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1
Tossell, D. A. "Mode III fracture mechanics of brittle and semi-brittle materials." Thesis, University of Bristol, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370777.
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Yang, Xiao-Feng. "Aspects of the mechanical behaviour of unidirectional brittle fibre-reinforced brittle matrices." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239805.
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3
Yeung, Conson. "Fracture statistics of brittle materials /." View the Table of Contents & Abstract, 2005. http://sunzi.lib.hku.hk/hkuto/record/B31490323.
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楊光俊 and Conson Yeung. "Fracture statistics of brittle materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B45015211.
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Yaghi, Anas H. "Static and dynamic brittle fracture." Thesis, University of Nottingham, 1993. http://eprints.nottingham.ac.uk/11786/.
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The project examined the static and dynamic fracture mechanics of brittle materials. Destructive testing was performed on brittle, elastic, isotropic and homogeneous epoxy resin specimens made of Araldite CT-200 with Hardener HT-907. Three types of specimen were investigated, namely the three point bend (3PB) beam, the compact mixed-mode (CMM) specimen and the pressure tube. The 3PB and CMM specimens contained both narrow notches and real cracks. The pressure tubes included semi-circular notches. The real cracks were obtained by controlled fatiguing. The research involved the evaluation of the static mode-I and mode-II real and apparent critical stress intensity factors. The fracture surfaces and the phenomenon of crack branching were studied. The dynamic mode-I stress intensity factor was obtained at the inception of crack instability and also at branching. The concept of the existence of a unique relationship between the dynamic stress intensity factor and the instantaneous crack velocity was addressed. The possibility of modelling cracks in structural components by using cast shim notches in epoxy resin was discussed. The modelling of the static behaviour was proposed to be accurate and relatively easy. The dynamic behaviour would be approximately modelled; therefore suggestions on how to improve the dynamic modelling of propagating cracks were recommended, paying particular attention to the branching process and the instantaneous crack velocity. In addition to the experimental work, finite element analysis was conducted for the 3PB and CMM specimens containing narrow notches. It was shown that the specific geometry and loading conditions were unimportant and that the loading was conveniently characterised by the stress intensity factors for an equivalent crack. A method was devised which provided a relatively cheap and efficient means of determining stress concentration factors for what might appear to be complex geometries and loading conditions.
6
Aluko, O. B. "Brittle fracture in soil cutting." Thesis, University of Newcastle Upon Tyne, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383949.
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Parisi, Andrea. "Simulations of brittle dynamic fracture." Thesis, University of Warwick, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397267.
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Howie, Philip Robert. "Measuring plasticity in brittle materials." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610682.
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De, Voy Julian David James. "Failure of creep brittle materials." Thesis, University of Leicester, 1993. http://hdl.handle.net/2381/34757.
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Ts'ai, Hung-ta. "Microcrack toughening in brittle solids /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu148767626101331.
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Hauch, Jens Andreas. "Dynamic fracture in brittle materials /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Kermode, James Richard. "Multiscale hybrid simulation of brittle fracture." Thesis, University of Cambridge, 2008. https://www.repository.cam.ac.uk/handle/1810/253974.
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When a brittle material is loaded to the limit of its strength, it fails by nucleation and propagation of a crack. The conditions for crack propagation are created by the concentration of a long-range stress field at an atomically sharp crack tip, creating a complex and strongly coupled multiscale system. This thesis reports the results of multiscale simulations of the brittle fracture of silicon on the (111) cleavage plane. The simulations are made possible by combining a quantum mechanical description of the processes taking place near the crack tip with a classical atomistic model that captures the long-range elastic relaxation. The 'Learn on The Fly' technique is used to couple the quantum and classical models, allowing accurate quantum forces to be combined with classical forces using a simple adjustable potential to give stable dynamics. The simulations predict that fracture is unstable on the (111) plane at low speeds; conventionally this has been thought of as the most stable crack plane. The instability is caused by a crack tip reconstruction which triggers a positive feedback 'sinking' mechanism leading to macroscopic, experimentally observable corrugations. Recent experiments have observed crack surface features consistent with these predictions. The instability is the first example in a crystalline material of a fracture instability which onsets below a critical velocity, and shows how subtle atomistic details at the crack tip can control the qualitative macroscopic fracture behaviour.
13
Maybee, William Gregory. "Pillar design in hard brittle rocks." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0011/MQ61284.pdf.
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Khouzam, Nelly. "A new class of brittle graphs /." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66048.
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Townsend, D. "Liquid impact properties of brittle materials." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372907.
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Haubensak, Frederick G. (Frederick George). "Microstructure design of porous brittle materials." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/26876.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994.Includes bibliographical references (leaves 214-223).
by Frederick George Haubensak.
Ph.D.
17
Lokas, Rami (Rami Farouk) 1975. "Mechanical behavior of four brittle polymers." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/89284.
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Quintana, Alonso Ignacio. "Fracture mechanics of brittle lattice materials." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611458.
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Yuan, Xiaozhen 1965. "Random initial inhomogeneity in brittle materials." Thesis, The University of Arizona, 1991. http://hdl.handle.net/10150/291367.
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A simplified version of a model that accounts for distributed damage in brittle materials is adopted. It is then extended for the study of the effects of random initial inhomogeneity on material response. A model case regarding random initial inhomogeneity in a structure (specimen) subjected to uniform static compression is studied by including pre-processing and appropriate modifications to a general two dimensional finite element program. From the numerical calculations obtained, the character of damage growth in brittle materials is then studied and discussed.
20
Kullaa, Jyrki. "Constitutive modelling of fibre-reinforced brittle materials /." Espoo : Technical Research Centre of Finland, 1998. http://www.vtt.fi/inf/pdf/publications/1998/P358.pdf.
