full text

APA, Harvard, Vancouver, ISO, and other styles

34

Nava, JoseÌ Manuel Franco. "Finite element versus boundary element analysis of finite strain elastic and elastoplastic fracture mechanics." Thesis, Cranfield University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401612.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Scherer, Jean-Michel. "Strain localization and ductile fracture in single crystals : application to irradiated austenitic stainless steels." Thesis, Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLM026.

Full text

Abstract:

Pour leurs excellentes propriétés mécaniques et d’oxydation, les aciers austénitiques inoxydables sont largement utilisés dans l’industrie nucléaire, en particulier pour les structures internes de coeur des réacteurs. Toutefois, les niveaux d’irradiation neutronique importants auxquels ces matériaux sont exposés peuvent nuire à leurs propriétés mécaniques. Une forte baisse de la ténacité est en effet observée à mesure que la dose d’irradiation augmente. Selon les conditions d’irradiation (température, dose), on distingue principalement deux types de défauts induits par l’irradiation pouvant être responsables de ce comportement : des boucles de dislocations de Frank à basse température d’irradiation (∼300 ◦C) et des nano-cavités à haute température (∼600 ◦C). Comme ces défauts existent et agissent à des échelles inférieures à la taille de grain, leurs effets peuvent être étudiés à l’échelle du monocristal. Tout d’abord, ce travail vise à obtenir des données expérimentales sur le comportement mécanique des monocristaux d’acier inoxydable austénitique. Ensuite, la modélisation de la localisation de la déformation plastique induite par l’adoucissement survenant dans les aciers irradiés est étudiée. Les limites d’un modèle de plasticité cristalline à gradient sont exposées sur la base de prédiction analytiques de l’apparition de bandes de localisation. Une théorie étendue tenant compte de l’évolution de la longueur interne est proposée. Une attention particulière est alors accordée à l’efficacité numérique de la mise en oeuvre par éléments finis du modèle de plasticité à gradient susmentionné. Des formulations basées sur l’approche micromorphe ou sur une approche à multiplicateur de Lagrange sont décrites et comparées à l’aide de simulations par éléments finis. Enfin, un modèle de rupture ductile de monocristaux poreux est proposé – incluant à la fois la croissance et la coalescence des cavités – afin d’étudier l’impact des nano-cavités induites par irradiation sur le comportement mécanique des aciers austénitiques inoxydables. Le modèle est mis en place dans un formalisme à gradient afin de régulariser la rupture ductile
For their excellent mechanical and oxidation properties, austenitic stainless steels are widely used in the nuclear industry, in particular for structural applications inside the core of reactors. However the substantial neutron irradiation levels these materials can be exposed to can detrimentally affect their mechanical properties. A sharp drop of toughness is indeed observed as the irradiation dose increases. Depending on the irradiation conditions (temperature, dose), mainly two kinds of radiation-induced defects can be responsible for this behaviour: dislocation Frank loops at low irradiation temperature (∼300 ◦C) and nano-voids at higher temperature (∼600 ◦C). Since these defects exist and act at the subgrain level, it motivates to study their effects at the single crystal scale. First of all, this work aims at obtaining experimental data on the mechanical behaviour of austenitic stainless steel single crystals. Then, modeling of softening induced strain localization phenomena, as those taking place in irradiated materials, is investigated. The limitations of a reduced strain gradient crystal plasticity model regarding shear bands predictions are exposed on the grounds of analytical solutions and an enhanced theory accounting for internal length evolution is proposed. Thereupon attention is given to the numerical efficiency of the finite element implementation of the aforementionned strain gradient plasticity model. Micromorphic and Lagrange multiplier based formulations of the original theory are described and compared upon finite element simulations. Eventually, one of a kind ductile fracture model of porous single crystals is proposed – including both void growth and void coalescence – in order to investigate impact of radiation-induced nano-voids on the mechanical behavior of irradiated austenitic stainless steels. The model is set up in a strain gradient framework in order to regularize ductile fracture

APA, Harvard, Vancouver, ISO, and other styles

36

Manoharan, Mohan. "Combined mode I - mode III plane strain fracture toughness of two high carbon steels /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487594970651702.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Sutherland, Brandy. "Experimental and analytical analysis of the stress-strain diagram of FRP-confined concrete with different loading rates." Thesis, Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/420.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

Pryce, A. W. "Matrix cracking and stress/strain behaviour of continuous fibre ceramic composite laminates." Thesis, University of Surrey, 1991. http://epubs.surrey.ac.uk/843150/.

