Dissertations / Theses on the topic 'Rupture criterion'
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Barthélémy, Jean-François. "Approche micromécanique de la rupture et de la fissuration dans les géomatériaux." Marne-la-vallée, ENPC, 2005. https://pastel.archives-ouvertes.fr/pastel-00001296.
Michaut, Vincent. "Modélisation de la fragmentation dynamique par la méthode des éléments discrets." Phd thesis, Ecole Centrale Paris, 2011. http://tel.archives-ouvertes.fr/tel-00601766.
Bui, Thanh Quang. "Caractérisation de l'amorçage de fissure dans les assemblages collés : application à l'adhérence moléculaire renforcée." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4729/document.
Direct bonding by molecular adhesion is a bonding technique based on joining two surfaces into direct contact without the use of any adhesives or additional material. Such an operation requires the surfaces that are to be bonded to be sufficiently smooth and for them to be sufficiently close together to allow contact to be initiated. Mechanical characterization of this type of assembly with classical mechanical test as for instance wedge test, cleavage test or double shear test present a highly defects sensitivity on mechanical results.The first objective of this work concerns the design and the development of a new test for the analysis of crack initiation in order to obtain results less dispersed than conventional tests particularly for fragile adhesives with small thickness as molecular bonding. Only the mode I was investigated and an experimental device based on modified DBC classical test is proposed to study crack initiation with different edge geometries (homogeneous, high stress concentration).The second objective proposed, in starting from the different experimental results obtained, to compare some approaches (PSC, CC, MZC) to predict crack initiation for fragile adhesives and in particular for molecular bonding. The idea is to propose a simple methodology for engineers in order to predict fracture in an assembly bonded with an adhesive thickness close to zero
Brunel, Jean-Evrard. "Influence de l'endommagement sur la rupture de plaques composites en présence de surcontraintes." Paris 13, 1989. http://www.theses.fr/1989PA132008.
Reck, Bernhard. "Comportement mécanique anisotrope des composites stratifiés carbone/époxyde sous contraintes complexes : élasticité, endommagement, rupture." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10183.
Raviol, Jolan. "Vers l'évaluation du risque de rupture des anévrismes intracrâniens : caractérisation mécanique in vivo de la paroi artérielle." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2024. http://www.theses.fr/2024ECDL0011.
Intracranial aneurysms are a critical public health condition linked to the degradation of the cerebral artery wall. There is currently no method for estimating the risk of aneurysm rupture that takes into account the in vivo mechanical properties of the aneurysm wall, which are believed to be essential in the rupture phenomenon. This doctoral work is part of a large-scale project aimed at improving the intervention criteria currently available to practitioners by developing a non-invasive decision-support tool based on the mechanical state of the tissue to assess the probability of rupture. This tool will be based on the definition of a relationship between the shape of the aneurysm observed by clinical imaging and a database containing a set of clinical images from previous studies, associated with the in vivo mechanical properties of the wall and a characterisation of the rupture. To produce this database, an aneurysm wall deformation device was developed as part of the overall project. This doctoral work focuses on (1) the calibration, the optimisation and in vitro testing of this device on phantom arteries and (2) the in vivo application of the device on an animal model of intracranial aneurysm. To do this, a numerical model of the in vitro experiment was implemented and validated against the experimental results by developing an original validation method. This finite element model of fluid-structure interaction was used to understand the uncertainties involved in using the device within the aneurysm and to help for dimensioning the phantom arteries. The best compromise in terms of phantom artery wall thickness and flexibility was identified, taking into account the limitations of the fabrication techniques. In addition, an inverse analysis procedure was developed to estimate the mechanical characteristics of the aneurysm wall in vivo. Its use is based on quantifying the deformation generated by the device and visualised by spectral photon-counting computed tomography, an emerging medical imaging technique whose spatio-temporal resolutions allow controlled stressing of the tissue without increasing the risk of rupture. The mechanical properties identified were consistent with those derived from ex vivo characterisations of similar aneurysms available in the literature. Finally, a first patient-specific criterion for rupture of the aneurysm wall, taking into account the state of stress in vivo in the tissue, was proposed
Wehbi, Mickaël. "Modélisation de l'amorçage de la corrosion sous contrainte dans les alliages base nickel 182 et 82 en milieu primaire des réacteurs à eau sous pression." Thesis, Paris, ENMP, 2014. http://www.theses.fr/2014ENMP0056/document.
Nickel base welds are widely used to assemble components of the primary circuit of Pressurized Water Reactors (PWR) plants. International experience shows an increasing number of Stress Corrosion Cracks (SCC) in nickel base welds 182 and 82 which motivates the development of models predicting the time to SCC initiation for these materials. SCC involves several parameters such as materials, mechanics or environment interacting together. The goal of this study is to have a better understanding of the physical mechanisms occurring at grains boundaries involved in SCC. In-situ tensile test carried out on oxidized alloy 182 evidenced dispersion in the susceptibility to corrosion of grain boundaries. Moreover, the correlation between oxidation and cracking coupled with micro-mechanical simulations on synthetic polycrystalline aggregate, allowed to propose a cracking criterion of oxidized grain boundaries which is defined by both critical oxidation depth and local stress level. Due to the key role of intergranular oxidation in SCC and since significant dispersion is observed between grain boundaries, oxidation tests were performed on alloys 182 and 82 in order to model the intergranular oxidation kinetics as a function of chromium carbides precipitation, temperature and dissolved hydrogen content. The model allows statistical analyses and is embedded in a local initiation model. In this model, SCC initiation is defined by the cracking of the intergranular oxide and is followed by slow and fast crack growth until the crack depth reaches a given value. Simplifying assumptions were necessary to identify laws used in the SCC model. However, these laws will be useful to determine experimental conditions of future investigations carried out to improve the calibration used parameters
Perret, Adrien. "Étude du comportement en post-flambement d’un panneau de fuselage composite infusé avec structures intégrées." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0035/document.