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21
Morgan, Robert Edward. "Ductile-brittle transitions in pipe grade polyethylene." Thesis, Imperial College London, 1994. http://hdl.handle.net/10044/1/7399.
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Tan, Xin. "Hydro-mechanical coupled behavior of brittle rocks." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2014. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-131492.
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‘Coupled process’ implies that one process affects the initiation and progress of the others and vice versa. The deformation and damage behaviors of rock under loading process change the fluid flow field within it, and lead to altering in permeable characteristics; on the other side inner fluid flow leads to altering in pore pressure and effective stress of rock matrix and flow by influencing stress strain behavior of rock. Therefore, responses of rock to natural or man-made perturbations cannot be predicted with confidence by considering each process independently. As far as hydro-mechanical behavior of rock is concerned, the researchers have always been making efforts to develop the model which can represent the permeable characteristics as well as stress-strain behaviors during the entire damage process.
A brittle low porous granite was chosen as the study object in this thesis, the aim is to establish a corresponding constitutive law including the relation between permeability evolution and mechanical deformation as well as the rock failure behavior under hydro-mechanical coupled conditions based on own hydro-mechanical coupled lab tests. The main research works of this thesis are as follows:
1. The fluid flow and mechanical theoretical models have been reviewed and the theoretical methods to solve hydro-mechanical coupled problems of porous medium such as flow equations, elasto-plastic constitutive law, and Biot coupled control equations have been summarized.
2. A series of laboratory tests have been conducted on the granite from Erzgebirge–Vogtland region within the Saxothuringian segment of Central Europe, including: permeability measurements, ultrasonic wave speed measurements, Brazilian tests, uniaxial and triaxial compression tests. A hydro-mechanical coupled testing system has been designed and used to conduct drained, undrained triaxial compression tests and permeability evolution measurements during complete loading process. A set of physical and mechanical parameters were obtained.
3. Based on analyzing the complete stress-strain curves obtained from triaxial compression tests and Hoek-Brown failure criterion, a modified elemental elasto-plastic constitutive law was developed which can represent strength degradation and volume dilation considering the influence of confining pressure.
4. The mechanism of HM-coupled behavior according to the Biot theory of elastic porous medium is summarized. A trilinear evolution rule for Biot’s coefficient based on the laboratory observations was deduced to eliminate the error in predicting rock strength caused by constant Biot’s coefficient.
5. The permeability evolution of low porous rock during the failure process was described based on literature data and own measurements, a general rule for the permeability evolution was developed for the laboratory scale, a strong linear relation between permeability and volumetrical strain was observed and a linear function was extracted to predict permeability evolution during loading process based on own measurements.
6. By combining modified constitutive law, the trilinear Biot’s coefficient evolution model and the linear relationship between permeability and volumetrical strain, a fully hydro-mechanical coupled numerical simulation scheme was developed and implemented in FLAC3D. A series of numerical simulations of triaxial compression test considering the hydro-mechanical coupling were performed with FLAC3D. And a good agreement was found between the numerical simulation results and the laboratory measurements under 20 MPa confining pressure and 10 MPa fluid pressure, the feasibility of this fully hydro-mechanical coupled model was proven.
23
Bannister, Michael Keith. "Toughening of brittle materials by ductile inclusions." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292024.
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Samuels, J. "The brittle to ductile transition in silicon." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382682.
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Janeiro, Raymond Pinho. "The effect of inclusions in brittle material." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/51621.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009.Includes bibliographical references (p. 137-142).
This thesis experimentally investigates the cracking behavior of brittle heterogeneous materials. Unconfined, uniaxial compression tests are conducted on prismatic gypsum specimens containing either one, or two, inclusions. These inclusions are of different strengths, stiffnesses, shapes, and sizes. Real-time video and high speed video (HSV) systems are used to capture the sequence of cracking events, such as initiation and propagation. The coalescence processes associated with the specimens containing an inclusion pair was also studied. In addition to examining the effects of shape, strength, and stiffness for an inclusion pair, the effect of the inclusion inclination angle on coalescence is also investigated. Some observations reported in this study compare well with those of other researchers, while other observations are quite different. In general, the overall cracking sequences are similar to those reported previously; on the other hand, the amount of debonding observed at the inclusion interface is significantly less. Moreover, the extent of shear crack growth at an inclusion boundary increased substantially in specimens containing two inclusions, compared to those with single inclusions. The coalescence patterns associated with specimens containing an inclusion pair is also compared to past work done by the MIT rock mechanics group on specimens containing double flaws. These results are found to be remarkably similar. In addition to studying cracking behavior, the goal of this study is to provide a database for future work in formulating predictive models on the behavior of materials with inclusions.
by Raymond Pinho Janeiro.
S.M.
26
Heap, M. J. "Creep : time-dependent brittle deformation in rocks." Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/18706/.