Full text

Abstract:

Matrix damage and its effects on mechanical properties have been examined for SiC (Nicalon1) fibre reinforced glass and glass ceramic matrix composites under quasi-static and fatigue loading conditions. Nicalon/Pyrex laminates of different lay-ups have been tested under quasi-static tension. The elastic moduli have been measured and matrix damage monitored as a function of applied strain. The mechanical properties are strongly influenced by the presence of crystalline regions in the matrix which promote microcracking. Laminated plate theory is used to provide bounds to the moduli of the laminates. For unidirectional and simple crossply Nicalon/CAS2 laminates the quasi-static stress/strain behaviour and associated matrix damage accumulation have been examined in detail. The damage development with applied stress was quantified by counts of crack density (in both longitudinal and transverse plies), stiffness loss and cumulative residual strain. The quasi static stress/strain behaviour during continuous tests (accumulating damage) and discontinuous tests (constant damage) have been modelled using a stress analysis based on Aveston, Cooper and Kelly (ACK) theory. The continuous stress/strain behaviour of (0/90) crossply laminates has been modelled using a shear-lag analysis developed previously to describe the transverse ply cracking behaviour of polymer matrix composites. The analysis is modified to account for longitudinal ply cracking. Matrix damage development in unidirectional and (0/90) crossply laminates under quasistatic cycling and high frequency fatigue loading have been studied. For unidirectional laminates stable stress/strain hysteresis loops were obtained during quasi-static cycling, corresponding to stable matrix damage states. These and similar loops obtained after high frequency fatigue are modelled using, the discontinuous stress/strain analysis. It is suggested that the effect of high frequency fatigue is to decrease the interfacial shear strength.

APA, Harvard, Vancouver, ISO, and other styles

39

Falk, Johannes. "Fracture prediction of stretched shear cut edges in sheets made of Dual-Phase steel." Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-13956.

Full text

Abstract:

Dual-Phase (DP) steels, part of the group of Advanced High Strength Steels (AHSS), are used by car manufactures due to its large strength to weight ratio. The high strength of the DP steel does have a negative impact on the formability during sheet metal forming and stretch forming, e.g. fractures often appear in shear cut edges during forming of blanks made of DP steel. The main objective with this thesis is to develop a new punch for Volvo Cars that concentrates the strain to the sheared edges of a test specimen made from different types of DP steel. This is done to be able to measure and obtain maximum fracture strain during stretch forming tests in a press. The newly developed test method is called CTEST (Concentrated Trim Edge Strain Test). The tests are performed with DP steel specimens with three different qualities of the shear cut edges; fine cut, medium cut and worn cut. DP steels tested are DP600GI, DP600UC and DP800GI from three different suppliers. 10 different types of DP steels are tested in this study with different thickness. Thickness of specimens tested are 1 mm, 1.1 mm, 1.5 mm and 2 mm and all specimens tested have a lengthwise (RD) rolling direction. The quality of the sheared cut edge has a great impact to the formability and maximum fracture strain of the specimen. A specimen with a fine cut endures higher fracture strain than medium cut and a worn cut for all types of DP steel with different thickness. A 1 mm thick specimen endures a lower fracture strain than 1.5 mm and 2 mm specimen for all cut qualities. Further, the impact of the orientation of the burr zone of a shear cut edge is studied. With the burr zone facing upwards from the CTEST punch the formability of the specimens is decreased compared to a burr zone facing downwards, especially for a worn cut specimen with micro cracks and imperfections in the edge surface. ARAMIS Digital Image Correlation (DIC) system is used to analyze the specimen edges during press experiments. The ARAMIS results unveil that several small fractures appear in the sheared edges of a specimen just before the specimens split into two pieces. This phenomenon was seen for specimen with worn and medium shear cut qualities. Finite Element (FE) simulations of the CTEST is performed in AutoForm to determine maximum values of the true strain for the three different cut qualities. The simulation in AutoForm does show a slightly higher value of the force and press depth than the value from the press test before maximum fracture strain in reached. The small fractures seen in ARAMIS just before the specimen split into two pieces cannot be seen in the simulation in AutoForm.