These works are related to the numerical and experimental study of a composite stiffened panel, which is manufactured by a resin infusion process (Liquid Resin Infusion LRI). This manufacturing process allows structures to be integrated onto the skins of a panel being representative of a composite fuselage. Finite element models are built along with the numerical study, in order to deal with the post-buckling global behaviour of this panel. This leads to perfect a test set-up addressed during the experimental investigation. Several experimental methods are used to check the test panel and achieve the test. Material properties are also determined through material testing intended for the development of local numerical models, describing the integrated structures decohesion
Uguen, Alexandre. "Influence de l'endommagement plan sur le comportement hors-plan des composites stratifiés et des assemblages collés." Thesis, Brest, 2017. http://www.theses.fr/2017BRES0004/document.
Composite materials have been used in marine applications for decades for offshore windmills or even battleships because of its intrinsic properties which are assets for such applications (low weight, low magnetic signature...). Until now the composites used are almost made of glass fibers and polyester matrix. However the increasing demand for faster and lighter ships gradually leads manufacturers to turn to high performance composites made of carbon fibers and epoxy matrix. Using this new generation of material requires knowing the influence of the in-plane damage which can be due to water or mechanical damage on its out-of-plane strength. This study has shown a significant reduction of the out-of-plane failure envelope of the studied material after an extended stay in seawater until the saturation point.The out-of-plane tensile strength of the composite is very little affected by transverse cracking in the material whatever the aging state. Work has also been carried out on composite bonded assemblies and pointed out, on the one hand, the drop of the assembly strength because of the water aging and, on the other hand, the necessity to take into account the coupling between in-plane and out-of-plane damage for the prediction of the out-of-plane strength of such assemblies. Finally, different methods of prediction have been used to validate the experimental results confirming the importance to take into account the in-plane damage to predict the out-of-plane strength of composites and composite bonded assemblies
Le, Pavic Jérémy. "Méthodologie de dimensionnement d’un assemblage collé pour application aérospatiale." Thesis, Brest, École nationale supérieure de techniques avancées Bretagne, 2018. http://www.theses.fr/2018ENTA0001/document.
Space Launchers are complex structures composed of a large number of elements. The assembling of these components must show a high level of reliability. The use of adhesive bonding technology is an interesting solution since it presentsseveral assets compared to “classical” joint techniques (such as riveting, bolting and welding), mainly because it can help to construct lighter and less energy consuming systems However„ the implementation of adhesives also has somedrawbacks. Due to the strong variations of geometrical and material properties, stress concentrations appear at the extremities of the joint. This phenomenon; called edge effects; has a great influence on the failure of the bond. As a result, the simple use of a classical stress or energetic criteria is not appropriate to predict the fracture of such structures. Therefore, it is obvious that the design of bonded assemblies requires reliable tools to take the edge effects into account. In this work an incremental failure model, which combines the stress and energetic criteria, is used. In order to decrease the computational cost, a semi-analytical application of this model is proposed. This is intended to make the approach more interesting to be implemented in an industrial environment. The accuracy of the prediction of the failure load is enhanced by means of the Finite Element method. The reliability of both the semi-analytical and Finite Element approaches is verified by comparing the model predictions with experimental data issued from double-notched Arcan and tubular specimen geometries. The aim of the pre-design phase is to identify the critical area in the whole range of the application of the studied geometry. Therefore, the realization of a parametric study is required in order to build a response surface. In the present study, this has been achieved by means of spatial interpolation using the Kriging model
Guillou, Lionel. "Cell Mechanics : Mechanical Properties and Membrane Rupture Criteria." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX041/document.
Atherosclerosis is a chronic disease of the arteries that is a major cause of heart attacks and strokes. This thesis aims to provide novel insight into this disease by looking at specific factors involved in its development from a mechanical standpoint.Two important cell types involved in the development and progression of atherosclerosis are adherent endothelial cells and non-adherent leukocytes (white blood cells). We developed two devices that are able to measure the mechanical properties of both of these cell types. The first one, termed “profile microindentation”, uses micropipettes and microindenters to indent the cell, while the second one uses microfluidics to submit cells to an extensional stress.Further, we wondered if mechanics could help us understand when deformations undergone by cells, or stresses exerted on them, could become harmful.As a matter of fact, when atherosclerotic plaques occlude too much of the blood flow, the most common treatment consists of reopening the vessel with a balloon and keeping it open with a tubular wired mesh called a stent. This procedure exerts considerable compressive stress on the endothelium and is known to be associated with extensive endothelial damage. Hence, we seek to find a physical criterion that is predictive of endothelial cell membrane rupture under compression and to compare this to the stress exerted on the endothelium during the stenting procedure, to see if endothelial damage could potentially be avoided.Similarly, we seek to obtain a physical criterion that is predictive of leukocyte membrane rupture. We then compare and contrast the maximum possible deformations of leukocytes depending on whether those deformations are passive (such as when going through the microvasculature) or active (such as when leukocytes traverse the endothelial barrier)
Unfer, Ricardo Kirchhof. "Estudo da conformabilidade de chapas de aço IF da indústria automobilística." Universidade do Estado de Santa Catarina, 2015. http://tede.udesc.br/handle/handle/625.