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The characterization of time‐dependent brittle rock deformation is fundamental to understanding the long‐term evolution and dynamics of the Earth’s crust. The chemical influence of pore water promotes time‐dependent deformation through stress corrosion cracking that allows rocks to deform at stresses far below their short‐term failure strength. Reported here are results from a study of time‐dependent brittle creep in a suite of sandstones and a basalt under triaxial stress conditions. Results from conventional creep experiments show that creep strain rate is heavily dependent on the applied differential stress, a reduction of only 10% in differential stress results in a decrease in creep strain rate of more than two orders of magnitude. Conventional creep experiments have also demonstrated the possible existence of a critical damage threshold at the onset of the tertiary creep phase. The level of damage in the samples at the onset of acceleration to failure, regardless of the applied differential stress and the creep strain rate, is approximately similar. Furthermore, the relative proportions of the three phases classically used to describe creep are approximately the same, regardless of creep strain rate and rock type. Sample variability results however in significant scattering in the experimental data and numerous experiments are needed to clearly define a relation between the strain rate and the applied stress. Hence, it is demonstrated that stress‐stepping creep experiments provide a means to successfully overcome this problem. The influence of effective stress was investigated in stress‐stepping experiments with effective confining pressures of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the expected purely mechanical influence of an elevated effective pressure results also demonstrate that stress corrosion appears to be inhibited at higher effective pressures. The influence of doubling the pore fluid pressure however, whilst maintaining a constant effective pressure, is shown to have no effect on the rate of stress corrosion. Stress‐stepping creep experiments have also demonstrated that the influence of an elevated temperature (from 20° to 75°C) has a profound effect on stress corrosion. For the same applied constant stress, creep strain rates are seen to increase by up to three orders of magnitude in sandstone. For basalt however, creep strain rates are only modestly affected. This is likely to be due to the high quartz content of sandstone that has been shown previously to be greatly influenced by temperature in double‐torsion experiments. All of the results are discussed in the context of microstructural analysis, acoustic emission hypocentre locations, mineralogy and fits to proposed macroscopic creep laws and a creep flow law. Elastic moduli are crucial parameters for defining relationships between stress and strain. Importantly, volcano monitoring techniques routinely running at Mt. Etna for example, such as seismic tomography and ground deformation modelling, rely on accurate knowledge of elastic moduli. Increasing‐amplitude stress‐cycling experiments have been performed on two extrusive basalts and two porous sandstones. Experiments have shown that stress‐cycling results in a reduction in sample stiffness, equating to a decrease in Young’s modulus and an increase in Poisson’s ratio. These changes are attributed to the growth of new cracks and the extension of pre‐existing cracks during each stress cycle and, hence, an increase in the total crack density. This interpretation is supported by the observation of the Kaiser ‘stress‐memory’ effect, where cracking‐associated microseismicity (acoustic emission or AE) on any stress cycle only occurs when the maximum stress in any previous cycle has been exceeded. It is also shown that in stress cycles in which the previous maximum stress is not exceeded, no AE output is generated and there are no further changes in elastic moduli. The results are interpreted in relation to measurements of tectonic‐volcano (VT) seismicity and deformation at Mt. Etna volcano.
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Wang, Rentong. "Failure mechanism of a brittle layered material." Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1086210643.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xii, 134 p.; also includes graphics. Includes abstract and vita. Advisor: Noriko Katsube, Dept. of Mechanical Engineering. Includes bibliographical references (p. 121-125).
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Venkatachalam, Sivaramakrishnan. "Predictive Modeling for Ductile Machining of Brittle Materials." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19774.
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Brittle materials such as silicon, germanium, glass and ceramics are widely used in semiconductor, optical, micro-electronics and various other fields. Traditionally, grinding, polishing and lapping have been employed to achieve high tolerance in surface texture of silicon wafers in semiconductor applications, lenses for optical instruments etc. The conventional machining processes such as single point turning and milling are not conducive to brittle materials as they produce discontinuous chips owing to brittle failure at the shear plane before any tangible plastic flow occurs. In order to improve surface finish on machined brittle materials, ductile regime machining is being extensively studied lately. The process of machining brittle materials where the material is removed by plastic flow, thus leaving a crack free surface is known as ductile-regime machining. Ductile machining of brittle materials can produce surfaces of very high quality comparable with processes such as polishing, lapping etc. The objective of this project is to develop a comprehensive predictive model for ductile machining of brittle materials. The model would predict the critical undeformed chip thickness required to achieve ductile-regime machining. The input to the model includes tool geometry, workpiece material properties and machining process parameters. The fact that the scale of ductile regime machining is very small leads to a number of factors assuming significance which would otherwise be neglected. The effects of tool edge radius, grain size, grain boundaries, crystal orientation etc. are studied so as to make better predictions of forces and hence the critical undeformed chip thickness. The model is validated using a series of experiments with varying materials and cutting conditions. This research would aid in predicting forces and undeformed chip thickness values for micro-machining brittle materials given their material properties and process conditions. The output could be used to machine brittle materials without fracture and hence preserve their surface texture quality. The need for resorting to experimental trial and error is greatly reduced as the critical parameter, namely undeformed chip thickness, is predicted using this approach. This can in turn pave way for brittle materials to be utilized in a variety of applications.
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Mohseni, Peyman. "Brittle and Ductile Fracture of X80 Arctic Steel." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19487.
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This PhD work has focused on the effect of microstructure and changes in microstructure introduced by welding procedure, on the brittle to ductile transition properties of high strength low alloy steels which have been developed for application at low temperatures (Arctic regions). For this purpose, the experimental work was based on the new pipeline steel API X80 that has a low transition temperature. The relationship between the brittle to ductile transition temperature and the microstructure in the coarse grained heat affected zone, CGHAZ, and the intercritically reheated coarse grained heat affected zone, ICCGHAZ was studied by applying Smitweld TCS1405 weld simulation for producing the HAZ microstructures. During the weld thermal cycles, both single and double cycle, the specimens were resistance heated to 1350°C by a rate of 150°C/s. The cooling rate was adjusted to give a cooling time between 800°C and 500°C (Δt8/5) of 15 seconds. The second heating cycle had a peak temperature, Tp2, of 780°C, and the cooling rate was the same as during the first cycle to simulate the reheated intercritical coarse grained HAZ. Fracture toughness was measured at low temperatures down to -90°C by both tensile and CTOD testing. In order to study the slip system activity of this steel, low cycle three point bending fatigue tests were also performed on polished specimens in the same temperature range. Fracture surfaces and changes in microstructure were analyzed by scanning and transmission electron microscopy and by light optical microscopy. In summary, the present work showed that, at each temperature the ICCGHAZ specimens had lower fracture toughness values than the CGHAZ specimens. Thus, the fracture mechanism is potentially more brittle in the case of ICCGHAZ specimens, and this is probably connected to the microstructure. The microstructure evalutions revealed that the ICCGHAZ contained blocky M-A constituents along prior austenite grain boundaries and stringer M-A constituents between the bainite laths. A more detailed investigation of the fracture surfaces by electron microscopy revealed also the existence of M-A constituents at the initiation points of the cleavage cracks. During deformation, the stress concentration is expected to increase due to the presence of the M-A constituents, and thus the level of stress and strain concentration around the M-A constituents become significantly larger than the nominal stress value and then causes initiation of cleavage fracture. Fracture surface analysis of fractured specimens documented that the cracks initiated either from debonded M-A constituents or from the region between two or more closely separated blocky M-A constituents where the transformation induced stress fields overlapped. In the present work, the initiation of cleavage fracture occurred within the double CTOD distance from the crack tip. This implies that brittle fracture is easily initiated when M-A constituents are located near the fatigue crack tip, and it is also controlled by accumulation of continuum stress fields and local plastic strains. The slip system analysis revealed that several slip systems are activated with a variety of Schmid factors within one grain, and in some cases the first activated slip system is not necessarily that with the highest Schmid factor. Thus, it can be concluded that the Schmid factor is not the only parameter that determines activation of slip. Finally, the crystallographic facet analysis by EBSD illustrated that the {100} planes are the most potent cleavage facet planes in both CGHAZ and ICCGHAZ specimens. It was also shown that the {100} and {110} planes in the case of CGHAZ, and the {100} and {211} planes in the case of ICCGHAZ were the most favourable cleavage facet planes at subzero temperatures.
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Alnaas, Waled. "Nonlinear finite element analysis of quasi-brittle materials." Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/93465/.
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The development of robust solution schemes for the nonlinear finite element analysis of quasi-brittle materials has been a challenging undertaking, due mainly to the stability and convergence difficulties associated with strain-softening materials. The work described in this thesis addresses this issue by proposing a new method for improving the robustness and convergence characteristics of a finite element damage model. In this method, a smooth unloading-reloading function is employed to compute an approximate tangent matrix in an incremental iterative Newton type solution procedure. The new method is named ‘the smooth unloading-reloading’ (SUR) method. A range of examples, based on a set of idealised quasi-brittle specimens, are used to assess the performance of the SUR method. The results from these example analyses show that the proposed approach is numerically robust, effective and results in considerable savings relative to solutions obtained with a reference secant model. Three acceleration approaches are also proposed in this thesis to further improve the convergence properties of the new SUR method. The first acceleration approach, named ‘the predictive-SUR method’, predicts a converged value of a damage evolution variable using an extrapolation in semi-log space. The second proposed method is designated ‘the fixing approach’, in which a damage evolution parameter is updated from the last converged step in Stage-1 iterations and then fixed in Stage-2 iterations. The third acceleration technique employs ‘a slack tolerance’ at key stages in a computation. The improvement of the convergence properties of the SUR method, when the proposed acceleration approaches are introduced, is illustrated using a series of example computations based on the analysis of a range of plain and reinforced concrete structural elements. In addition, a new element with an embedded strong discontinuity is proposed for simulating cracks in quasi-brittle structures. The new formulation is applied to quadrilateral elements and exploited to simulate mode-I, mode-II and mixed mode fracture. The interface element approach and the smeared crack approach are used as reference methods. The results from a series of examples show that the new proposed embedded strong discontinuity approach is both effective and accurate.
31
Nguyen, P. D. "Studies into the Failure Prediction of Brittle Materials." Thesis, Cranfield University, 1987. http://dspace.lib.cranfield.ac.uk/handle/1826/4751.
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This thesis is divided into six chapters. The first chapter
provides a brief introduction concerning the behaviour of brittle
materials. It also contains the justification for the undertaking of
the study as well as a brief description of the method of approach
adopted, and thesis layout. Chapter two provides a critical review of
the current literature available at present in the failure prediction
brittle materials. Both theoretical and experimental studies are
discussed and the relevance to the present work is justified. Chapter three deals with the numerical analyses adopted within
the thesis. Five different failure criteria were utilized in the
initial analysis of the results presented. Among them, the empirical
model using the Principle of Independent Action satisfactorily
represents the biaxial fracture behaviour of brittle materials in
both tension-tension and tension-compression quadrants. Its validity
has never been tested before. Various statistical fracture models
were used to analyze the failure of brittle materials under multiaxial
states of stress, the experimental failure data for simple tension
being a starting point for their calculation. It was shown that the
Energy Density theory led to a better agreement with the experiments
than any other well-known fracture criterion. The study investigates
methods of evaluating the Weibull parameters which were crucial in the
failure prediction of brittle materials. Monte Carlo simulation
techniques are also presented as a method of evaluating the data
ranking for the failure probability of brittle materials. Chapter four is devoted to the description of experimental
techniques adopted in the study, using specially designed rigs. Six
different tests were conducted to evaluate the performance of brittle
materials in static loading and also to enable comparisons with the
theoretical predictions. Attention was given to specimen casting,
loading frames, alignment, measurement techniques and other relevant
parameters. The use of the linear elastic fracture mechanics method
to predict the behaviour of cracks in bodies, which are subjected to
steady stresses, is discussed. The compliance function for the
three-point notch bend specimen is presented in addition to the
determination of the fracture toughness of Herculite LX plaster. The work was also supplemented by the use of scanning electron microscopy
(SEM) to failure analysis of plaster material. This is an extremely
important tool in the study of brittle materials since the dimensions
of small defects and fracture features on individual grains are often
pertinent information to the failure analysis.
Chapter five details the analysis of the theoretical results as
well as the experimental findings. Based upon the previously
mentioned approaches, a comparison was made between theoretically
predicted and experimentally observed data. The comparison indicates
that discrepancies exist between the observed and predicted results,
the reasons for the discrepancies have been justified in this work.
Chapter six provides a brief summary of conclusions derived from
the complete study, together with recommendations for future work.
32
Hall, David Edward. "Analysis of crack growth in creep-brittle materials." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/17118.
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Serbena, F. C. "The brittle-ductile transition of NiAl single crystals." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294341.
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Ellis, M. "The ductile to brittle transition in BCC metals." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306220.
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Ogilvie, D. J. "The genetics of collagen in brittle bone disease." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235046.
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Kent, John. "Probability of brittle fracture for a cracked ship." Thesis, University of Strathclyde, 2007. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21659.
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Fatigue cracking is a common problem in ships and can potentially lead to a catastrophic brittle fracture. This thesis presents a methodology to quantify the risk of leaving these cracks unrepaired while a ship remains in service. The most important variable affecting the probability of failure is the material fracture toughness. Test results carried out on samples taken from a number of ship steel plates are fitted using a modified 'master curve' approach. The approach links fracture mechanics toughness (characterised by Kjc in MPa√m) to the Charpy 27 joule temperature. A major innovation in the work is the use of time-dependent reliability to account for the variation in toughness as the crack extends by fatigue. The loading applied to the crack tip comprises three components: still water bending; wave induced bending; and residual stress. A number of methods used to calculate the probability of failure are compared, with the convolution integral identified as the most suitable. The methodology is successfully benchmarked against the trend in actual failure statistics from the Liberty ships to date. Target probabilities of failure are used to estimate crack lengths for repair. Taking a figure of 5 x 10⁻⁴ events per year as broadly typical of the observed frequency of brittle fracture in merchant ships the methodology suggests that this is equivalent to a crack length of 300 mm in grade A steel at 0°C. Given that cracks are unlikely to be found until they reach 200mm this provides a small margin of safety. For grade D steel the repair length is increased to over 1000mm potentially allowing the repair to be delayed to coincide with scheduled maintenance periods.
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Mühlich, Uwe. "Generalised continuum approach for modelling quasi-brittle failure." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2014. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-137217.
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A proper description of quasi-brittle failure within the frame of continuum Mechanics can only be achieved by models based on so-called generalised continua. This thesis focuses on a strain gradient generalised continuum and provides a specific methodology to derive corresponding models which account for the essential features of quasi-brittle failure. This methodology is discussed by means of four peer-reviewed journal articles. Furthermore, an extensive overview of the state of the art in the field of generalised continua is given at the beginning of the thesis. This overview discusses phenomenological extensions of standard Continuum Mechanics towards generalised continua together with corresponding homogenisation strategies for materials with periodic or random microstructureEine geeignete, kontinuumsmechanische Beschreibung quasi-spröden Versagens ist nur unter Verwendung verallgemeinerter Kontinuumstheorien möglich. In dieser Habilitationsschrift stehen sogenannte Gradientenkontinua im Vordergrund. Für diese wird eine Methodik vorgeschlagen, welche die Herleitung von Modellen erlaubt, die in der Lage sind, quasi-sprödes Versagen adäquat abzubilden. Diese Methodik wird anhand von vier Publikationen dargestellt und diskutiert. Ein umfangreicher Überblick über den Stand der Forschung auf dem Gebiet der veralgemeinerten Kontinuumstheorien wird am Anfang der Habilitationschrift gegeben. Dabei werden neben phänomenologischen Ansätzen zur Ableitung verallgemeinerter Kontinuumstheorien auch die entsprechenden Homogenisierungskonzepte dargestellt. Letztere werden für Materialien mit periodischer Mikrostruktur und für Materialien mit zufälliger Mikrostruktur diskutiert
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Jeng, Fu Shu. "Deep penetration into frictional ductile and brittle materials." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/13096.
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Wood, Joseph D. "Brittle mixed-mode cracks between linear elastic layers." Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/24177.
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Original analytical theories are developed for partitioning mixed-mode fractures on rigid interfaces in laminated orthotropic double cantilever beams (DCBs) based on 2D elasticity by using some novel methods. Note that although the DCB represents a simplified case, it provides a deep understanding and predictive capability for real applications and does not restrict the analysis to a simple class of fracture problems. The developed theories are generally applicable to so-called 1D fracture consisting of opening (mode I) and shearing (mode II) action only with no tearing (mode III) action, for example, straight edge cracks, circular blisters in plates and shells, etc. A salient point of the methods is to first derive one loading condition that causes one pure fracture mode. It is conveniently called the first pure mode. Then, all other pure fracture modes can be determined by using this pure mode and the property of orthogonality between pure mode I modes and pure mode II modes. Finally, these 2D-elasticity-based pure modes are used to partition mixed-mode fractures into contributions from the mode I and mode II fracture modes by considering a mixed-mode fracture as the superposition of pure mode I and mode II fractures. The partition is made in terms of the energy release rate (ERR) or the stress intensity factor (SIF). An analytical partition theory is developed first for a DCB composed of two identical linear elastic layers. The first pure mode is obtained by introducing correction factors into the beam-theory-based mechanical conditions. The property of orthogonality is then used to determine all other pure modes in the absence of through-thickness-shear forces. To accommodate through-thickness shear forces, first two pure through-thickness-shear-force pure modes (one pure mode I and one pure mode II) are discovered by extending a Timoshenko beam partition theory. Partition of mixed-mode fractures under pure through-thickness shear forces is then achieved by using these two pure modes in conjunction with two thickness-ratio-dependent correction factors: (1) a shear correction factor, and (2) a pure-mode-II ERR correction factor. Both correction factors closely follow a normal distribution around a symmetric DCB geometry. The property of orthogonality between all pure mode I and all pure mode II fracture modes is then used to complete the mixed-mode fracture partition theory for a DCB with bending moments, axial forces and through-thickness shear forces. Fracture on bimaterial interfaces is an important consideration in the design and application of composite materials and structures. It has, however, proved an extremely challenging problem for many decades to obtain an analytical solution for the complex SIFs and the crack extension size-dependent ERRs, based on 2D elasticity. Such an analytical solution for a brittle interfacial crack between two dissimilar elastic layers is obtained in two stages. In the first stage the bimaterial DCB is under tip bending moments and axial forces and has a mismatch in Young s modulus; however, the Poisson s ratios of the top and bottom layers are the same. The solution is achieved by developing two types of pure fracture modes and two powerful mathematical techniques. The two types of pure fracture modes are a SIF-type and a load-type. The two mathematical techniques are a shifting technique and an orthogonal pure mode technique. In the second stage, the theory is extended to accommodate a Poisson s ratio mismatch. Equivalent material properties are derived for each layer, namely, an equivalent elastic modulus and an equivalent Poisson s ratio, such that both the total ERR and the bimaterial mismatch coefficient are maintained in an alternative equivalent case. Cases for which no analytical solution for the SIFs and ERRs currently exist can therefore be transformed into cases for which the analytical solution does exist. It is now possible to use a completely analytical 2D-elasticity-based theory to calculate the complex SIFs and crack extension size-dependent ERRs. The original partition theories presented have been validated by comparison with numerical simulations. Excellent agreement has been observed. Moreover, one partition theory is further extended to consider the blister test and the adhesion energy of mono- and multi-layered graphene membranes on a silicon oxide substrate. Use of the partition theory presented in this work allows the correct critical mode I and mode II adhesion energy to be obtained and all the experimentally observed behaviour is explained.
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Navabpour, Payman. "Brittle tectonics and palaeostress reconstructions in the Zagros =." Nice, 2009. http://www.theses.fr/2009NICE4003.
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Cette thèse se concentre sur l’évolution tectonique cassante de la ceinture de plis et chevauchements du Zagros dans les provinces de Fars et Kermanshah de l’Iran. Une reconstruction des pale��o-contraintes liées à l’ancienne marge passive arabe et à sa collision avec la plaque continentale iranienne est proposée. Les structures cassantes complexes, comme attesté par les analyses des rapports géométriques et chronologiques entre des failles, sédimentation tectonique et plis, révèlent de grands changements d’état de contrainte. L’histoire mésozoïque de la marge arable a été caractérisée par le développement de structures en extension héritées du rift au Permo-Trias et de l’ouverture océanique de la Néo-Tethys. L’inversion ultérieure de ces structures pendant la collision a produit une configuration structurale orogénique issue à la fois de la géométrie de marge passive et du processus de fermeture de la Néo-Tethys, caractérisée par une obduction ophiolitique discontinue et une collision continentale diachrone. La collision continentale du Cenozoïque moyen et tardif est caractérisée par des structures compressives et des décrochements révélant une réorientation des contraintes. Cette réorientation des contraintes, cohérente avec un changement graduel de la cinématique des plaques dans le Fars, ne coïncide pas avec le changement cinématique à Kermanshah, où se produit un partitionnement de la déformation à l’échelle orogénique avec une convergence oblique des plaques. Le changement des contraintes a été plus probablement résulté de la dernière réorganisation de la collision, caractérisée par une augmentation du couplage des plaquesThis dissertation focuses on brittle tectonic evolution of the inner zones of the Zagros fold-and-thrust belt in the Fars and Kermanshah provinces of Iran. A palaeostress reconstruction of the former Arabian passive margin and its collision with the Iranian continental plate is carried out. Complex brittle structures, as evidenced by field-based analyses on geometric and chronologic relationships between faults, syn-tectonic sediments and folds, reveal major changes in stress regimes. The Mesozoic history of Arabian margin was characterised by extensional structures inherited from the Permina-Triasic rifting and the Neo-Tethyan oceanic opening? During the continental collision, subsequent inversion of these inherited structures resulted in an orogenic structural pattern, which helped reconstructing not only the geometry of passive margin but also the Neo-Tethyan closure process, as characterised by discontinuous ophiolite obduction and diachronous continental collision. The mid-late Cenozoic continental collision is characterised by compressional and strike-slip structures, revealing stress reorientation? This stress reorientation has been fairly consistent with a gradual change in plate kinematics in Fars, but not chronogically consistent with the plate kinematic in Kermanshah, where orogenic-scale deformation partitioning occurs under an oblique plate convergence. The change in stress state has more likely been related to the late collisional plate reorganisation, as highlighted by an increase in coupling between the plates
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Nguyen, Thang Dinh. "Theoretical study of thermal spalling of brittle materials." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/77905.
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In this work several problems related to thermal spalling are considered. First, a novel approximate technique to solve general linear heat-conduction problems with changing boundary conditions and locations is proposed. The technique is based on the concept of linear superposition and the possibility to transform the initial condition into a time-varying boundary condition. The proposed technique is evaluated and compared_to some of the existing techniques. The individual contribution of several stress components and their combined effects on the risk of failure are then considered for a theoretical axi-symmetric body subjected to uniform unconfined heating. The results indicate that using a single stress component in the prediction of failure for brittle materials is not justified in general. Finally, the thermal spalling process in jet piercing operations is studied. The finite element model consists of a large axi-symmetric object subjected to a confined heat flux. The numerical results are used to study the combined effects of several stress components and the influence of material properties and heat flux intensity on the spalling rate and spallability of brittle materials. The results compare favorably with experimental results reported in the literature. A set of plots are offered for use in design. Possible extensions and variations of the present work are also discussed.Ph. D.
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Zhao, Yue. "How Plasticizer Makes a Ductile Polymer Glass Brittle?" University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1460160287.
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Lu, Yue. "Polystyrene Glasses Under Compression: Ductile and Brittle Responses." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1523271245493476.
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Narayan, Sooraj. "A gradient-damage theory for quasi brittle fracture." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122236.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 73-77).
Phase-field modeling of brittle fracture of linear elastic solids has been the subject of several studies in the past 25 years. An attractive feature of this approach to model fracture is its seamless ability to simulate the complicated fracture processes of nucleation, propagation, branching and merging of cracks in arbitrary geometries. While most existing models have focussed on fracture of "ideal brittle" materials, we consider fracture of "quasi-brittle" materials. The material is considered to be quasi-brittle in the sense that it does not lose its entire load-carrying capacity at the onset of damage. Instead there is a gradual degradation of the strength of the material, which is the result of microscale decohesion/damage micromechanisms. In this thesis we discuss the formulation of our gradient-damage theory for quasi-brittle fracture using the virtual-power method. The macro- and microforce balances, obtained from the virtual power approach, together with a standard free-energy imbalance law under isothermal conditions, when supplemented with a set of thermodynamically-consistent constitutive equations will provide the governing equations for our theory. We have specialized our general theory to formulate a simple continuum model for fracture of concrete - a quasi-brittle material of vast importance. We have numerically implemented our theory in a finite element program, and simulated numerical examples which show the ability of the simulation capability to reproduce the macroscopic characteristics of the failure of concrete in several technically relevant geometries reported in the literature..
by Sooraj Narayan.
S.M.
S.M. Massachusetts Institute of Technology, Department of Mechanical Engineering
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Yerro, Colom Alba. "MPM modelling of landslides in brittle and unsaturated soils." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/401186.
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Landslides and slope instabilities represent one of the most important problems in geotechnics causing significant damages around the world every year. Understanding the mechanics of the whole process is of particular importance for risk assessment. First, it is important to determine what areas may be susceptible to landsliding. In addition, it is essential to estimate the travelled distance and the velocity of the unstable mass in order to prevent severe damage. The need to develop solution schemes capable of simulating failure initiation as well as post-failure dynamics is also required in most geotechnical analyses. For instance the design of dams, tunnels, pipes, foundations or embankments.
The prediction of such catastrophic episodes presents several challenges due to the complexities of real soil behaviour. In addition, the consideration of the coupled behaviour of soil and pore fluids is essential by means coupled hydromechanical formulations. Traditional geotechnical analysis, such as Limit Equilibrium Methods (LEM), and the well-known standard lagrangian Finite Element Methods (FEM) are very useful to study the failure initiation, but they provide limited information on the post-failure behaviour. In order to overcome such difficulties, modern numerical approaches are being developed. This is the case of the Material Point Method (MPM), which offers an interesting alternative. MPM discretises the media into a set of lagrangian material points which move attached to the material carrying the soil properties. Governing equations are solved incrementally at the nodes of a computational grid that remains fixed through the calculation. This dual description of the media prevents mesh distortion problems.
This Thesis focusses on studying brittle failures and slope instabilities, from static conditions to run-out. Relevant aspects for the interpretation of landslides are described: the development of progressive failure mechanism, the role played by internal shearing in compound slides, and the effect of brittleness on the onset of failure and run-out.
Different slope instabilities are presented. First, the Selborne slope experiment is simulated. This case, well identified with laboratory data, has been an opportunity to perform a validation of the MPM formulation. A simplified geometry of the Vajont landslide is also analysed in a second modelling. It has shown that a kinematically admissible failure mechanism requires internal shearing of the mobilised mass controlled by the geometry of the basal sliding surface. In addition, by means of a parametric study varying peak and residual strength, run-out is found to be directly related with brittleness index.
Finally, a step forward in the application of MPM to multi-phase problems in porous media has been achieved. In order to simulate the behaviour of unsaturated materials, MPM has been extended by means a coupled 3-phase 1-point MPM formulation. In this way, the interaction of three different phases (solid liquid and gas) is taken into account within each material point. This approach is validated by means the modelling of an infiltration problem. Finally, an embankment slope instability induced by heavy rain has been simulated.
Two constitutive models are used in the applications: a brittle model with strain softening for saturated soils, and a Mohr-Coulomb elastoplastic model formulated in terms of net stress and suction.Les esllavissades representen un dels problemes més destacats en el camp de la geotècnia ja que cada any causen danys importants arreu. La comprensió de la mecànica de tot el procés és de particular importància en l'avaluació de riscos. En primer lloc, és important determinar quines zones poden ser susceptibles a lliscaments o inestabilitats. A més a més, també és essencial estimar la velocitat i la distància recorreguda per la massa inestable. El desenvolupament de tècniques numèriques capaces de simular de forma unificada des de l'inici de la trencada fins a l'estabilització final són claus en problemes d'estabilitat de talussos però també en altres anàlisis geotècnics. Per exemple, en el disseny de preses, túnels, canonades, fonamentacions o terraplens. La predicció d'aquest tipus d'episodis catastròfics presenta diversos reptes a causa de la complexitat del comportament real del sòl. A més, la implementació de formulacions hidro-mecàniques és vital per tal de tenir en compte l'efecte de fluids (líquid i/o gas) dins la matriu porosa del sòl. Els anàlisis geotècnics tradicionals, com ara els mètodes d'equilibri límit (MEL) i la formulació clàssica del mètode dels elements finits (MEF) són molt útils per estudiar l'inici de la trencada, però proporcionen informació molt limitada de la posttrencada i del comportament de la massa mobilitzada. Actualment, s'estan desenvolupant mètodes numèrics capaços de simular de forma unificada tot el procés (trencada i posttrencada), com per exemple el Mètode del Punt Material (MPM) que ofereix una alternativa interessant. El MPM discretitza el medi continu mitjançant un conjunt de punts lagrangians que es mouen units al material (punts materials) i transporten les propietats d'aquest. Per altra banda, les equacions de govern es resolen de forma incremental als nodes d'una malla computacional que roman fix durant tot el càlcul. Aquesta doble discretització evita els problemes de distorsió de malla típics en el MEF. Aquesta tesi es centra en la simulació d'esllavissades i inestabilitats de talussos, analitzant les condicions estàtiques inicials, la formació de la trencada i el comportament post-trencada. Es descriuen diferents aspectes rellevants per a la interpretació de les esllavissades: el mecanisme de trencada progressiva, el paper exercit per la degradació interna del material i l'efecte de la fragilitat del material en la trencada i en el desplaçament final. Es presenten diferents casos. En primer lloc, es simula l'experiment de Selborne. Aquest cas, ben identificat mitjançant dades de laboratori, ha estat una oportunitat per dur a terme una validació de la formulació MPM. Una geometria simplificada de l'esllavissada de Vajont també s'analitza en un segon model. S'ha demostrat que un mecanisme de trencada cinemàticament admissible requereix el cisallament i la degradació interna de la massa mobilitzada depenent de la geometria de la superfície basal de lliscament. A més, per mitjà d'un estudi paramètric variant les resistències pic i residual, s'ha determinat que l'abast està directament relacionat amb la fragilitat del material. Finalment, s'ha aconseguit fer un pas endavant en l'aplicació del MPM en problemes multi-fàsics en medis porosos. Per tal de simular el comportament del sòls no saturats, la formulació MPM s'ha ampliat mitjançant una formulació MPM acoblada amb 3 fases. D'aquesta manera, es té en compte la interacció de sòlid, líquid i gas en cada punt material. Aquest enfocament s'ha validat mitjançant un problema d'infiltració. Finalment, es presenta la inestabilitat d¿un terraplè, en terreny no saturat, degut a fortes pluges. En les diferents aplicacions presentades, s'utilitzen dos models constitutius: un model fràgil amb reblaniment per sòls saturats, i un model elastoplàstic de Mohr-Coulomb formulat en tensió neta i succió.
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Cardoso, Nungaray Víctor Eduardo. "Discrete volume method : a variational approach for brittle fracture." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/565906.
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This thesis presents a proposal to simulate mechanics and dynamics of brittle fracture. A variational formulation is used to describe Lagrangian mechanics, by minimizing the difference between potential and kinetic energy of the system, obtaining a pair of partial differential equations; the solution of these equations corresponds to the displacement field and damage phase-field respectively. Such an equations are coupled in the sense that the damage field is used in the first equation and the displacement field is used in the second one.
In this work we propose a numerical method based on control volumes to solve the differential equations, extending the formulation to support the separation of control volumes, processing these volumes as discrete entities. This treatment results in accurate calculations of stress field and the nucleation of new internal fractures that can be propagated through domain creating multiple bifurcations.
To integrate equations inside control volumes we introduce a family of polynomial splines that we refer as homeostatic splines, since its derivatives are null at vertices with a smooth function variation between adjacent volumes. Furthermore, we propose a shape function with trigonometric components for dynamic analysis, allowing bigger time steps that with traditional approaches.
Finally, we perform ten numerical experiments to show the effectiveness of the method and to compare our results with those published by other authors.La tesis presenta una propuesta para simular la mecánica y dinámica del fenómeno de fractura frágil. Se plantea una formulación variacional que consiste en minimizar la diferencia entre la energía potencial y la energía cinética del sistema, obteniendo así un par de ecuaciones diferenciales parciales, cuya solución corresponden al campo de desplazamientos y al campo de daño respectivamente. Estas ecuaciones están acopladas en el sentido de que el campo de daño se usa en la primera ecuación y el de desplazamientos en la segunda. En este trabajo se propone un método numérico basado en volúmenes de control para resolver las ecuaciones diferenciales, además el modelo se extiende para soportar la separación de los volúmenes de control, tratándolos posteriormente como entidades discretas, esto permite calcular con precisión el campo de esfuerzos y la aparición de fracturas internas que pueden propagarse a través del dominio y crear múltiples bifurcaciones. Para integrar las ecuaciones dentro de los volúmenes de control se introducen una familia de splines polinomiales, que se les refiere como splines homeostáticos, ya que sus derivadas son nulas en los vértices y el cambio de la función entre dos volúmenes contiguos es suave. Además, se propone una función de forma con componentes trigonométricas para el análisis dinámico, permitiendo pasos de tiempo más grandes que con enfoques tradicionales. Finalmente se realizan diez experimentos numéricos para mostrar la eficacia del método y contrastar los resultados con aquéllos publicados por otros autores.
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Presiado, Rhea Suzanne. "Biogeography of the brittle star Ophioplocus esmarki (Echinodermata: Ophiuroidea) /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
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Zeitlhöfler, Matthias. "Brittle Petrofabrics in the Central Bavarian Forest (SE Germany)." Diss., lmu, 2007. http://nbn-resolving.de/urn:nbn:de:bvb:19-78457.
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Rolo, Reinaldo. "The anisotropic stress-strain-strength behaviour of brittle sediments." Thesis, Imperial College London, 2004. http://hdl.handle.net/10044/1/8239.
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Greenshields, Christopher John. "Fast brittle fracture of water/air pressurised plastic pipes." Thesis, Imperial College London, 1995. http://hdl.handle.net/10044/1/8690.
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