APA, Harvard, Vancouver, ISO, and other styles

40

Johnson, David Thomas. "Deformation mechanisms in ABS polymers." Thesis, Cranfield University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341042.

Full text

APA, Harvard, Vancouver, ISO, and other styles

41

Nissley, Nathan Eugene. "Development of the Strain-To-Fracture Test to Study Ductility-Dip Cracking in Austenitic Alloys." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1364214451.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Alsaery, Amani Saleh. "Strain and load-to-fracture comparison of CAD-CAM dental implant crown materials under loading." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483730173077362.

Full text

APA, Harvard, Vancouver, ISO, and other styles

43

Lai, Yeh-Hung. "The constrained blister - a nearly constant strain energy release rate test for adhesives." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/44077.

Full text

Abstract:

This study developed and analyzed a modification of the blister test permitting nearly constant strain energy release rate testing of adhesive bonds. The work consisted of three parts; (1) development of the testing technique to evaluate strain energy release rate and to record the time dependent nature of the fracture process, (2) numerical analysis of the constrained blister test to determine the applicability of an approximate solution for several materials, and (3) development of an. analytical technique to evaluate the strain energy release rate for relatively stiff specimens.

Master of Science

APA, Harvard, Vancouver, ISO, and other styles

44

Horn, Anthony John. "Development of an engineering assessment procedure for predicting cleavage fracture from non-sharp defects using the failure assessment diagram." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515092.

Full text

Abstract:

Current defect assessment procedures assume all flaws to be sharp, a conservative assumption that can lead to pessimistic structural integrity assessment of structures and under-estimation of their safety margin against fracture. This study has developed an engineering assessment procedure for predicting cleavage fracture resistance of structures containing non-sharp defects. The new procedure can be incorporated into existing defect assessment methods via a modification of the Failure Assessment Diagram (FAD). The new procedure was developed and validated using a combination of testing and finite element analysis. A heat-treated structural steel formed the basis for the experimental work. A large test programme of 135 Single Edge Notch Send SEeS) specimens with sharp cracks and U-notches was used to quantify the increase in apparent toughness that occurs with increasing notch root radius p. The Weibull stress-based toughness scaling model was used to predict the increase in cleavage fracture resistance that occurs with increasing p up to a notch radius of 2mm. In the new assessment procedure several new parameters are utilised that are analogous to parameters used in existing constraint correction methods. The notch tip loading severity is described by the elastic notch tip stress ON , analogous to the use of the elastic T-stress used to quantify crack tip constraint in constraint correction. The notch geometry is measured using a loadindependent non-dimensional parameter {3N analogous to the {3r parameter used in constraint correction. Material parameters r and I define the sensitivity of the material toughness to the notch effect; these are analogous to the material parameters a and k used for constraint correction. The parameters r and I can either be obtained from test data or from a series of look-up tables developed using the Wei bull stress-based toughness scaling model. The study also showed that for a given level of constraint defined by the T-stress, the notch and constraint effects are independent of each other. This enables the toughness benefit due to the notch to be applied in conjunction with existing constraint correction methods, e.g. for the assessment of blunt, shallow flaws.

APA, Harvard, Vancouver, ISO, and other styles

45

Nagl, Michael Martin. "Identification of the mechanism of oxide scale fracture, and its correlation with strain using acoustic emission." Thesis, University of South Wales, 1992. https://pure.southwales.ac.uk/en/studentthesis/identification-of-the-mechanism-of-oxide-scale-fracture-and-its-correlation-with-strain-using-acoustic-emission(60f7dec2-bf42-4f44-86f7-b216a1adc662).html.