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The new contributions of present thesis are an alternative experimental waviness method and a new theoretical model for evaluation of limit strains of sheet metal forming in the automotive industry, employing the analysis of roughness and waviness parameters evolution with the equivalent plastic strain and a new ductile rupture criterion as function of stress triaxiality. For validation of proposed experimental waviness method and rupture criterion, specimens of IF steel sheet of thickness 0.72mm, 0.82mm and 0.85mm were tested under tensile test and Nakazima sheet forming test with Marciniak flat punch. The specimens were deformed in incremental steps in different strain path such as: balanced biaxial stretching, plane strain, uniaxial tension and pure shear. Present proposed method consider that roughness and waviness parameters are important surface quality index and useful as indicator of onset of visible local necking and should be monitored in sheet metal forming. Thus, a Waviness Limit Curve, WLC, is proposed to be plotted in Map of Principal Limit Strains (MDLC) of sheet metal as an alternative to the forming limit strain curve, FLC. Various parameters of roughness and waviness such as arithmetic average roughness (Ra), maximum peak-valley roughness (Rt), arithmetic average waviness (Wa), total heigth peak-valley waviness (Wt), maximum peak height waviness (Pp) and maximum valley depth waviness (Pv) were measured during the uniaxial and biaxial testing. Tensile test of IF steel specimens at 0º, 45º and 90º to the rolling direction, RD, and Nakazima type of IF steel specimens at 0º RD only, in which a mesh of 2.5mm circles were printed, were employed. During the uniaxial and biaxial testing, the following plastic deformations were calculated in each straining step from the printed circles in the sheet surface: major true strain (1) and minor true strain (2). Parameters of roughness and waviness versus equivalent plastic strain curves were plotted to obtain a phenomenological equation of 4th and 3rd degree polynomials, using the Hill 1979 yield stress criterion. Furthermore, the growth rate of parameters Wa and Wt with equivalent plastic strain were calculated. From the growth rate, it was possible to conclude that the sheet 12 thickness imperfections, measured by Wa and Wt, evolve during material deformation, being possible to predict with accuracy the influence of equivalent plastic strain in the onset of local necking. From the experimental analysis, it was concluded that the maximum peak-valley waviness parameter (Wt) was the best option to chacaracterized the beginning of local necking in IF steel sheet forming. Thus, from the analysis of waviness growth rate parameters, Wa and Wt, during plastic strains, it was possible to propose a criterion of local necking inception. This allowed to obtain and plot an experimental Waviness Limit Curve (WLC) in the map MDLC: the beginning of local necking was established when the normalized parameter Wt* (=Wt/Wto) attained a critical value Wt*= 2.5, but with distinct values of equivalent strains. A second mathematical model was proposed for local necking criterion to obtain the FLC of IF steel sheets, employing stress triaxiality analysis and the Hill 1979 yield stress criterion. 2nd degree polynomials were obtained from plotted and adjusted phenomenological curves in graphs of equivalent strain at rupture versus stress triaxiality, considering the different plastic strain path in the formability testing. The IF steel specimens showed ductile rupture, according to scanning electronic microscope examinations, which showed that rupture occurred due to formation, growth and coalescence of large quantity of pores in many specimens of balanced biaxial (BB) and plane strain (DP). Also, mixed rupture of ductile type due to shear mechanisms in certain regions of tensile test (TS) and Nakazima uniaxial tension (UTN) specimens were shown.
As propostas de ineditismo da presente tese foram mostrar um método experimental alternativo de rugosidades e um modelo teórico de ruptura novo para se avaliar as deformações limites de conformação de chapas metálicas da indústria automobilística, empregando-se uma análise da evolução dos parâmetros de ondulação da rugosidade com a deformação plástica equivalente e um critério de ruptura dúctil em função da triaxialidade das tensões. Para validação do método experimental de rugosidades e do critério de ruptura propostos, utilizou-se corpos de prova de chapas de aço IF de 0,72mm, 0,82mm e 0,85mm de espessura, que foram submetidas aos ensaios de tração simples e ensaio de estampagem tipo Nakazima com punção plano de Marciniak. As amostras foram sujeitas a deformação incremental em diferentes trajetórias de deformação, tais como: estiramento biaxial balanceado, deformação plana, estiramento uniaxial e cisalhamento puro. O presente método proposto considera que parâmetros de rugosidade e ondulação são índices importantes de qualidade da superfície e servem como indicador preciso do início da estricção local visível e devem ser monitorados na conformação de chapas metálicas. Portanto, propõe-se traçar uma Curva Limite de Ondulação da Rugosidade, CLOR, no Mapa das Deformações Principais Limite de Conformação (MDLC) das chapas metálicas como alternativa da curva limite de conformação, CLC. Vários parâmetros do perfil de rugosidade e da ondulação da rugosidade tais como a rugosidade média aritmética (Ra), altura máxima pico-vale (Rt), ondulação média aritmética (Wa), a altura máxima da ondulação pico-vale (Wt), altura máxima de pico da ondulação (Pp) e profundidade máxima de vale (Pv) foram medidos durante os ensaios uniaxiais e biaxiais. Foram utilizados corpos de prova de aço IF em tração simples a 0º, 45º e 90º da direção de laminação, DL, e corpos de prova tipo ensaio Nakazima de aço IF somente a 0º DL nos quais foram impressos uma malha de círculos de 2,5 mm de diâmetro. Durante os ensaios uniaxiais e 10 biaxiais, as seguintes deformações plásticas foram calculadas em cada etapa a partir da malha de circulos impressos na superficie da chapa: a deformação verdadeira longitudinal maior (1) e a deformação verdadeira transversal menor (2). Curvas dos parâmetros de rugosidade e ondulações versus deformação plástica equivalente, empregando-se o critério de escoamento plástico de Hill (1979), foram traçados para se obter equações fenomenológicas do tipo polinomial de 4° e 3° graus. Além disso, foram calculadas as taxas de crescimento dos parâmetros Wa e Wt com a deformação plástica equivalente. A partir das curvas de taxas crescimento, foi possível concluir que as imperfeições na espessura da chapa, medidas por meio de Wa e Wt, evoluem durante a deformação do material, sendo possível prever com precisão a influência da deformação plástica equivalente no início do surgimento da estricção local. Concluiu-se então que o parâmetro da altura máxima total pico-vale das ondulações (Wt) é a melhor opção para caracterizar o início da estricção local em chapas de aço IF. Portanto, a partir da análise das taxas de crescimento dos parâmetros de ondulação, Wa e Wt, durante as deformações plásticas, foi possível propor um critério para o surgimento da estricção local. Isto permitiu obter e traçar a curva experimental de Limite de Ondulação da Rugosidade, (CLOR), no Mapa MDLC: o início da estricção local foi quando o parâmetro normalizado Wt* (=Wt/Wto) atingiu o valor crítico Wt*=2,5, mas com valores distintos da deformação equivalente. Um segundo modelo matemático foi proposto como critério de estricção local para obtenção da CLC de chapas de aço IF, empregando-se análise da triaxialidade de tensões e o critério de escoamento plástico de Hill (1979). Foram obtidos polinômios de 2º grau por meio de curvas fenomenológicas ajustadas e traçadas nos gráficos de triaxialidade de tensões versus deformação equivalente de ruptura, considerando-se as diferentes trajetórias da deformação plástica dos ensaios de conformabilidade. As amostras de chapa de aço IF mostraram ruptura dúctil conforme exame no microscópio eletrônico de varredura, o qual mostra que a fratura ocorreu devido a formação, crescimento e coalescência de uma grande quantidade de espaços vazios ou poros na maioria dos corpos de prova tipo Biaxial Balanceado (BB) e Deformação Plana (DP). Também, as amostras apresentaram fraturas mistas do tipo dúcteis e com mecanismos de cisalhamento em determinadas regiões das amostras fraturadas em Tração Simples (TS) e Tração Uniaxial de Nakazima (UTN).
Amestoy, Michel. "Propagation de fissures en elasticite plane." Paris 6, 1987. http://www.theses.fr/1987PA066238.
Chambard, Thierry. "Contribution à l'homogénéisation en plasticité pour une répartition aléatoire des hétérogénéités." Grenoble 1, 1993. http://www.theses.fr/1993GRE10004.
Linardon, Camille. "Etirage de tubes de précision pour applications biomédicales : contribution à l'analyse et l'amélioration du procédé par expérimentation, modélisation et simulation numérique." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00956588.
Karolak, Cyprien. "CarboFrac : Analyse et modélisation de l'engrenage (d'un siège auto) en acier à faible teneur en carbone carbonitruré." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM057/document.
This work aims at a better understanding and modeling of the failure of gradient metallic materials. It is applied to carbonitrided pinions made out of 20MnB5 steel, inserted in a "recliner", a safety mechanism of automotive seats. Carbonitriding induces high surface hardness while preserving significant core ductility. The experimental analysis of the fracture behavior of seat recliners in an industrial test confirmed the dual failure behavior of the component : brittle external layer, ductile core material. A test bench has been specifically designed for the project: one tooth is submitted to a lateral force until complete failure. In situ observations are performed and the load-displacement curve recorded, showing a variety of behaviors as a function of the teeth engagement depth and of the presence or not of the carbonitrided layer. Experimental tests with various tress states were conducted to measure plastic properties as well as to calibrate fracture criteria, for the carbonitrided layer and for the core steel. Von Mises plasticity and a simple strain hardening curve fit very well all these experiments. As fracture criteria from the literature were unable to predict failure correctly for all the mechanical tests, an adapted criterion has therefore been proposed as an outcome of this extensive mechanical testing campaign. Fracture simulation in LS Dyna has been performed using the element erosion technique, the limitations of which are discussed. Comparison with the experimental tooth fracture measurements allows evaluation of the proposed failure criteria, and enables to stress out and discuss the present limits of the simulation, concluding that it will be necessary in future work to account more finely for the mechanical property gradient together with the compressive residual stresses in the carbonitrided layer
Bugelli, Eduardo Barjud. "Modelos de falha em análise numérica de estrutura veicular submetida a impacto de baixa velocidade." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-13082010-165931/.
The aim of the present work is an assessment of several fracture models through experiments and numerical simulations. Tensile tests with notched and unnotched specimens were carried out to provide the material characterization in a wide range of stress triaxiality. The calibration of the parameters required by the fracture models was enabled by the parallel numerical simulation of the tensile tests, providing information on the stress and strain components at the failure locus. The constant equivalent strain criterion, the Johnson-Cook failure model and the maximum shear stress failure criterion were applied in a bumper beam impact case study. Several low speed impact tests were carried out in order to result in the components rupture. Numerical simulation of the experiments was performed using commercial finite element code LS-Dyna®. Good correlation of experiments and numerical simulations was achieved when considering this particular low speed case study.
Boukar, Ahmed. "Etude expérimentale et modélisation prédictive du comportement à l’impact des composites stratifiés." Electronic Thesis or Diss., IMT Mines Alès, 2022. http://www.theses.fr/2022EMAL0015.
This work consists of an experimental and numerical study of the behavior and strength of laminated composites subjected to a low velocity/low energy impact. The main objective is to develop a robust model capable of predicting the static and dynamic response of laminated composites, based on accurate experimental observations. Impact tests have been performed using a drop tower instrumented with high-speed cameras to monitor the evolution of damage in real time. The 3D finite element study of impact in explicit dynamics allows to judge the applicability of the failure criteria and the damage evolution methods. Various progressive damage models are implemented to predict the initiation and accumulation of damage in an NCF composite laminate. Cohesive elements are also inserted between adjacent plies to account for inter-ply delamination. In a second step, the model has been validated to reliably simulate the evolution of the mechanisms until failure, under quasi-static loading situations. In this case, the NCF composite is modeled using a unitary constitutive model at mesoscale, and presenting idealized regions of the polymer matrix and impregnated wicks. The idealized unitary model is defined on the basis of data from image analysis. The proposed methodology is generic, using a 3D elemental representation of the part for the global analysis, as well as the non-linearity of the matrix and the local response to the damage
Amann, Kurt André Pereira. "Metodologia semiempírica unificada para a estimativa da capacidade de carga de estacas." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/3/3145/tde-21102010-094919/.
The research starts from the fact that the semiempirical methods for estimating the pile load capacity shouldn\'t be used indiscriminately in any country\'s region without making proper adjustments to the local soil characteristics. It is verified, from this, that there are no specific methodologies to make such adjustments and the geotechnical engineers find themselves forced to perform a simple classification of the methods in \"conservative\" or \"against the safety\", which constitutes a form of paradigm. In this context, this paper proposes a Unified Semiempirical Methodology (MSU) in three steps. In the first, the designer estimates the foundation load capacity from the optimization of best practices adopted by different semiempirical methods used in Brazil. A discussion is also made the toe embedment and the creation of new semiempirical methods. In the second step, the verification of the foundation performance is carried out, based on the failure criteria applied to the load-settlement curve of load tests. At this step, the inaccuracies from that paradigm are outlined and a new proposal is made for applying the failure criteria. In the third step, a backanalysis is accomplished to admeasure the unified semiempirical estimative from the first step. It is, thus, proposed to separate both shaft friction and toe resistance from the total load, by means of load transfer methods, and by the proposal of polynomial adjustments in the case of instrumented piles. With the critical analysis of this process, a new mathematical approach to load transfer is presented. The correction of the coefficients of the semiempirical methods is made by the application of the Soils\'s Hierarchy concept (AMANN, 2000). The results of semiempirical methods correction, however, are specific to the soils of each particular site. The applicability, of the proposed methodology, is illustrated using pile load tests from various parts of the country.
Charrier, Jean-sebastien. "Développement de méthodologies dédiées à l’analyse robuste de la tenue de structures composites sous chargements complexes tridimensionnels." Thesis, Paris, ENSAM, 2013. http://www.theses.fr/2013ENAM0004.
Composite materials, particularly unidirectional laminates, are increasingly used for the design of airplane structures because of their interesting mass/rigidity/strength ratio. Their use is now extended to the design of primaries structures (in metallic so far) for the future range of aircrafts. In those primaries structures, lots of composite components are subjected to complex out-of-plane loadings such as L-angle structures. The main failure mechanism encountered is delamination in the radius mainly due to the applied out-of-plane loadings. Nevertheless, the main weakness of the unidirectional laminates is their out-of-plane mechanical properties and the prediction of this failure mode in laminated structures (subjected to 3D loadings) remains a scientific challenge. It is thus necessary to propose an innovative 3D failure approach, physically based, and the associated identification procedure for the out-of-plane strengths. The aim of this Phd-thesis is thus to propose a 3D strength analysis method dedicated to 3D loadings and matching the requirements of a design office (low time of computation and easy to identify and to carry out). A 3D progressive failure approach which permits to predict damages and failure modes encountered in laminated structures has been proposed. The out-of-plane strengths (tensile and shears) are identified through the analysis of tests performed on L-angle structures, representative of the final aeronautical components. Finally, some unfolding/folding tests on L-angle specimens have been performed in order to validate the proposed 3D failure approach
Oliveira, Alex Duarte de. "Soil mechanical behavior artificially cemented: essays modeling and application." Universidade Federal do CearÃ, 2015. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=15769.
Considerando a semelhanÃa existente entre o comportamento mecÃnico dos solos artificialmente cimentados e dos maciÃos rochosos, o presente trabalho propÃe uma metodologia para a obtenÃÃo das envoltÃrias de resistÃncia dos solos artificialmente cimentados, utilizando o critÃrio de ruptura geral de Hoek-Brown. A metodologia proposta consiste, basicamente, em realizar dois ensaios triaxiais, um com o solo nÃo cimentado e outro com o solo cimentado com um teor de cimento elevado, e estimar as envoltÃrias de resistÃncia para os teores de cimento intermediÃrios, atravÃs das equaÃÃes desenvolvidas. Para o desenvolvimento da metodologia, inicialmente, foram realizados ensaios de compressÃo simples e triaxiais nÃo drenados, com o objetivo quantificar a influÃncia do fator vazio/cimento (n/Civ) sobre os parÃmetros de resistÃncia das misturas cimentadas utilizadas. A partir dos resultados dos ensaios de resistÃncia e da equaÃÃo geral do critÃrio de Hoek-Brown, foram desenvolvidas equaÃÃes para calcular os parÃmetros da envoltÃria (a, m, s), em funÃÃo do fator vazio/cimento. A metodologia proposta foi aplicada aos resultados dos ensaios triaxiais apresentados em outros quatro trabalhos e os resultados mostraram que a envoltÃria de Hoek-Brown à adequada para representar a resistÃncia dos solos artificialmente cimentados, sendo capaz de incorporar os efeitos causados pela tensÃo confinante e pelo nÃvel de cimentaÃÃo. As envoltÃrias estimadas e as obtidas com os ensaios triaxiais ficaram bem prÃximas, indicando que a metodologia proposta pode ser empregada com um razoÃvel grau de confiabilidade. Os resultados obtidos com a metodologia proposta foram utilizados para simular, atravÃs do MÃtodo dos Elementos Finitos, o comportamento carga-recalque e a variaÃÃo do fator de seguranÃa de uma fundaÃÃo superficial assente sobre um sistema de dupla camada, sendo a superior cimentada. As simulaÃÃes foram realizadas utilizando como variÃveis o teor de cimento da camada reforÃada e a relaÃÃo entre a altura da camada cimentada (H) e o diÃmetro da fundaÃÃo (D). Os resultados obtidos mostram que a utilizaÃÃo de camadas artificialmente cimentadas eleva consideravelmente as tensÃes verticais necessÃrias para um recalque relativo especÃfico e, tambÃm, o fator de seguranÃa da fundaÃÃo. Com isso, a execuÃÃo de fundaÃÃes superficiais, em substituiÃÃo a fundaÃÃes profundas, torna-se viÃvel.
Kamgaing, Somoh Georges Bertrand. "Conception et caractérisation mécanique des pièces en matériaux composites moulées par compression." Thesis, Paris, ENMP, 2013. http://www.theses.fr/2013ENMP0081/document.
If the use of composite materials is already effective on elements of main structures and large size parts, their generalization to secondary parts is not effective due to their cost and their performances compared to metals. The framework of this thesis is to contribute to the establishment of a French chain of high performance composite parts at low cost. Thus, it was initially question of optimizing the process vis-à-vis the main composite materials used in the aerospace structures. Then, the molded laminates were characterized and the effects of severe conditions (humidity, temperature, impact) on their mechanical behavior were studied. Also, reduce the cost of parts also means reducing the safety factors which remain very high. This requires a better prediction of the failure and the mechanical behavior beyond the linear. Taking the five harness satin weave carbon/PEEK material as example, non-linear phenomena (viscoplasticity), damage mechanisms and failure criteria were studied, with particular emphasis on the delamination. The possibility to perform finite element analysis of the parts directly at the mesoscopic scale (ply-scale) was also explored and suggests promising expectations for a less conservative sizing of composite structures
Couture, Cyrille. "Caractérisation du comportement mécanique de grès poreux en condition triaxiale vraie : déformation diffuse et localisée, effet de l'anisotropie." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALI058.
The objective of this doctoral thesis consists in the characterization of diffuse and localized deformations during monotonic loading of both isotropic and anisotropic porous sandstones. In particular, the kinematics of emerging and persistent strain localization structures are investigated in a combination of complementary experimental, analytical and numerical approaches, exploring the effect of different true triaxial loading paths in the octahedral plane.A series of experimental loading tests have been performed in a laboratory environment comprising a high pressure true triaxial apparatus (TTA), which is designed to provide access to full-field measurements of one of the sample surfaces at high spacial and temporal resolutions. Important developments contributed in this work enabled to extend the capabilities for this apparatus to perform invariant controlled loading paths, while acquiring direct strain measurements from a combination of strain gauges and digital image correlation (DIC). Using this apparatus, two experimental campaigns have been realized, focusing on the mechanical characterization of both a well-studied isotropic Vosges sandstone and a newly studied anisotropic Vosges sandstone. The later sandstone has been selected for the organization of its granular fabric in thin bedding plane layers of variable porosity. The results from these series of mechanical loading experiments contribute an original insight into the emergence and development of localized deformation during different stages of loading. A combined analysis is performed on the evolution of the macroscopic stress-strain responses, full-field measurements of incremental strains through DIC, as well as post-mortem x-ray tomography. Additionally, in this investigation exploring rarely considered loading paths, the independent role of the mean stress, the Lode angle and the orientation of the bedding planes is systematically studied according to their respective influence on the material strength, the manifestation of localized structures and the transition towards a ductile behavior of the material.In terms of analytical development, a bifurcation analysis is proposed for a novel three invariant model, validated with experimental results obtained for the isotropic sandstone. This theoretical model, proved to be successful in predicting both the deformation band inclination and the dilatancy angle of the material at failure.In parallel, a double scale model based on numerical homogenization is presented. In this approach, a macro 2D finite element model (FEM) is coupled to a micro 3D discrete element model (DEM) at the particle scale of a representative elementary volume (REV) in the frame of a hierarchical scheme (FEMxDEM), with second gradient regularization. This model is extended in the scope of this work to the study of cemented granular materials, with the development of a frictional-cohesive damageable contact law, implemented at the DEM level. In an extensive series of true triaxial loading simulations, the hierarchical numerical model is used to explore both the influence of different micro-structural arrangements (DEM) and heterogeneities at the sample scale (FEM). In this respect, two types of anisotropies resulting from heterogeneities defined at each scales are further investigated. The mechanical response and localized deformation, emerging from the micro-scale constitutive model, is shown to display significant correspondence with experimental observations in the studied Vosges sandstones.This combination of advanced experimental, analytical and numerical studies contributes a unique insight into important and open questions regarding the mechanical response and deformation processes of cemented granular materials
Jaafar, Mohamed. "Étude expérimentale et simulation numérique de l’usinage des matériaux en nids d’abeilles : application au fraisage des structures Nomex® et Aluminium." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0303/document.
The use of sandwich structures made with honeycomb core and skins has considerably increased these last years in several industrial sectors such as aeronautics, aerospace, naval and automotive. This growing interest for the alveolar materials is mainly related to their low density and better mass/stiffness/strength ratio compared to metal alloys or conventional composites. However, their constitution makes machining operations complicated and difficult to control because of the premature cutting tool wear and the significant damage induced in the workpiece. In fact, the important vibrations of the thin honeycomb walls are a source of several problems such as the poor surface quality, uncut fibers, delamination, defects, etc. This work deals with the understanding of the honeycomb composites behavior and metallic during machining. The material removal process by milling of these materials presents several scientific and technological challenges. Firstly, an experimental analysis has been used to identify the physical phenomena involved during the chip formation process and generated by the interactions between the cutting edge and the honeycomb cell walls. A particular interest was focused on the characterization of defects induced in the material by different parts of the cutter, the shredder and the saw blade. Two experimental protocols have been set up to qualify the quality and integrity of the machined surface. They consider the particularity of the honeycomb cores: composite or metallic, their geometry, and the thin wall thickness. A new quality criterion has been established and proposed as a damage indicator to monitoring the machining process and choice optimal cutting conditions. Based on Taguchi's statistical analysis, a hierarchy of the machining parameters and their influence on the behavior of these materials have then realized. In addition, the wear of cutting tools has been studied according to the selected tool-material couple and milling conditions. The optimization of machining parameters is often long and expensive only via experimental approach. Modelling and numerical simulation can provide complementary support with an interesting numerical tool to analyze the physics of cutting honeycombs. In this perspective and in the second part of the PhD thesis, a finite element numerical model has been especially developed for the 3D milling operation. For Nomex®, two coupled mechanical-damage behavior laws have been identified and implemented in Abaqus explicit subroutine VUMAT. To simulate the chip formation process and induced subsurface damage, two fracture criteria (Hashin and Tsai-Wu) with stiffness degradation concept have been operated. The comparison between the numerical simulation results and experimental data shows a good agreement in terms of the chip formation mechanisms, cutting forces and damage modes
Salloum, Joulia. "Comportement mécanique de Matériaux Sandwichs Innovants pour application nautique." Electronic Thesis or Diss., IMT Mines Alès, 2023. http://www.theses.fr/2023EMAL0017.
This work consists of an experimental and numerical study of the mechanical behaviour of sandwich composite materials used in the nautical industry, up to damage occurrence and its evolution. For eco-design purposes, the facings are made of NCF triaxial basalt fibre laminates and a partially bio-sourced resin (greenpoxy), and the core consists of recycled PET foam. In addition to preparing these materials via vacuum infusion and conducting their microstructural and mechanical characterisation, the main goal of this study is to develop a robust model capable of predicting the response of these sandwich materials under static loading. It is worth noting that all conducted mechanical tests, including compression of the foam alone, simple traction of the monolithic in different directions, or bending of the sandwich composite, are instrumented by image correlation on multiple sides of the specimen to monitor the real-time damage evolution. Furthermore, a 3D finite element study of the mechanical response of the single components (foam and monolithic) and the sandwich is carried out based on Abaqus® simulations to assess the applicability of failure criteria and damage evolution methods. For instance, regarding the foam, the "crushable foam" model was used to predict its collapse within the sandwich structure. As for the monolithic, a progressive damage model of the fibre/matrix constituents is adopted within each ply, and cohesive elements between adjacent plies are used to account for delamination on a mesoscopic scale. This methodology aims to predict the initiation and accumulation of damage in the laminate. The proposed methodology is generic and provides an evolving basis for introducing the concept of cohesion between fibre and matrix, the effectiveness of which is intended for evaluation
Jaafar, Mohamed. "Étude expérimentale et simulation numérique de l’usinage des matériaux en nids d’abeilles : application au fraisage des structures Nomex® et Aluminium." Electronic Thesis or Diss., Université de Lorraine, 2018. http://www.theses.fr/2018LORR0303.
The use of sandwich structures made with honeycomb core and skins has considerably increased these last years in several industrial sectors such as aeronautics, aerospace, naval and automotive. This growing interest for the alveolar materials is mainly related to their low density and better mass/stiffness/strength ratio compared to metal alloys or conventional composites. However, their constitution makes machining operations complicated and difficult to control because of the premature cutting tool wear and the significant damage induced in the workpiece. In fact, the important vibrations of the thin honeycomb walls are a source of several problems such as the poor surface quality, uncut fibers, delamination, defects, etc. This work deals with the understanding of the honeycomb composites behavior and metallic during machining. The material removal process by milling of these materials presents several scientific and technological challenges. Firstly, an experimental analysis has been used to identify the physical phenomena involved during the chip formation process and generated by the interactions between the cutting edge and the honeycomb cell walls. A particular interest was focused on the characterization of defects induced in the material by different parts of the cutter, the shredder and the saw blade. Two experimental protocols have been set up to qualify the quality and integrity of the machined surface. They consider the particularity of the honeycomb cores: composite or metallic, their geometry, and the thin wall thickness. A new quality criterion has been established and proposed as a damage indicator to monitoring the machining process and choice optimal cutting conditions. Based on Taguchi's statistical analysis, a hierarchy of the machining parameters and their influence on the behavior of these materials have then realized. In addition, the wear of cutting tools has been studied according to the selected tool-material couple and milling conditions. The optimization of machining parameters is often long and expensive only via experimental approach. Modelling and numerical simulation can provide complementary support with an interesting numerical tool to analyze the physics of cutting honeycombs. In this perspective and in the second part of the PhD thesis, a finite element numerical model has been especially developed for the 3D milling operation. For Nomex®, two coupled mechanical-damage behavior laws have been identified and implemented in Abaqus explicit subroutine VUMAT. To simulate the chip formation process and induced subsurface damage, two fracture criteria (Hashin and Tsai-Wu) with stiffness degradation concept have been operated. The comparison between the numerical simulation results and experimental data shows a good agreement in terms of the chip formation mechanisms, cutting forces and damage modes
Maziz, Ammar. "Analyse des endommagements dans les pipes en matériaux composites." Electronic Thesis or Diss., Brest, École nationale supérieure de techniques avancées Bretagne, 2021. http://www.theses.fr/2021ENTA0019.
Damage modelling of hybrid composite materials has played an important role in the design of composite structures. Although numerical models for the progressive damage of filament wound hybrid composite pipes such, matrix cracking, delamination, and fiber failure have been developed in the literature; there is still a need for improvement. This thesis aims to develop damage models suitable for predicting dynamic behaviour and intra-laminar and inter-laminar damage in hybrid composite tubes under internal pressure subjected to dynamic loading such as the impact of an external object. Fracture mechanics and continuum damage mechanics approaches were adopted to build the damage model. A detailed analysis was performed to have an overview of all the damage mechanisms until the final failure. Cohesive elements were inserted into the two-dimensional and three-dimensional models to simulate the initiation and propagation of matrix cracking and delamination in cross-layered laminates. The damage model was implemented in the FE code (Abaqus/Explicit) by a user-defined material subroutine (VUMAT). Subsequently, validations based on test/calculation correlations on real subsystems and/or parts were performed. Damage initiation was predicted based on the stress-strain failure criteria, while the damage evolution law was based on the dissipation of failure energy. The nonlinear behavior of the material in shear was also taken into account and validated against experimental/numerical results. The predictions show excellent agreement with the experimental observations
Yu-ChiChang and 張育齊. "Study on The Three Dimensional Failure Criterion of Yutenping Sandstone to Evaluate It’s Rupture Pressure for Carbon dioxide Geological Storage." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/27637393367853828073.
國立成功大學
土木工程學系碩博士班
101
In order to reduce the emission of carbon dioxide, technology of carbon dioxide geological storage has been adopted by many countries widely. The theory is that injecting carbon dioxide in the form of Supercritical fluid into the layer such as old oil reservoirs, underground coal seams, and deep saline formations. While in the process of injection, the pressure of supercritical carbon dioxide must be greater than the fluid pressure existing in the stratum, this might cause new rupture in the rock layer, or induce the slide of rock layer by existing fault, both of whom are likely leading to carbon dioxide’s leaking out. The site in this study, Miao Li Tiechen Shan gas storage pit is one of the fit sites for carbon dioxide geological storage in Taiwan. Because the west of Taiwan are receive the extruding of Eurasian Plate and Philipenis Sea Plate, the in-situ stress conditions are complex, and the conditions of traditional triaxial test will ignore the intermediate principal stress, which means σ_2=σ_3. Thus, this study use improved triaxil cell to get the strength variation in the principle stress situation (σ_1≠σ_2≠σ_3) of Yutenping sandstone, which is the storage layer of geological storage by hollow cylinder triaxial test, and moreover the three dimensional failure criterion, which can be reference for further geological storage operations. This study also use improved triaxil cell to do hydraulic fracture test of original Yutenping sandstone and the specimen that had been during accelerate mineralization storage mechanism to get the rupture pressure of geological storage. At last, according to the establish three dimensional failure criterion to estimate the rupture pressure of Yutenping sandstone of Tiechen Shan in different depth.
Charrier, Jean-Sebastien. "Développement de méthodologies dédiées à l’analyse robuste de la tenue de structures composites sous chargements complexes tridimensionnels." Thesis, 2013. http://www.theses.fr/2013ENAM0004/document.
Composite materials, particularly unidirectional laminates, are increasingly used for the design of airplane structures because of their interesting mass/rigidity/strength ratio. Their use is now extended to the design of primaries structures (in metallic so far) for the future range of aircrafts. In those primaries structures, lots of composite components are subjected to complex out-of-plane loadings such as L-angle structures. The main failure mechanism encountered is delamination in the radius mainly due to the applied out-of-plane loadings. Nevertheless, the main weakness of the unidirectional laminates is their out-of-plane mechanical properties and the prediction of this failure mode in laminated structures (subjected to 3D loadings) remains a scientific challenge. It is thus necessary to propose an innovative 3D failure approach, physically based, and the associated identification procedure for the out-of-plane strengths. The aim of this Phd-thesis is thus to propose a 3D strength analysis method dedicated to 3D loadings and matching the requirements of a design office (low time of computation and easy to identify and to carry out). A 3D progressive failure approach which permits to predict damages and failure modes encountered in laminated structures has been proposed. The out-of-plane strengths (tensile and shears) are identified through the analysis of tests performed on L-angle structures, representative of the final aeronautical components. Finally, some unfolding/folding tests on L-angle specimens have been performed in order to validate the proposed 3D failure approach