Full text

Abstract:

Thermally formed oxides scales can protect metals from aggressive environments at high temperatures. However the barrier function is destroyed when the oxide fails. Therefore a new 4-point bend test technique has been developed to measure the failure strains and to study the failure mechanisms of brittle layers in tension and compression. Tests were made with iron oxide and nickel oxide at room temperature and 550 or 900 °C, respectively, using strain rates of 10~* and 10"5 s"1 . Brittle lacquer was used as a model layer. Acoustic emission (AE) was employed to monitor and interpret failure mechanisms together with post test metallography. Equi-distant cracks were formed during failure in tension. Further cracking was affected by elastic and plastic stress relaxation processes, and interface delamination only started after these processes were exhausted. The crack spacing increased with oxide thickness and the results indicated that plastic relaxation processes were dominant at growth temperature conditions. The shear strength of the interface was lower at growth temperature. Shear failure within the layer was found in NiO and brittle lacquer when tested in compression. Failure in iron oxide under compression always started at the interface. The failure mechanism and initiation in compression was determined by the relative shear strength of interface, the shear strength of the layer and the buckling stability of the layer. However, spallation always required crack growth at the interface. Measured failure strains in tension and compression agreed well with the predictions of a model incorporating the fracture mechanics condition for tensile cracking or interface crack growth respectively and factors like residual strains, oxide creep and lateral oxide growth which accounted for the behaviour of a thin growing scale on a thick substrate. The critical fracture mechanics parameter in tension was the composite void size. A K1C value of ~ 1.1 MN nv3/2 was obtained for iron oxide for room temperature and 550 °C. Values of 0.41 and -1.61 MN m3/2 were found for NiO at room temperature and at 900 °C, respectively. The residual growth stresses in iron oxide were determined as approximately zero and the cooling strain from 550 °C was -0.05 - 0.06%. The residual stresses in NiO were -175 MPa at room temperature. The strain energy release rate for interfacial failure in iron oxide was 27 J m-2 and the fracture surface energies were 3.4 and 0.8 J m-2 for iron and nickel oxide, respectively. AE was a useful tool for explaining the failure mechanisms and a numerical analysis showed a slight difference in the AE signal released during tensile and compressive failure.

APA, Harvard, Vancouver, ISO, and other styles

46

McElderry, Susie. "Contrasting deformation styles in the Domeyko Fault System, northern Chile." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366424.

Full text

Abstract:

Subduction of an oceanic plate under the Pacific margin of South America has heen prevalent since Jurassic times. Magmatic and deformation centres have migrated eastward since suhduction began. Northern Chile houses two north-south trench linked strike-slip fault systems, the Atacama Fault Zone and the Domeyko Fault System (DFS). The DFS lies within the Chilean Precordillera from 2 10 to 28°S. Lateral movement began on the DFS in the Eocene. The DFS can be divided into three segments which have apparently undergone differing deformation histories. This study has focused on the central segment of the DFS, to determine fault kinematics and to establish a relative chronology of deformation. Observations have been made in more detail than previous investigations and have heen used to infer the deformation history . Shallow level faulting has resulted in heavily fractured zones with occasional slickenline surfaces. It is difficult to infer kinematics of faulting from these. Much effort has been expended in developing techniques to analyse fracture patterns associated with brittle faulting under conditions of plane strain, simple shear. A novel approach of analysing the shapes of clasts of rock defined by secondary fractures within a fault zone has been used. The clasts approximate ellipses when viewed in 2 dimensions. Combining ellipse orientation and aspect ratio from mutually perpendicular sections through the fault zone allowed calculation of an ellipsoid representative of the clasts of rock in 3 dimensions. Independent determination of the fault kinematics using stratigraphic relationships across the fault, fracture distribution, incremental strain axes and palaeomagnetic analysis has all owed evaluation of the new technique. The shapes of rock clasts are found to be related to the kinematics of the fault system. Up to a critical stage of development of the fault zone the axes of the rock clasts parallel the slip direction, intermediate strain axis and pole to the boundary faults. Which rock clast axis parallels which structural feature depends upon the spacing and curvature of fractures and stage of development of the fault zone. Analysis of the shapcs or rock clasts defined by fractures can avoid bias of the data set towards thicker fractures or against irregular fractures, which can occur when measuring fracture orientations directly. The degree of development of the fault zone varies laterally along the fault over short distances. This causes the shape.: fabric of the rock clasts to change, so predictions of connectivity within a fault zone are limited. The history of the central segment of the DFS determined from this study is found to occur with earlier workers. The complementary deformation histories produced from two scales of ohservation verifies the reliability of the chronology. Lateral movements along the DFS are thought to begin in the Eocene with a sinistral transpressive event which occurred along all three segments of the DFS. En echelon folds, east and west verging thrusts and clockwise rotations associated with sinistral faulting along the master fault of the segment are documented. Later, in the Oligocene, dextral faulting occurred. large clockwise palaeomagnetic rotations, determined from Palaeozoic samples beside the master fault, indicate sinistral displacements have been larger than dextral disp acements. It is inferred that only one episode of large lateral transport occurred. This is the Eocene sinistral event. Normal faulting associated with sinistral displ acements along the western side of the system are documented. This later sinistral faulting has not been documented before in the central segment of the DFS. After Oligocene age dextral faulting, the three segments of the DFS underwent separate deformation histories, as the main Andean deformation foci had moved eastward.

APA, Harvard, Vancouver, ISO, and other styles

47

Prakash, Naveen. "Coupled Electromechanical Peridynamics Modeling of Strain and Damage Sensing in Carbon Nanotube Reinforced Polymer Nanocomposites." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/78803.

Full text

Abstract:

This work explores the computational modeling of electromechanical problems using peridynamics and in particular, its application in studying the potential of carbon nanotube (CNT) reinforced nanocomposites for the purpose of sensing deformation and damage in materials. Peridynamics, a non-local continuum theory which was originally formulated for modeling problems in solid mechanics, has been extended in this research to electromechanical fields and applied to study the electromechanical properties of CNT nanocomposites at multiple length scales. Piezoresistivity is the coupling between the electrical properties of a material and applied mechanical loads, more specifically the change in resistance in response to deformation. This can include both, a geometric effect due to change in dimensions as well as the change in resistivity of the material itself. Nanocomposites referred to in this work are materials which consist of CNTs dispersed in a binding polymer matrix. The origins of the extraordinary piezoresistive properties of nanocomposites lie at the nanoscale where the non-local phenomenon of electron hopping plays a significant role in establishing the properties of the nanocomposite along with CNT network formation and inherent piezoresistivity of CNTs themselves. Electron hopping or tunneling allows for a current to flow between neighboring CNTs even when they are not in contact, provided the energy barrier for electrons to hop is small enough. This phenomenon is highly nonlinear with respect to the intertube distance and is also dependent on other factors such as the potential barrier of the polymer matrix. To investigate this in more detail, peridynamic simulations are first employed to study the piezoresistivity at the CNT bundle scale by considering a nanoscale representative volume element (RVE) of CNTs within polymer matrix, and by explicitly modeling electron hopping effects. This is done by introducing electron hopping bonds and it is shown that the conductivity and the non-local length scale parameter in peridynamics (the horizon) can be derived from a purely physics based model rather than assuming an ad-hoc value. Piezoresistivity can be characterized as a function of the deformation and damage within the material and thereby used as an in-situ indicator of the structural health of the material. As such, a material system for which real time in-situ monitoring may be useful is polymer bonded explosives. While these materials are designed for detonation under conditions of a strong shock, they can be damaged or even ignited under certain low magnitude impact scenarios such as during accidental drop or transportation. Since these materials are a heterogeneous system consisting of explosive grains within a polymer matrix binder, it is proposed that CNTs can be dispersed within the binder medium leading to an inherently piezoresistive hybrid nanocomposite bonded explosive material (NCBX) material which can then be monitored for a continuous assessment of deformation and damage within the material. To explore the potential use of CNT nanocomposites for this novel application, peridynamic simulations are carried out at the microscale level, first under quasistatic conditions and subsequently under dynamic conditions to allow the propagation of elastic waves. Peridynamics equations, which can be discretized to obtain a meshless method are particularly suited to this problem as the explicit modeling of crack initiation and propagation at the microscale is essential to understanding the properties of this material. Moreover, many other parameters such as electrical conductivity of the grain and the properties of the grain-binder interface are studied to understand their effect on the piezoresistive response of the material. For example, it is found that conductivity of the grain plays a major role in the piezoresistive response since it affects the preferential pathways of current density depending on the relative ease of flow through grain vs. binder. The results of this work are promising and are two fold. Peridynamics is found to be an effective method to model such materials, both at the nanoscale and the microscale. It alleviates some of difficulties faced by traditional finite element methods in the modeling of damage in materials and can be extended to coupled fields with relative ease. Secondly, simulations presented in this work show that there is much promise in this novel application of nanocomposites in the field of structural health monitoring of polymer bonded explosives.
Ph. D.

APA, Harvard, Vancouver, ISO, and other styles

48

Gonzalez, Javier Knauss Wolfgang Gustav. "Full field study of strain distribution near the crack tip in the fracture of solid propellants via large strain digital image correlation and optical microscopy /." Diss., Pasadena, Calif. : California Institute of Technology, 1997. http://resolver.caltech.edu/CaltechETD:etd-12212004-164817.

Full text

APA, Harvard, Vancouver, ISO, and other styles

49

Agarwal, Himanshu. "Effect of loading condition, stress state and strain on three-dimensional damage evolution in 6061 wrought Al-alloy." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/14798.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Wallace, Robert James. "Effect of strain rate and bone quality on the bending behaviour of whole bone." Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/9499.

Full text

Abstract:

Forty ovine femurs were harvested and allocated into four testing groups; Fast-Normal, Fast- Decalcified, Slow-Normal, Slow-Decalcified. Contralateral pairings were used within these groups for closer comparison. Dynamic testing apparatus was designed and built allowing rates of strain similar to road traffic accidents to be investigated. These strain rates were achieved by using a pneumatic actuator to apply the load. Slow rate loading was achieved by testing with a commercially available mechanical testing machine at a rate of strain similar to that created by walking. Bone quality was altered by ultrasonically assisted decalcification in EDTA. Levels of mineral dissolution equivalent to the loss of bone mineral density (BMD) of a 75 year old woman were targeted. Whole bone was used for these experiments to facilitate comparison with real fracture radiographs obtained from NHS database. Fracture patterns and degree of comminution were similar between experimental and patient data. Bone is often analysed as a simple beam (engineers bending theory). This method of stress analysis was compared with a method that recognised the change in cross section over the length of the bone. Accounting for this had a highly significant effect on the calculated flexural modulus (p<0.0005).The length to depth ratio of whole bone indicates that shear forces cannot be ignored. The effect of the contribution from shear force on the deflection was investigated. After accounting for deflections due to shear, calculated normal strains agreed with literature values. Deflection due to shear was found to make a significant contribution to the deflection The effect of storage (freezing) on the mechanical properties at high strain rate was evaluated: no significant differences were found for force and deflection at failure. The main body of testing gave the following results: Normal quality bone, rate compared showed significant differences for Ultimate Stress, Ultimate Strain, Yield Strain, Flexural Modulus and Toughness. Demineralising bone resulted in no statistically significant differences between the loading rates for the Stress at failure. Yield Strain, Ultimate Strain, Flexural Modulus and Toughness did show significant differences. The fast loading tests showed significant differences when comparing quality for Stress at failure but not at Yield. Significant differences were found when comparing toughness. Slow loading tests showed significant differences between bone qualities for Stress at failure in contralateral pairs. No significant differences were found for strain or toughness. These results indicate that bone of normal quality can withstand higher than normal stresses for short durations. This ability is lost in demineralised bone. The high loading rate tests revealed closely matched strains at failure for both bone qualities, lending support to the strain based failure theory for bone at traumatic strain rates.

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Diagram of fracture strain'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles