Dissertations / Theses on the topic 'Multiaxia'

Modéliser la réponse mécanique des matériaux consiste à établir une relation (un modèle) entre contraintes et déformations,dépendant de paramètres identifiés à partir de données expérimentales issues d’essais mécaniques. D’une part, l’identification basée sur des essais homogènes n’apporte pas d’information sur la réponse du matériau soumis à des sollicitations complexes. D’autre part, l'identification basée sur des essais multiaxiaux est plus coûteuse numériquement et impose le choix du modèle a priori. Récemment, a émergé la possibilité de représenter le comportement mécanique des matériaux par une base de données plutôt que via une loi de comportement au travers de la « Data Driven Computational Mechanics ». Dans ce cadre, l’algorithme Data-Driven Identification (DDI) développé par Leygue et al. (2018) permet d’estimer le champ de contrainte lors d’un essai multiaxial.Cette thèse propose d’explorer la réponse cinématique puis mécanique complète de membranes élastomères sollicitées en grandes déformations multiaxiales grâce à un montage expérimental original mettant en jeu un hexapode. La méthode DDI est ensuite utilisée pour déterminer la réponse en contraintes du matériau lors de ces essais. Deux développements sont finalement proposés : une méthode d’identification alliant DDI (sans modèle) et modèles de comportement, et une proposition d’amélioration des géométriesd’éprouvettes pour les essais multiaxiaux
Modeling the mechanical response of materials involves the derivation of a relationship (a model) between stresses andstrains, depending on parameters. These parameters are identified from experimental data obtained from mechanical tests. On the one hand, identification based on simple tests (uniaxial tension, for example) provides no information on the response of materials subjected to complex loading conditions. On the other hand, identification based on multiaxial tests is more costly numerically and requires the model to be chosen at the outset of the procedure. Recently, the possibility of representing themechanical behaviour of materials by a database rather than via a behaviour law has emerged through "Data-Driven Computational Mechanics". On this basis, the Data-Driven Identification (DDI) algorithm developed by Leygue et al. (Computer Methods in Applied Mechanics and Engineering, 331, 184-196 (2018)) can be used to estimate the stress fieldduring a multiaxial test. The present thesis explores the complete kinematic and mechanical response of elastomer membranes subjected to multiaxial large strain, using an original experimental set-up involving a hexapod. The DDI method is then used to determine the stress response of the material during these multiaxial tests. Two developments are finally presented: an identification method combining DDI (model-free) and standard constitutive models, and a proposal forimproving sample geometries for multiaxial tests

Le comportement spécifique des Alliages à Mémoire de Forme (AMF) est dû à une transformation de phase appelée transformation martensitique. Cette transformation de phase peut être activée par des variations de température mais aussi par des chargements mécaniques. Si le comportement 1D de ces alliages est bien connu, la modélisation du comportement de ces alliages sous sollicitations multiaxiales complexes pose encore quelques problèmes. Dans un premier temps, nous nous intéressons à la validation expérimentale directe d'une relation entre la fraction volumique de martensite et la déformation de transformation qui est utilisée dans de nombreux modèles. Pour cela des essais en traction-compression-torsion avec suivi de résistance électrique sur un AMF de type Cu-Al-Be sont réalisés. Ces essais mettent en évidence les effets de la texture de ces alliages sur leur comportement. Par ailleurs, des simulations numériques de type micro-macro sont réalisées, pour différentes textures et pour différents trajets multiaxiaux proportionnels. Ces simulations complètent, d'une part, la base de données expérimentale, et permettent, d'autre part, de valider les hypothèses retenues pour la modélisation. Enfin, des essais anisothermes de traction compression torsion proportionnels et non proportionnels sont réalisés sur un AMF de type Ni-Ti. Une surface de début de réorientation de phase R est ainsi mise en évidence
The specific behaviour of Shape Memory Alloys (SMA) is due to a solid-solid transformation called martensitic transformation. This reversible transformation consists mainly in a shear without volume change and is activated either by stress or temperature. Despite all the properties of SMA are well known for one-dimensional mechanical loadings, the modelling of the 3D behaviour remains difficult. In a first step, we consider the experimental validation of a conjecture concerning the proportionality of the equivalent transformation strain with the martensite volume fraction. Therefore we perform tension-compression-torsion tests coupled with electrical resistance measurements on a Cu-Al-Be SMA. The behaviour of this alloy is sharply influenced by its crystallographic texture. Otherwise, numerical simulations on different textures and for several multiaxial loadings are performed. The experimental database is so completed in order to validate the choices made for the modelling. Finally, we perform several tension-torsion proportional and non-proportional, non-isothermal tests on a Ni-Ti SMA. The existence of an equivalent stress, able to describe the yield stress for phase-R reorientation is so highlighted

An experimental study has been carried out to investigate the behaviour of rock under multiaxial compression and assess the influence of both the stress conditions and test configuration on the apparent characteristics of this behaviour. Over three hundred specimens of Springwell sandstone, of various forms, have been tested using different loading techniques and most encountered stress fields. Cubes and thick-walled hollow cylinders have been subjected to uniaxial, biaxial, triaxial and polyaxial compression, and solid cylinders have been subjected to standard uniaxial and triaxial compression. Extensive work has initially been put into designing and developing the testing facilities required. A new multiaxial hollow cylinder test apparatus has been devised using a Hoek triaxial cell and specially designed system for the application of internal pressure, major modifications have been made to an existing multiaxial cubical test apparatus, and appropriate testing arrangements and procedures have been developed. Prior to initiating the experimental programme, characterisation tests have been conducted to determine the fundamental properties of the rock, and non-destructive ultrasonic wave velocity tests have been utilised together with statistical methods to examine any inherent variations in the specimens used. A remarkable agreement has emerged between the rock static and dynamic Young's moduli and the results have confirmed that the Springwell sandstone can practically be regarded as linear elastic, homogeneous and isotropic. The concept of the multiple failure state triaxial test has been utilised and extended to conduct multiple failure state polyaxial tests. While the concept remains useful, strain results obtained beyond the first failure state are likely to be inconsistent. Results of cube tests have been found to be highly influenced by the boundary conditions. Although the use of PTFE sheets can reduce the effect of friction between the specimen and the loading platens, it may equally have a weakening effect on the test specimen. The theory of elasticity has been found adequate to calculate the stresses in the hollow cylinders but remains inexact when deviation from linear behaviour occurs prior to failure. When the outer and inner surfaces of the cylinder are not perfectly concentric, the effect on the test results has proved negligible. Hollow cylinders have been found to provide an alternative means for measuring the rock indirect tensile strength. Results of biaxial and polyaxial tests on both cubes and hollow cylinders have confirmed the marked influence of the intermediate principal stress on the apparent strength of rock. Comparison of results from multiaxial tests on cubes, hollow and solid cylinders have shown that the apparent strength, deformability and failure characteristics of the rock are remarkably influenced by the stress conditions imposed as well as the test configuration used. Available failure criteria have advantages and disadvantages, but none of them can explain the diversity of the results obtained. On the whole, the results appear to cast doubt on common conceptions of rock failure and ultimately pose the question of how realistic current testing techniques are in their prediction of the actual behaviour of rock.

The multiaxial deformation of magnesium alloys is important for developing reliable, robust models for both the forming of components and also analysis of in service performance of structures, for example, in the case of crash worthiness. This work presents a combination of unique biaxial experimental tests and biaxial crystal plasticity simulations using a visco-plastic self-consistent (VPSC) formulation conducted on AZ80 magnesium alloy in two different conditions - extruded and a more weakly textured as cast condition. The experiments were conducted on tubular samples which are loaded in axial tension or compression along the tube and with internal pressure to generate hoop stresses orthogonal to the axial direction. The results were analyzed in stress and strain space and also in terms of the evolution of crystallographic texture. In general, it was found that the VPSC simulations matched well with the experiments, particularly for the more weakly textured cast material. However, some differences were observed for cases where basal < a > slip and {10¯12} extension twinning were in close competition such as in the biaxial tension quadrant of the plastic potential. The evolution of texture measured experimentally and predicted from the VPSC simulations was qualitatively in good agreement. Finally, experiments and VPSC simulations were conducted in which samples of the extruded AZ80 material were subjected to a small uniaxial strain prior to biaxial loading in order to further explore the competition between basal slip and extension twinning.

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2006.
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O objetivo deste trabalho é o estudo de critérios de resistência à fadiga multiaxial de metais em regime de alto número de ciclos. Os modelos apresentados por vários autores propõem, como medidas principais, a contribuição das tensões normais e das tensões cisalhantes para a degradação por fadiga do componente, além dos parâmetros do material. A questão que se coloca no contexto de solicitações multiaxiais é: qual é a melhor medida para caracterizar a amplitude de tensões cisalhantes e como incorporar o efeito das tensões normais? O estudo desenvolve então, uma análise destas questões relacionadas à modelagem de um critério de resistência à fadiga. Tensões normais trativas contribuem de forma maléfica para a degradação por fadiga por agirem no processo de abertura de microtrincas; quase a totalidade dos modelos de fadiga multiaxial considera a tensão hidrostática como medida das tensões normais atuantes na solicitação à fadiga. Sabe-se que esta é basicamente uma média das tensões normais e propõe-se aqui a substituição desta, pela máxima tensão principal. A aplicação da proposta a um conjunto grande de resultados experimentais disponíveis na literatura confirmou a hipótese de que a pior situação, que corresponde à existência de uma micro-trinca ortogonalmente orientada à máxima tensão principal, deve ser considerada e fornece uma previsão de resistência à fadiga mais conservativa e portanto, a favor da segurança. Quanto às tensões cisalhantes, primeiro apresentam-se as propostas de alguns autores, destacando-se dentre elas a abordagem do envelope elíptico e do envelope prismático. As duas aproximações fornecem as mesmas boas previsões de resistência à fadiga para dados experimentais de carregamentos senoidais com ciclos de mesma freqüência. Avança-se a análise para carregamentos mais gerais cujas trajetórias se distanciam da forma de um elipsóide e verifica-se de maneira inédita que, para uma ampla faixa de histórias de carregamento, as medidas de amplitude de tensões cisalhantes obtidas pelo máximo envelope prismático são equivalentes às medidas correspondentes obtidas pelo mínimo envelope elíptico. Tal verificação foi comprovada considerando-se trajetórias com ciclos senoidais assíncronos proporcionais e fora de fase, e ciclos não senoidais selecionadas a partir de resultados experimentais relativos a situações limites de resistência à fadiga. ________________________________________________________________________________________ ABSTRACT
The aim of this work is to evaluate multiaxial high cycle fatigue criteria for metals. The models presented by many authors propose that the the normal and shear stresses are the main variables controlling the fatigue damage, as well as the materials parameters. In the multiaxial context, the fundamental question to be answered is: which is the best measure to characterize the shear stress amplitude and how the well known effect of the mean normal stresses can be incorporated in the modeling process? This work carries out an analysis of such issues! Tensile stresses reduce the fatigue strength of metals as they keep the crack faces opened. Almost the totally of the multiaxial fatigue models available in the literature considers the hydrostatic stress as a measure for the normal stresses acting upon the fatigue solicitation. The hydrostatic stress is basically an average of the normal stresses acting in three orthogonal planes passing through a material point. Here we claim that the worst situation in terms of fatigue solicitation corresponds to the existence of a micro-crack orthogonally oriented to the maximum principal stress. Therefore, the maximum principal stress rather than the hydrostatic stress should be considered as an appropriate measure of the mean normal stress effect on the fatigue solicitation. To validate this hypothesis available experimental data published in the literature were selected and compared with the estimates provided by a modified version of the Prismatic Hull criterion developed by Mamiya and Araujo. Concerning the shear stresses, some models which consider the Minimum Circunscribing Ellipsoid or the Maximum Prismatic Hull of the deviatoric stress path as an appropriate measure for the shear stress amplitude are presented. The analysis carried out considering different materials subjected to a broad range of loading paths involving sinusoidal loadings with distinct frequencies and non-harmonic loadings revealed the shear stress amplitudes measured by the prismatic hull are equivalent to the ones measured by the elliptic hull.

Eine nachträgliche Verfestigung von nähgewirkten multiaxialen Gelegen führt zu einer verbesserten Ausnutzung der Verstärkungsfadeneigenschaften. Zu diesem Zweck wurden Lösungsansätze für eine entsprechende Verfestigungseinrichtung gesucht und bewertet. Drei Anlagenvarianten wurden durch die Kombination verschiedener Verfahren (Strahlungswärme, die Kombination aus Wärme und Druck sowie Walzenbeschichtung) und Bindemittel (Thermoplaste in verschiedenen Aufmachungen, Beschichtungsmassen) entworfen. Sie bieten auf die Einsatzzwecke Produktion, Laborbetrieb und geringster Aufwand abgestimmte Eigenschaften
The additional stabilization of open grid warp knits provides a better exploitation of the reinforcing yarns. To realize such an additional stabilization, various possible methods have been examined and assessed. Three different types of stabilization installations have been developed by combining the most promising technologies (infrared radiation, combination of heat and pressure, roll coater) and binding agents (thermoplastics, liquid agents). These installations offer special fea-tures for different needs: production, laboratory and least expense

Ces travaux de thèse concernent l’effet des hétérogénéités microstructurales sur la tenue en fatigue multiaxiale à grand nombre de cycles (FGNC) d’alliages d’Al-Si de fonderie utilisés dans un contexte automobile. Les hétérogénéités microstructurales caractéristiques de cette famille de matériau sont la matrice d’aluminium (souvent caractérisée à l’aide la DAS et/ou la SDAS et du niveau de durcissement par précipitation), les inclusions (particules de silicium, intermétalliques) et les défauts de fonderie (films d’oxyde et surtout porosités).Afin de découpler clairement ces effets, trois nuances d’alliages d’aluminium de fonderie obtenues à l’aide de différents procédés (coulée en coquille, coulée par procédé à moule perdu) et associées à plusieurs traitements thermiques (T7, Compression isostatique à chaud (CIC)) ont été étudiées. Le traitement CIC a en particulier été employé afin d’obtenir une microstructure exempte de pore. Une vaste campagne d’essais en FGNC a été conduite pour quatre modes de chargement : uniaxial (R=-1), torsion (R=-1), traction-torsion combinées (R=-1) et traction équibiaxiale (R=0.1). Les effets sur le comportement en FGNC ont été identifiés pour les matériaux avec et sans pores : effet de la multiaxialité pour les chargements à R=-1, effet de la contrainte moyenne et effet de la biaxialité en traction biaxiale à R=0.1. Une attention particulière a été portée à la caractérisation des mécanismes d’endommagement dans l’objectif de mettre en évidence le role des pores, de la matrice d’aluminium, des inclusions dans les mécanismes d’endommagement, et ceci pour les différentes modes de chargement.Deux approches analytiques ont ensuite été proposées. La première concerne la modélisation de l’effet de volume sollicité sur la tenue en fatigue sous chargement uniaxial en présence de pore en se basant sur une approche de prédiction de la taille maximale de pore dans un volume donné. La seconde, basée sur une approche probabiliste, est dédiée à la simulation du diagramme de Kitagawa-Takahashi pour différents modes de chargement. Ces deux approches conduisent à des résultats en accord avec l’expérience, ceci pour les différents matériaux et conditions étudiées.La dernière partie propose une analyse 3D par éléments finis de l’effet des pores sur la résistance en fatigue. L’analyse repose sur l’utilisation de la géométrie réelle des pores, obtenue à l’aide d’observations en micro-tomographie RX 3D. Ce travail a pour but d’évaluer la possibilité de prédire la limite de fatigue à l’échelle macrosopique à partir de la réponse mécanique "locale" au voisinage des pores critiques
This work treats the influence of the microstructural heterogeneities on the multiaxial high cycle fatigue (HCF) strength of cast aluminium alloys used in an automobile context. The characteristic microstructural heterogeneities present in this family of materials are the aluminium matrix (often characterised by the SDAS and/or the DAS and the precipitation hardening level), inclusions (silicon particles and intermetallics) and casting defects (oxide films and casting porosity).In order to clearly decouple these effects, three cast Al-Si alloys, obtained thank to different casting processes (gravity die casting and lost foam die casting) and associated with several heat treatments (T7 and Hot isostatic pressing-HIP), have been investigated. The HIP treatment is used in order to obtain a porosity free alloy. A vast experimental HCF campaign, including four loading modes (uniaxial (R=-1), torsion (R=-1), combined tension-torsion (R=-1) and equibiaxial tension (R=0.1)) has been undertaken. The following effects on the HCF behaviour have been characterised for the porosity free alloy as well as porosity containing alloys: (a) the effect of the multiaxiality (for the loading modes at R=-1), (b) the effect of the mean stress and (c) the effect of the biaxality (for equibiaxial tensile loads at R=0.1). The fatigue damage mechanisms have been studied in order to highlight the roles of the casting pores, the aluminium matrix and the inclusions on the fatigue damage mechanisms.Two analytical fatigue models are proposed. The first one concerns the effect of the loaded volume on the uniaxial fatigue strength of the porosity containing alloys using an approach to predict of the maximum pore size in a given volume. The second model, based on a probabilistic approach, takes into account the competition between the different observed damage mechanisms and leads to a Kitagawa-Takahashi type diagrams for different loading modes. It is shown that these analytical models result in good predictions for the three materials investigated and the four loading modes.A numerical study, presented in the last section, is related to the 3D finite element analysis of real pores. Real pore geometries are obtained thank to micro-tomography observations. The principal aim of this study is to evaluate the possibility of predicting the fatigue strength at the macroscopic scale thanks to the local mechanical behaviour around critical pores

Dieser Beitrag bietet einen Überblick über die in zwölf Jahren Forschungsarbeit am Institut für Textilmaschinen und Textile Hochleistungswerkstofftechnik (ITM) erzielten Ergebnisse auf dem Gebiet textiler Betonbewehrungen unter Einsatz der Nähwirktechnik. Standen zunächst die Weiterentwicklung der Nähwirk- bzw. Multiaxial-Kettenwirktechnik und die Integration zusätzlicher Prozessschritte im Mittelpunkt, so wurde dies mit der Einführung neuer Faserwerkstoffe durch die Beantwortung grundlegender Fragen zum Materialverhalten von Glas- und Carbonfasern unter verschiedensten Belastungsszenarien ergänzt. Aufbauend auf den gewonnen Erkenntnissen stehen heute Multiaxialgelege als Bewehrung für Beton zur Verfügung, die ein weites Anforderungsspektrum abdecken können, mit hoher Qualität und Produktivität herstellbar sind und damit den praktischen Einsatz des Textilbetons auf breiter Basis ermöglichen
This paper provides an overview on the results of textile concrete achieved in twelve years of research at the Institute of Textile Machinery and High Performance Material Technology (ITM) in the field of textile reinforcements for concrete based on the multiaxial stitch-bonding technology. During the early years the research focused on the development of the textile manufacturing process and the integration of additional functions in stitch-bonding machines. With the introduction of new fiber materials this was shifted towards the description of the material behavior of glass and carbon fibers under different load scenarios. Based on the results of this research, multiaxial multi-ply fabrics are available now as reinforcements for concrete, covering a broad range of applications. These fabrics can be produced with high quality and productivity and enable the practical usage of textile reinforced concrete

Despite real applications having complex triaxial loading, current physical test methods to predict component behaviour are mainly uniaxial. But previous work has indicated that there may be substantial differences between the rubber's uniaxial and biaxial behaviour and hence through incompressibility, its triaxial properties. In order to quantify these differences equipment was developed to assess the biaxial performance of selected rubber compounds using inflated circular diaphragms. Although allowing higher extensions than stretching a sheet in its own plane, such tests do not allow stress and strain to be measured directly, requiring careful marking of the sample, or calculation through simulation. On the grounds of perceived accuracy, the latter was chosen, requiring accurate, general, elastic constants to high extensions. In this thesis the development of this apparatus, along with the associated techniques is described, along with the development of a new elastic theory. The tests on this new apparatus indicated significant differences between the uniaxial and biaxial strength and fatigue of rubber. In a unimdal test natural rubber (NR) is much stronger than styrene butadiene rubber (SBR) below 35pphr of carbon black. In a biaxial test though the converse is true, although there is some evidence of crystallinity in NR during the biaxial test. Distinct differences were also found in fatigue between the two load cases. When plotted against extension ratio the biaxial life of SBR was found to increase, while the converse is true for NR. However if life is plotted against a function of strain energy, the biaxial life of both polymers increases for a given energy.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTITUIÇÕES COMUNITÁRIAS DE ENSINO PARTICULARES
Eixos de virabrequim estão sujeitos a carregamentos multiaxiais quando em serviço. Por se tratar de um estado complexo de tensões, os modelos aplicados na determinação da vida em fadiga de tais componentes devem permitir, também, uma abordagem multiaxial, mais avançados do que aqueles adotados para carregamentos uniaxiais. O objetivo deste trabalho foi prever a falha em serviço de eixos virabrequins de unidades geradoras Diesel ou gás de plantas termoelétricas. Falhas recentemente ocorridas em eixos virabrequins no parque termoelétrico nacional justificam o presente estudo, para garantir eficiência e segurança nas operações industriais. Com base no método de elementos finitos, foram calculadas as tensões atuantes em um eixo virabrequim de unidade geradora a gás, com 10 mancais, duas bielas por mancal e fabricado com aço estrutural DIN 34CrNiMo6. Em sequência, adotando-se estas tensões atuantes calculadas, foram aplicados diversos critérios de fadiga para prever sua falha. Para tal, adotaram-se os modelos de Papadopoulos, Findley, Matake, McDiarmid, Carpinteri e Spagnoli, Liu e Mahadevan, Mises, Sines e Crossland, todos de fadiga de alto ciclo, baseados no plano crítico ou na tensão de von Mises. Propriedades de resistência à fadiga do material foram retiradas da literatura. Os resultados obtidos indicaram que o componente é seguro quando avaliado usando tais critérios.
Crankshaft axles are subject to multiaxial loading when in service. Because the resulting state of stresses is complex, models applied to determining the fatigue life of such components employ a multiaxial approach as well, more advanced than those adopted for uniaxial loads. The objective of this work is to predict the failure in service of crankshafts of diesel or gas generating units of thermoelectric plants. Crankshafts reported recent failures in the national thermoelectric power plant justifies the present study, to guarantee efficiency and safety in such industrial operations. Based on the finite element method, the resulting stresses on a DIN 34CrNiMo6 structural steel gas generating unit crankshaft, with 10 bearings, two connecting rods per bearing were calculated. Using these finite element calculated stresses, several fatigue criteria were applied to predict this cranckshaft structural failure. Models due to Papadopoulos, Findley, Matake, McDiarmid, Carpinteri and Spagnoli, Liu and Mahadevan, Mises, Sines and Crossland, all of high cycle fatigue based on the critical plane or von Mises strain, were adopted. Material fatigue properties used in the analyses were compiled from specidized literature. Obtained results indicated that the component considered is safe regarding fatigue loadings, as evaluated using such criteria.

In the introduction to a recent symposium on rolling contact fatigue, R.A.Smith stated that it was difficult to apply our greatly increased understanding of metal fatigue, to rolling contact fatigue, because of "the apparent lack of alternating tensile stresses to drive the cracks." He went on to say "alternating shear stresses are easily found, but the reproduction of continuous crack growth controlled by shear (Mode II in fracture mechanics terms), has proved to be near impossible." This project has demonstrated that under specific conditions this mode of growth does occur. The project began by studying rolling contact fatigue defects, in particular the 'squat' defect in railway lines, and the stress analyses that have been performed on them. It was concluded that the largest stress cycle experienced by the cracks must be a shear stress. It. series of tests were then performed that loaded a crack in pure shear, or a mixture of tension and shear, looking at the effects of using fully reversed shear loading, and the effects of applying tensile mean stresses to reduce the friction on the crack flanks. However these tests all produced less than one millimetre of mode II growth, before the cracks arrested or branched. The final series of tests however applied a tensile load cycle before each shear load cycle. This time coplanar growth was produced, that is the crack grew in the direction of the maximum shear stress. This type of load cycle is a simplification of the load cycle calculated by Bower and Johnson of Cambridge University, where the tensile load is produced by fluid trapped in the crack. Two crack growth rate formulae were produced that fitted the data, indicating that the growth rate was dependent on both the tensile and the shear parts of the cycle.

Eine nachträgliche Verfestigung von nähgewirkten multiaxialen Gelegen führt zu einer verbesserten Ausnutzung der Verstärkungsfadeneigenschaften. Zu diesem Zweck wurden Lösungsansätze für eine entsprechende Verfestigungseinrichtung gesucht und bewertet. Drei Anlagenvarianten wurden durch die Kombination verschiedener Verfahren (Strahlungswärme, die Kombination aus Wärme und Druck sowie Walzenbeschichtung) und Bindemittel (Thermoplaste in verschiedenen Aufmachungen, Beschichtungsmassen) entworfen. Sie bieten auf die Einsatzzwecke Produktion, Laborbetrieb und geringster Aufwand abgestimmte Eigenschaften.
The additional stabilization of open grid warp knits provides a better exploitation of the reinforcing yarns. To realize such an additional stabilization, various possible methods have been examined and assessed. Three different types of stabilization installations have been developed by combining the most promising technologies (infrared radiation, combination of heat and pressure, roll coater) and binding agents (thermoplastics, liquid agents). These installations offer special fea-tures for different needs: production, laboratory and least expense.

Static and dynamic behavior of the dry and saturated Ottawa sand are studied in the constitutive modeling laboratory, by using cubical multiaxial device with servo-controlled loading system and high speed automatic data acquisition system. In this investigation, the multiaxial cubical device with servo-controlled loading system and high speed automatic data acquisition system is used to apply independently the three-dimensional loading and measure corresponding strains and stress. The cubical multiaxial device is modified to include the servo-controlled pressure system and automatic data acquisition system. To understand the cyclic behavior and post cyclic behavior, comprehensive laboratory tests have been performed on the dry and saturated Ottawa sand, covering a number of relative densities and confinements.

Le comportement spécifique des Alliages à Mémoire de Forme (AMF) est dû à une transformation de phase appelée transformation martensitique. Cette transformation de phase peut être activée par des variations de température mais aussi par des chargements mécaniques. Si le comportement 1D de ces alliages est bien connu, la modélisation du comportement de ces alliages sous sollicitations multiaxiales complexes pose encore quelques problèmes.
Dans un premier temps, nous nous intéressons à la validation expérimentale directe d'une relation entre la fraction volumique de martensite et la déformation de transformation qui est utilisée dans de nombreux modèles. Pour cela des essais en traction-compression-torsion avec suivi de résistance électrique sur un AMF de type Cu-Al-Be sont réalisés. Ces essais mettent en évidence les effets de la texture de ces alliages sur leur comportement.
Par ailleurs, des simulations numériques de type micro-macro sont réalisées, pour différentes textures et pour différents trajets multiaxiaux proportionnels. Ces simulations complètent, d'une part, la base de données expérimentale, et permettent, d'autre part, de valider les hypothèses retenues pour la modélisation.
Enfin, des essais anisothermes de traction compression torsion proportionnels et non proportionnels sont réalisés sur un AMF de type Ni-Ti. Une surface de début de réorientation de phase R est ainsi mise en évidence.

Modélisation du comportement du béton sous des charges multiaxiales avec une loi incrémentale non linéaire. Simulation numérique d'essais uniaxiaux, biaxiaux et triaxiaux. Comparaison avec les résultats expérimentaux obtenus avec une presse biaxiale.

De nouvelles approches phénoménologiques sur la modélisation du comportement des AMFs sont nécessaires pour tenir en compte leur réponse complexe sous chargement multiaxial. L’effet de l’anisotropie induit une dépendance de leur comportement inélastique de la direction du chargement pour des cas superélastiques. La réorientation martensitique affecte drastiquement la réponse du matériau sous chargement non-proportionnel. La charge répétitive modifie aussi certaines propriétés du matériau. L’objectif de cette étude est de proposer un nouveau modèle constitutif thermodynamique robuste pour les AMFs, focalisé surtout sur des compositions NiTi équiatomiques pour capter la transformation martensitique anisotrope et la réorientation des variantes martensitiques. Une nouvelle approche mathématique est introduite pour permettre la prise en compte de l’anisotropie de contraintes et l’évolution des déformations inélastiques lors de la transformation directe, causée par les conditions de mise en forme de structures en AMFs. Cette méthode est évaluée en employant des courbes contraintes-déformations résultant de chargements proportionnels simulés par un modèle micromécanique. Un modèle phénoménologique considérant surtout la réorientation martensitique et mettant en évidence le fort couplage thermomécanique est développé. Il est implémenté dans une plate-forme numérique en C++, SMART+, et évalué en exécutant des simulations des expériences non-proportionnelles existantes. Des structures complexes sont également simulées en employant la Méthode des Élements Finis. La dernière partie de ce travail concerne l’étude expérimentale des effets du chargement cyclique sur l’évolution des déformations résiduelles et le seuil de transformation des alliages NiTi sous sollicitation uniaxiale et biaxiale
New phenomenological approaches in modeling the behavior of SMAs are needed to account for their complex response under multiaxial loading. The effect of anisotropy induces a dependence of their inelastic behavior to the direction of the loading for superelastic cases. Martensitic reorientation affects drastically material response under non-proportional loading. Repeated loading also alters certain material properties. The goal of this study is to propose a new robust thermodynamic constitutive model for SMAs with focus on equiatomic NiTi compositions to capture anisotropic martensitic transformation and reorientation of martensitic variants, always taking in mind the strong thermomechanical coupling. A new mathematical approach is introduced to account for the anisotropy of stresses and the evolution of inelastic strains during forward transformation caused by the forming conditions of SMA structures. This method is evaluated by utilizing stress-strain curves resulting from proportional loading simulated with a micromechanical model. A phenomenological thermodynamic model considering especially martensitic reorientation and exhibiting the strong thermomechanical coupling is developed. It is implemented on a numerical platform in C++, SMART, and evaluated by simulating existing non-proportional experiments. Complex structures are also simulated using Finite Element Analysis. The last part of this work concerns the experimental study of the effects of cyclic loading to the evolution of residual strain and transformation threshold of NiTi under uniaxial and biaxial testing

Registra mediante la aplicación del modelo de diagnóstico multiaxial de la CIE 10, además de la enfermedad biomédica motivo de la hospitalización, la presencia de patología mental, de limitaciones funcionales como consecuencia de la enfermedad y de factores sociales y circunstanciales que influyen en la salud, en el 30% o más de los pacientes hospitalizados en un Servicio de Medicina del Hospital Guillermo Almenara Irigoyen - EsSalud. El estudio es descriptivo, observacional y transversal realizado en una muestra de pacientes hospitalizados en el Servicio de Medicina Interna N°1, del Hospital Nacional Guillermo Almenara, en el período comprendido entre el 1° de agosto de 2014 y el 31 de octubre de 2014. Para la interpretación de las variables se usaron distribuciones de frecuencia absoluta y relativa (%). Resultados: el 51.5% de los pacientes seleccionados presentaban trastornos mentales, el 97% compromiso funcional como consecuencia de la enfermedad y el 87.9% factores sociales y circunstanciales que afectan el estado de salud. Se concluye que mediante la aplicación del modelo de diagnóstico multiaxial, ha sido posible registrar además de la patología biomédica, la presencia de patología mental, de limitaciones funcionales como consecuencia de la enfermedad y de factores sociales y circunstanciales que influyen en la salud, en más del 30% de los pacientes hospitalizados en un Servicio de Medicina del Hospital Guillermo Almenara.
Tesis

Les travaux de cette thèse s’intéressent au comportement mécanique d’une mousse destinée à l’absorption d’énergie dans une assise de siège pilote. Les méthodes de caractérisation habituelles proposent de solliciter le matériau suivant une seule direction. Cependant, cette caractérisation ne permet pas d’être représentatif des sollicitations lors de l’utilisation de l’assise, qui sont multiaxiales. Cette étude s’intéresse donc à la caractérisation du comportement multiaxial d’une mousse. L’approche originale utilisée est une séparation du comportement en deux contributions: changement de volume (pression-volume) et de forme (distorsion-cisaillement). Un premier moyen d’essais de compression hydrostatique a été développé afin de caractériser le changement de volume. Les résultats mettent en évidence une forte influence de la contribution en changement de volume, lors d’une sollicitation de compression uniaxiale. Un deuxième moyen d’essais a été développé permettant d’appliquer des sollicitations radiales suivant un angle cinématique ϑε, imposant une proportion de volume et de distorsion. Les résultats montrent une forte influence de l’angle cinématique sur les comportements des contributions de changement de volume et de forme. D’autres sollicitations impliquant de la compression et du cisaillement d’une manière séquentielle ont montré une influence du niveau de volume sur le comportement en changement de forme. Enfin, un modèle de simulation 2D par assemblage d’éléments finis 1D, montre une bonne représentation des différents comportements des contributions de changement de volume et de forme obtenus expérimentalement
This thesis is focused on the mechanical behavior of foam designed to absorb energy in an airplane pilot seat cushion. Usually, these materials are characterized using uniaxial compressive test. Nevertheless, this uniaxial characterization doesn’t represent the real in-use loading of cushion. To complete these data, this work focuses on multiaxial behavior characterization of foam. The analysis of behavior is realized by using a separation into two contributions linked to the volume (pressure-volume) and the shape (distortion-shear) change. A hydrostatic testing system was developed with the aim to characterize the volume change behavior. Results highlight a strong influence of the volume change behavior during an uniaxial compression solicitation. A second testing system was developed allowing to apply radial solicitations following a kinematic angle, which imposes a non-proportional variation of volume and distortion. A kinematic angle influence is observed on the volume and shape change behavior. Other solicitations composed of compression and shear applied in a sequential way, permit to observe a volume influence on the shape change behavior. Finally, a 2D simulation model composed of 1D element composition shows a good representation of the volume and shape changes behavior obtained from experimentation

Ce travail de thèse, en partenariat avec l’entreprise ALSTOM, s’inscrit dans une logique de remplacement de pièces industrielles en alliage métallique par des pièces composites pour l’allègement des structures. L’objectif est de contribuer à l’écriture de règles de dimensionnement permettant au partenaire industriel de certifier des pièces structurales annulaires réalisées en composite à matrice thermoplastique thermostable (TPTS) renforcée par des fibres de carbone pour des applications embarquées sur machine tournante. Il s’agit plus exactement de déterminer la durée de vieen fatigue de ces pièces, en particulier en présence d’endommagement, et lorsque celles -ci sont soumises aux chargements inertiels et thermiques de service.Au cours de ce travail de thèse, une méthodologie a été développée afin de répondre à cette demande. La stratégie a consisté à reproduire,à l’échelle d’éprouvettes de laboratoire, l’état de contrainte multi-axial et l’endommagement auxquels la structure industrielle est soumise, et ce en développant et optimisant un essai de traction sur des éprouvettes annulaires entaillées. Les essais multi axiaux plus classiques mettant en œuvre des sollicitations par pression interne présentent effectivement de nombreux problèmes techniques et sécuritaires lorsqu’ils doivent être mis en œuvre à chaud.Une fois la configuration d’essai sur anneau optimisé par simulation numérique, des essais ont été réalisés afin de confirmer l’apparition des endommagements escomptés à l’aide de techniques de contrôle non-destructif. Les essais cycliques réalisés dans cette configuration ont montré une excellente résistance du matériau en fatigue, en particulier pour un ratio de chargement R de 0.5, proche des conditions de service. Les résultats ont également soulignés le fort potentiel restant de ces structures, même après un grand nombre de cycles de chargement
The objective of this thesis work, in partnership with ALSTOM Company, is to contribute to the writing of design rules in order to qualify and certify annular structures made of thermostable thermoplastic matrix composite reinforced by carbon fibre. These structures are used in rotating machines for embedded applications.This work proposes an innovative methodology to achieve this goal. It consists in reproducing, at the scale of a laboratory specimen, the multiaxial stress and damage states to which the industrial structure is subjected in-service byoptimizing a tensile test on annular notched specimen. More conventional multiaxial tests, based on internal pressureand tensile loading are particularly unsafe and difficult to be performedwhen implemented at elevated temperature.After the optimisation of the ring configuration by numerical simulation, experimental tests were performed to validatethe appearance of the expected damage under loading. Damage was characterized using non-destructive techniques suchas acoustic emission and infrared thermography. The cyclic tests achieved using this configuration showed high fatiguestrength of this material, in particular for a ratio R of 0.5 (equivalent to thein-service ratio). The results also highlight thegreat remaining strength and rigidity of these structures, even after a large number of cycles

Ce travail a été entrepris dans le cadre d’une coopération internationale entre l’Université de Brasilia, l’Agence spatiale brésilienne (AEB), l’ENS Paris-Saclay et le groupe SAFRAN. L’objet principal de cette coopération est l’étude du fretting-fatigue, problème de contact associé à des charges de fatigue qui réduisent considérablement la durée de vie des composants en raison de la concentration élevée de contraintes, de l’usure et des conditions de chargement non proportionnelles. En ce qui concerne les coûts de calcul élevés impliqués dans l’évaluation des applications industrielles, l’un des objectifs de ce travail est d’améliorer les performances des simulations de frettage utilisant une approche d’enrichissement. L'idée est de tirer parti du fait que les champs mécaniques autour des bords de contact dans des configurations de contact cylindriques dans des conditions de frottement sont similaires à ceux trouvés près du fond de fissure dans les problèmes de mécanique de rupture élastique linéaire. Cette similitude rend attrayante l’idée d’enrichir les simulations de frettage par éléments finis via le framework X-FEM, ce qui nous permet de travailler avec des maillages plus grossiers tout en conservant une bonne précision. Comme nous le montrerons dans ce travail, il est possible de travailler avec des maillages jusqu'à 10 fois plus grossiers que si une méthode par élements finis classique était utilisée, permettant une forte amélioration des performances de calcul.Ce travail étudiera également l’influence de la prise en compte des effets de l’usure dans la prévision de la durée de vie en fatigue. Par conséquent, des simulations par éléments finis du fretting-fatigue ont été effectuées en tenant compte de la mise à jour de la géométrie due à l'enlèvement de matière et les résultats ont été comparés aux données expérimentales et aux simulations par éléments finis dans lesquels les effets de l'usure ont été négligés (stratégie simplificatrice généralement adoptée pour évaluer les problèmes de fatigue de frottement). Les critères de fatigue multiaxiaux conventionnels associés à la théorie des distances critiques ont été utilisés pour prédire la vie. Les résultats ont montré que, pour les données évaluées ici, lorsque des essais de fretting-fatigue ont été menés sur un alliage Ti-6Al-4V dans des conditions de glissement partiel, considérer les effets de l'usure pourraient augmenter légèrement la précision des prévisions de durée de vie. Cependant, cette amélioration n’est peut-être pas digne d’intérêt si nous prenons en compte les coûts de calcul élevés dans les analyses d’usure
This work has been undertaken in the context of an international research cooperation between the University of Brasilia, the Brazilian Space Agency (AEB), the ENS Paris-Saclay and the SAFRAN group. The main subject of this cooperation is the investigation of fretting fatigue, which is a contact problem in conjunction with fatigue loads responsible for reducing considerably components’ fatigue life due to the high stress concentration, wear and non-proportional loading conditions involved in such problems. Regarding the high computational costs involved when assessing industrial applications, one of the aims of this work is to improve the performance of fretting simulations making use of an enrichment approach. The idea is to take advantage of the fact that the mechanical fields around the contact edges in cylindrical contact configurations under fretting conditions are similar to the ones found close to the crack tip in linear elastic fracture mechanics problems. This similarity makes attractive the idea of enriching finite element fretting simulations through the X-FEM framework, which enables us to work with coarser meshes while keeping a good accuracy. As it will be shown in this work, it is possible to work with meshes up to 10 times coarser than it should be if a conventional FE method was used allowing a strong improvement of the computational performances.This work will also investigate the influence of considering wear effects in the prediction of fretting fatigue lives. Therefore, fretting fatigue FE simulations have been carried considering the geometry update due to the material removal and results were compared to both experimental data and FE simulations where wear effects were neglected (simplifying strategy usually adopted when evaluating fretting fatigue problems). Conventional multiaxial fatigue criteria in association with the Theory of Critical Distances have been used in order to predict life. Results have shown that, for the data here assessed, where fretting fatigue tests were conducted on a Ti-6Al-4V alloy under partial slip conditions, considering wear effects might slightly increase the accuracy of life predictions. However, this slight improvement may not be worthwhile regarding the increase in the computational cost when compared to standard approaches where wear is neglected

Depuis le XXème siècle, le développement continu des puissances de calcul a permis aux méthodes numériques de devenir essentielles dans le processus de conception des produits industriels. La méthode de calcul par éléments finis apporte aux industriels des solutions fiables pour anticiper avec précision la tenue mécanique des composants sans recourir aux prototypages réels. La tendance actuelle d’optimisation des coûts de fabrication impacte directement la conception des produits avec notamment comme axe de travail la réduction des épaisseurs de matière. Dans ce contexte, les pièces de structures sont moins robustes qu’avant. La maitrise de la tenue en fatigue des composants est devenue aujourd’hui un enjeu majeur. Ce phénomène complexe se montre sensible à l’histoire vécu par la matière, notamment en ce qui concerne les potentiels impacts sur les propriétés matériaux locales des différents procédés de fabrication intrinsèques au composant. Le procédé de soudage induit des conséquences à plusieurs niveaux de l’assemblage qui peuvent s’avérer être néfastes pour la durée de vie des structures. Ces phénomènes multi-physiques d’origine thermique, métallurgique et mécanique doivent alors être pris en compte comme données d’entrée dans les études en fatigue pour fiabiliser les résultats. Cependant, la complexité des données d’entrée et les temps de traitements très conséquents freinent leur utilisation par les ingénieurs lorsqu’il s’agit de structures de grandes dimensions. Afin de répondre aux besoins des industriels, deux développements ont été créés pour réduire le temps d’analyse des approches de Manson-Coffin et de Fatemi-Socie de près de 99,9%. Ces post-traitements font partie intégrante d’une stratégie originale de dimensionnement en fatigue chainant la prise en compte des effets locaux des procédés d’assemblage, et permettant ainsi l’analyse en fatigue des grandes structures dans un délais compatible avec les attentes des bureaux d’études
Since the 20th century, the continuous development of computing power has enabled numerical methods to become essential in the design process of industrial products. The finite element calculation method provides manufacturers with reliable solutions for accurately anticipating the mechanical strength of components by limiting the number of prototypes. The current trend of reducing manufacturing costs has a direct impact on product design with, in particular, the reduction of material thicknesses. In this context, the structural parts are more exposed to the risk of rupture. Controlling the fatigue behavior of components has now become a major challenge. This complex phenomenon is sensitive to the history experienced by the material, particularly with regard to the impacts on the local material properties by the various manufacturing processes. The welding process induces consequences at several levels of the assembly which can prove to be harmful for the life of the structures. These multi-physical phenomena of thermal, metallurgical and mechanical origin must then be taken into account as input data in fatigue studies to make the results more reliable. However, the complexity of the input data and the very substantial processing times hamper their use by engineers when dealing with large structures. In order to meet the needs of manufacturers, two developments have been created to reduce the analysis time of the Manson-Coffin and Fatemi-Socie approaches by nearly 99.9%. These post-processings take part of an original fatigue dimensioning strategy linking the consideration of the local effects of assembly processes, and thus allowing the fatigue analysis of large structures within a timeframe compatible with the industrial context

La première étape d'un calcul de durée de vie en fatigue oligocyclique consiste à obtenir l'historique des contraintes et des déformations sur des points jugés critiques. Pour éviter des calculs complets par éléments finis (force brute) particulièrement longs, les corrections élasto-plastiques locales évaluent ces historiques en un temps très court. Les approches existantes manquant de précision, une nouvelle méthode de calcul qui s'inspire des modèles d'homogénéisation a été proposée. Elle a été implémentée dans le code de calcul ZéBuLoN et validée sur des cas de charge quelconques en multiaxial non proportionnel aléatoire, ce qui n'est le cas d'aucune autre méthode de la littérature. Ces historiques servent d'entrée aux méthodes de prévision de durée de vie. Un nouvel algorithme de comptage de cycles a été utilisé pour extraire une série de cycles d'un chargement multiaxial aléatoire. Il s'agit d'une technique de rainow qui permet de conserver toutes les composantes du chargement, et de définir un "cycle" dans l'espace des contraintes déviatoriques. Des calculs de durée de vie ont été réalisés pour évaluer la pertinence de l'ensemble de la chaîne de calcul ainsi constituée. On montre pour finir des applications à une pièce industrielle (bras de châssis de grue).

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.
Includes bibliographical references (p. 93-100).
This thesis presents the design, development, and construction of an instrument for biaxial mechanical testing of inhomogeneous elastic membranes. The instrument incorporates an arrangement of linear motion stages for applying arbitrary deformation profiles on the material under test, purpose-built two-axis force transducers for high-resolution measurement of applied loads, and a digital imaging system for full-field strain measurement. The components described herein provide the foundation for a sophisticated biaxial testing platform for determining the mechanical properties of anisotropic, inhomogeneous membrane materials.
by Ariel Marc Herrmann.
S.M.

Orientador: Auteliano Antunes dos Santos Júnior
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-16T12:18:17Z (GMT). No. of bitstreams: 1 Minucci_FredericoRodrigues_M.pdf: 2447535 bytes, checksum: 1f8099b913d0c77861627fd93867cfb4 (MD5) Previous issue date: 2010
Resumo: O virabrequim é um dos principais componentes do motor de combustão interna e sua função é, em conjunto com a biela, transformar o movimento de translação do pistão em movimento de rotação. Como sofrem carregamentos cíclicos durante toda sua vida útil, o principal tipo de falha de um virabrequim é por fadiga. Porém, por estarem sujeitos a carregamentos complexos, tensões multiaxiais são geradas resultando no problema da fadiga multiaxial. Nos últimos anos, diversos métodos que tratam desse problema foram apresentados, porém, até hoje, nenhuma abordagem foi universalmente aceita. Este trabalho apresenta a avaliação da vida de dois virabrequins fornecidos pela empresa Thyssen Krupp Metalúrgica Campo Limpo Ltda quanto à falha por fadiga utilizando os critérios de fadiga multiaxial para elevado número de ciclos de Matake, McDiarmid e DangVan, baseados nos planos críticos, e os critérios de Sines, Crossland e Kakuno-kawada, baseados nos invariantes de tensão. Ao longo do trabalho, é descrita a cinemática e a dinâmica do movimento de um virabrequim bem como uma forma adequada de tratamento para a vibração torcional. Com base nos esforços, é feita a análise de tensões através do método de superposição de esforços unitários. Os resultados das tensões são utilizados como entradas em um algoritmo especialmente desenvolvido para os critérios de fadiga citados. As análises feitas mostram que os projetos analisados são seguros quando avaliados utilizando tais critérios
Abstract : The crankshaft is one of the most important components of the internal combustion engine and its function is, with the rods, transforming the linear movement of the piston into rotation. As it is under cyclic loading during all of his life, the main type of failure in these components is due to fatigue. However, as they are subject to complex loads, multiaxial stresses arise, which results in the problem of multiaxial fatigue. Recently, several approaches to this problem were proposed but until now, there is no universally accepted approach. This work evaluates the life of two designs of crankshafts provided by Thyssen Krupp Metalúrgica Campo Limpo Ltda with respect to the fatigue failure using the multiaxial high-cycle fatigue criteria of Matake, McDiarmid and Dang Van, based on critical planes, and Sines, Crossland and Kakuno-Kawada, which are based on the stress invariants. Throughout the work it is described the kinematics and the dynamics of the cranckshaft movement and an appropriate form of treatment for the torsional vibration. Based on the loads, a stress analysis is performed using the finite elements method and the superposition principle. The resulting stresses are used as inputs in a specially developed algorithm to evaluate the fatigue criteria cited. These analyses show that the designs are safe when they are evaluated using such criteria
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

In spite of many multiaxial fatigue life prediction methods proposed over decades of research, no universally accepted approach yet exists. A multiaxial fatigue damage model developed for approximately proportional random amplitude loading is proposed in this study. A normal strain based analysis incorporating the multiaxial state of stress is conducted along a critical orientation assuming a constant strain ratio. The dominant deformation direction is chosen to be the critical orientation which is selected with the help of a principal strain histogram generated from the given multiaxial loading history. The uniaxial cyclic stress-strain curve is modified for the biaxial state of stress present along the critical orientation for the plane stress conditions. Modified versions of Morrow's and of Smith, Watson, and Topper's (SWT) mean-stress models are used to incorporate mean stresses. A maximum shear strain based analysis is, in addition, conducted to check for the shear dominant fatigue crack growth possibility along the critical direction. The most damaging maximum shear strain is chosen after analyzing the in-plane and the two out-of-plane shear strains.

The minimum of the two life values obtained from SWT model and the shear strain model is compared with the life estimated by the proposed model with the modified Morrow's mean stress model. The former is essentially the life predicted by Socie. The results of the proposed model, as reduced to the uniaxial case, are also compared with the experimental data obtained by conducting one-channel random amplitude loading history experiments.
Master of Science

Thanks to their lightness and versatility combined with excellent mechanical properties, composite materials underwent an increasing relevance in the last twenty years in many industrial fields, also for structural applications. This class of materials offer a wide range of advantages but it is still characterized by a quite high cost with respect to more traditional structural materials. One of the reasons is the lack of reliable design procedures, as well as of extensive experimental investigations in the literature providing clear and general information. This is particularly evident with reference to the behaviour of composite laminates and bonded joints under multiaxial fatigue loading, which often characterise in-service conditions. With the aim to acquire information on the multiaxial fatigue behaviour of unidirectional composites, a specimen configuration was first defined, suitable to characterise the matrix-dominated multiaxial fatigue behaviour of a composite lamina, which is of great importance for the damage evolution in laminates (chapter 2). Tubular specimens subjected to combined tension/torsion loading were identified as the best compromise between reliability of results, easiness of testing and possibility to obtain multiaxial stress states of interest. In the third chapter the results of an extensive experimental investigation on tubular specimens is presented. Tubes were fatigue tested with several values of the biaxiality (shear to transverse) ratio and load ratio (ratio between the minimum and the maximum fatigue loads). A strong influence of both parameters was found on the off-axis crack initiation and propagation phenomena, as well as on the damage mechanisms at the micro-scale. Uniaxial fatigue tests were then carried out on multidirectional flat laminates, designed to achieve local multiaxial stress states similar to those applied to the tubes by means of tension/torsion external loads. This activity, presented in the fourth chapter, revealed the equivalence between external (obtained by applying external loads in different directions) and internal (due to material anisotropy) multiaxial stress states. This represents a fundamental step for the extension of experimental results and predictive models to general loading conditions. The experimental activity on tubes provided information on the damage mechanisms at the micro-scale, responsible for fatigue failure of a unidirectional lamina. On the basis of these mechanisms a criterion for predicting crack initiation in a unidirectional lamina under multiaxial fatigue was developed by means of a multiscale approach (chapter 5). This criterion resulted in sound agreement with the new data on tubes, with data on flat unidirectional laminates from the literature and with crack initiation data on the off-axis layers of the laminates reported in chapter 4. A basic topic related to the analysis of multidirectional laminates is the stiffness degradation due to off-axis cracks in their plies. Dealing with such a topic, an analytical model was developed for predicting the stiffness of a laminate as a function of the crack density in its layers accounting for the interaction between cracks in different layers (chapter 6). In addition the model is capable of calculating the stress re-distribution due to the presence of cracks. This is fundamental for the development of a new procedure for predicting the fatigue crack density evolution in multidirectional laminates, presented in chapter 7. To this aim the experimental observations, the analytical models and criteria previously presented, combined with a statistical approach, have been used to predict the initiation and propagation of multiple cracks in a laminate. As a consequence, when this procedure is combined with the model presented in chapter 6, both the stiffness degradation and the stress re-distribution, useful for the estimation of the total fatigue life, can be predicted. When composite laminates are used as adherends in bonded joints the bonding surface represents a critical position for the onset of fatigue cracks. As a consequence an experimental investigation on the propagation of a bondline crack in composite bonded joints subjected to mixed mode I + II (opening + sliding) fatigue loading was carried out and presented in chapter 8. A criterion to predict the crack propagation rate under mixed mode loading was also developed, based on the damage mechanisms observed during the experimental campaign. Eventually, in Appendix A an analytical model for predicting the initiation of a fibre-matrix debond crack under biaxial static loads is presented. The model provides useful information on the influence of the main geometrical and interface parameters of the fibre-matrix interface strength.
Grazie alla loro leggerezza e versatilità combinate ad eccellenti proprietà meccaniche, i materiali compositi hanno acquisito un'importanza sempre maggiore negli ultimi vent'anni in molti settori industriali, anche per applicazioni strutturali. A fronte dei numerosi vantaggi offerti da questa classe di materiali vi è un costo che rimane ancora piuttosto elevato rispetto ai più tradizionali materiali da costruzione. Una delle ragioni è la mancanza di procedure di progettazione affidabili e riconosciute, nonché l'assenza, in letteratura, di estese caratterizzazioni sperimentali da cui acquisire informazioni di carattere generale. Ciò è particolarmente evidente in riferimento al comportamento a fatica multiassiale di lamine, laminati e giunzioni incollate in composito. Al fine di sopperire alla mancanza di informazioni sul comportamento a fatica multiassiale di lamine unidirezionali, nonché all'assenza di una procedura adeguata di test, è stata inizialmente definita una configurazione di provini adatta a caratterizzare la risposta matrix-dominated (particolarmente significativa per il danneggiamento a fatica di laminati) di materiali compositi unidirezionali (capitolo 2). Provini tubolari soggetti a carichi ciclici di trazione e torsione combinati sono stati identificati come il miglior compromesso tra affidabilità dei risultati, semplicità di testing e possibilità di ottenere condizioni multiassiali di interesse. Nel terzo capitolo sono riportati i risultati di un'estesa campagna sperimentale su tali provini tubolari in presenza di diversi rapporti di biassialità (tensione di taglio su tensione trasversale) e rapporti di ciclo (rapporto tra il minimo e il massimo carico di fatica). É stata riscontrata una notevole influenza di tali parametri sull'innesco e propagazione di cricche off-axis, nonché sui meccanismi di danneggiamento su scala microscopica. Sono poi stati testati a fatica uni-assiale dei laminai piani multi-direzionali progettati per avere condizioni di multiassialità locali simili a quelle ottenute sui provini tubolari tramite carichi esterni in diverse direzioni. L'attività, presentata al quarto capitolo, ha permesso di verificare l'equivalenza tra condizioni multiassiali ti tipo esterno (carichi in più direzioni) e interno (dovute all'anisotropia di lamine e laminati in composito). Ciò rappresenta uno step fondamentale per l'estensione di risultati sperimentali e modelli previsionali a condizioni di carico generiche. L'attività sperimentale sviluppata sui tubi ha fornito informazioni sui meccanismi di danneggiamento a livello microscopico che sono responsabili del cedimento a fatica della lamina unidirezionale. Sulla base di tali meccanismi è stato proposto un criterio per l'innesco di cricche a fatica multiassiale in lamine in composito basato su un approccio multiscala (capitolo 5). Il criterio è risultato in ottimo accordo con i nuovi dati sperimentali sui campioni tubolari, con dati disponibili in letteratura riguardanti lamine unidirezionali piane e con i dati ad innesco sugli strati off-axis dei laminati testati al capitolo 4. Parlando quindi di laminati multi-direzionali, un aspetto fondamentale è la diminuzione di rigidezza di questi ultimi dovuto all'innesco e propagazione di cricche multiple negli strati off-axis. A tal proposito è stato proposto un modello analitico in grado di legare la densità di cricche in ciascuno strato di un laminato alla diminuzione di rigidezza globale considerando anche l'interazione tra cricche presenti su strati diversi (capitolo 6). Tale modello fornisce anche le distribuzioni di tensione dovute alla presenza delle cricche stesse. Questo è un aspetto di fondamentale importanza per lo sviluppo di una procedura per prevedere l'evoluzione della densità di cricche in laminati multi-direzionali sollecitati a fatica, presentata al capitolo 7. A tale scopo le osservazioni sperimentali, i modelli analitici e i criteri sviluppati in precedenza, combinati ad un approccio di tipo statistico, vengono utilizzati per prevedere l'innesco e propagazione di cricche multiple in un laminato. Di conseguenza, combinata con il modello precedentemente illustrato, la procedura consente di prevedere sia la diminuzione di rigidezza di laminati sia la ridistribuzione delle tensioni per effetto del danneggiamento rappresentando quindi uno strumento utile anche alla stima della vita a fatica totale di un laminato. Quando i laminati in composito sono utilizzati come aderendi in giunzioni incollate, l'interfaccia di incollaggio rappresenta una zona particolarmente critica per l'innesco di cricche a fatica. Di conseguenza è stata analizzata sperimentalmente la propagazione di cricche in giunzioni incollate soggette a carichi ciclici di modo misto I + II (apertura + scorrimento). Ancora una volta i meccanismi osservati su scala microscopica sono stati utilizzati per la formulazione di un criterio damage-based per la previsione della velocità di propagazione di cricche in giunzioni incollate sollecitate in modo misto (capitolo 8). In fine, in Appendice A è presentato un modello analitico sviluppato per la previsione dell'innesco di una cricca di debonding tra fibra e matrice in condizioni di carico statico biassiale. Il modello è utile per trarre informazioni sull'influenza dei principali parametri geometrici e interfacciali sulla resistenza dell'interfaccia fibra-matrice.

Les travaux présentés ont consisté à développer des stratégies d'identification performantes des paramètres des lois de comportement superélastique des Alliages à Mémoire de Forme (AMF). L'objectif est de disposer d'une solution complète de caractérisation, d'identification, et de simulation de structures en AMF soumises à des sollicitations complexes. Une base de données expérimentale unifiée pour un alliage de NiTi superélastique a été établie pour une multitude de trajets de déformation multiaxiaux et à différentes températures : en traction homogène, en compression, en traction-compression et en traction-traction. Une caractérisation expérimentale a été développée sur une plate-forme multiaxiale assemblée au laboratoire durant ce travail. L'emploi de la corrélation d'images a permis d'enrichir la base de données expérimentale en déterminant pour chaque essai les champs cinématiques. Cette collection d'essais a permis de montrer l'importante différence de comportement observée entre les directions de laminage et transverse, bien que le matériau soit faiblement texturé. Des procédures d'identification du comportement thermomécanique des AMF ont été mises en place, basées sur la construction et minimisation d'une fonction objectif régularisée. La première est basée sur l'exploitation des courbes contrainte-déformation moyennes sous chargement homogène et unixial. La seconde exploite la richesse des champs de déformations mesurés en essai hétérogène. Les deux stratégies ont permis d'identifier les huit paramètres gouvernant le comportement superélastique du modèle de Chemisky et al. (Chemisky et al. 2011). Des différences entre les jeux de paramètres identifiés sont caractéristiques des effets d'anisotropie observés. Le succès de cette stratégie démontre sa pertinence et est encourageant pour l'identification de paramètres de lois de comportement anisotropes
In this work, efficient identification strategies were developed to determine the characteristic parameters of the thermomechanical behavior of pseudoelastic Shape Memory Alloys (SMA). The aim is to obtain a complete solution for characterization, identification and numerical simulation of SMA structures undergoing multiaxial loading paths. A unified experimental database has been constructed to characterize the behavior of superelastic NiTi SMAs. This database includes tension, compression, tension-tension and tension-compression multiaxial tests at different temperatures. A characterization methodology has been developed on a multiaxial testing setup, which has been assembled in the laboratory during this Ph.D. project. Vital information about the strain fields for each test is added to the experimental database through the use of Digital Image Correlation. A significant difference in the thermomechanical behavior between the rolling and transverse directions has been observed, even when the specimens are not strongly textured. Two strategies were developed that rely on the minimization of a regularized cost function for identification of thermomechanical constitutive law parameters. The first identification procedure is based on uniaxial homogeneous tests at different temperatures. In the other strategy the information of strain fields of heterogeneous tests are utilized. In each case, the eight material parameters of the constitutive law of Chemisky et al. (Chemisky et al. 2011) have been identified. A difference between the identified parameters in the rolling and transverse direction is noted and corresponds to the effect of anisotropy. Nevertheless, the capabilities of the relevant identification strategies shall allow the determination of the parameters of anisotropic constitutive laws

Ce travail est consacre a l'elaboration d'une methode de calcul de la duree de vie a l'amorcage applicable au cas de la fatigue multiaxiale a grand nombre de cycles des metaux polycristallins. Tout au long de l'etude, un soin particulier est apporte a la description de l'influence du dephasage sur l'accumulation du dommage. Au cours d'une analyse bibliographique, differents criteres d'endurance et quelques methodes de calcul de la duree de vie concernant les chargements d'amplitude variable sont decrits. Les propositions issues de l'approche microscopique sont analysees en detail. Pour etablir la nouvelle methode, la deformation plastique microscopique accumulee est choisie comme variable de dommage. Son calcul necessite le reperage du plan subissant le plus grand dommage. Apres la presentation des etapes du calcul dans le cas des chargements multiaxiaux sinusoidaux et une confrontation encourageante avec des resultats experimentaux, la methode est etendue aux chargements multiaxiaux quelconques. Une nouvelle procedure d'equivalence destinee au controle de la tenue en fatigue des structures est proposee. Finalement, des essais sous chargement d'amplitude variable sont entrepris afin de valider experimentalement la methode presentee. Le materiau teste est un acier a haute resistance de type 35ncd16 et le chargement applique est une sequence standard automobile (carlos). Pour trois types de sollicitation (traction, torsion et traction-torsion), on constate que les previsions du modele sont en bon accord avec les durees de vie experimentales

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2018.
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A presente dissertação avalia três métodos para cálculo da amplitude de tensão cisalhante equivalente utilizada em modelos de fadiga multiaxial baseados na abordagem do plano crítico. Avaliou-se o Método da Mínima Circunferência Circunscrita (MCC), o Método da Caixa (MRH) e o Método do Momento de Inércia (MOI). Com os resultados desses métodos foram aplicados três critérios de fadiga multiaxial: o critério de Susmel e Lazzarin (2002), o critério de Findley (1956) e o critério de Matake (1977). O objetivo foi a avaliação de quais métodos aplicados aos critérios resultam em melhores estimativas de resistência à fadiga multiaxial. Para a validação da análise, foram utilizados dados disponíveis na literatura para espécimes fabricados em ligas de aço submetidos a carregamentos combinados de flexão e torção em iminência de falha por fadiga. Um Índice de Erro (IE), que fornece uma medida da distância entre a previsão dos modelos e os dados experimentais foi utilizado como medida da acurácia nesta análise. Conclui-se que, em um contexto geral, para os dados sob carregamentos síncronos em fase ou fora de fase, os melhores resultados foram obtidos pelo Método MRH aplicado conjuntamente com o modelo de Findley (1956) e, para os dados sob assíncronos, as melhores estimativas foram obtidas quando o MRH foi utilizado juntamente com o modelo de Susmel e Lazzarin (2002).
This thesis evaluate three different methods that calculate the equivalent shear stress amplitude using Multiaxial Fatigue models based on the Critical Plane approach. It was evaluated the Minimum Circumscribed Circle (MCC), the Maximum Rectangular Hull (MRH) and the Moment of Inertia (MOI). With the result of these methods on hands, it was applied three multiaxial fatigue criteria: Susmel and Lazzarin (2002), the Findley (1956) criteria and the Matake (1977) criteria. The aim of this was to evaluate which of these methods applied in these criteria result in the closest estimated of multiaxial fatigue resistance. In order to validate the analysis, it was used available data base to different types of steel loaded to combined torsion and bending at the limit of fatigue failure. In this way, a percentual error index was used to measure how distant the prediction of the criteria was to the empirical result. Therefore, it was showed that the best results were obtained by using the MRH method when applied to the Findley criteria for synchronous loadings and, for asynchronous loadings, the same method using the Susmel and Lazzarin (2002).

A associação entre epilepsia e transtornos psicóticos é amplamente relatada na literatura. Características clínicas e do seu impacto, tais como suicídio, tentativas de suicídio, homicídio e alterações cognitivas são evidenciados em poucos estudos que associam epilepsia e psicose. Este estudo comparou o impacto clínico e funcionamento psicossocial dos pacientes com epilepsia e transtornos psicóticos, analisando ainda as diferenças entre pacientes com psicose interictal e pós-ictal. O estudo consiste de uma revisão de prontuário de todos os pacientes atendidos no PRONEPSI com epilepsia e transtornos mentais. Foram estudados 143 indivíduos, divididos em dois grupos: 82 pacientes com diagnóstico de epilepsia e transtornos psicóticos e 61 pacientes com epilepsia e outro transtorno mental. O grupo de pacientes psicóticos foi estudado comparando dados entre pacientes com psicose interictal (53) e pós-ictal (17). O grupo de pacientes com transtornos psicóticos apresentou menor escolaridade, mais história familiar de psicose, maior número de tentativas de homicídio, mais estados de mal epiléptico, mais internações psiquiátricas, história pregressa de insulto ao SNC e retardo mental. Além disso, a epilepsia foi considerada um fator causal importante para desenvolvimento da psicose. O grupo de pacientes com transtornos psicóticos também se diferenciou, revelando maior impacto na esfera cognitiva, vocacional e pessoal. Os pacientes com psicose interictal tiveram mais história familiar para psicose e a epilepsia foi considerada um fator causal importante para seu desenvolvimento. Pacientes com epilepsia e transtornos psicóticos apresentam um maior comprometimento clínico geral o que interfere diretamente no seu comprometimento funcional e na gravidade do impacto. Os pacientes com epilepsias mais graves e algum tipo de insulto ao SNC parecem ser mais vulneráveis ao desenvolvimento de transtornos psicóticos em comparação aos pacientes com formas menos graves de epilepsia
The association between epilepsy and psychotic disorders has been well documented in literature. Although this association is well-known, few studies regarding psychosis and epilepsy investigated the clinical characteristics of these patients and its impact on psychosocial function, suicide and suicide attempts, homicide attempts and cognitive deficits. The aim of this chart review was to compare the clinical impact and the psychosocial function between patients with epilepsy and psychotic disorders and patients with epilepsy and other psychiatric disorders. We also compared the clinical characteristics and psychosocial function between patients with postictal psychosis and interictal psychosis. We reviewed 143 charts, divided in two groups: 82 charts of patients with epilepsy and psychotic disorders and 61 charts of patients with epilepsy and other psychiatric disorders. In the group of patients with epilepsy and psychosis, 53 had a diagnosis of interictal psychosis and 17 of postictal psychosis. Patients with psychotic disorders had fewer years of education, more family history of psychotic disorders and higher number of homicide attempts, status epilepticus, psychiatric admissions and history of central nervous system insults. They also presented more impact on cognitive, vocational and interpersonal scales. Epilepsy was considered a major cause to the development of psychosis. Regarding the differences between patients with interictal and postictal psychosis, the only difference found was that the patients with interictal psychosis presented more family history of psychosis. Also, in both groups epilepsy was considered a major cause to the development of psychosis. Patients with psychotic disorders had a more severe clinical impairment in comparison with patients with other psychiatric disorders, which may have interfered in psychosocial functioning and severity of impact. Patients with central nervous system\'s insults and severe epilepsy may be likely more prone to psychosis\'s development than other patients with less severe forms of epilepsy

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The evolution of techniques for the development of equipment capable of translating the results taken from a diverse and complex set of tasks carried out by the human body, has become an important item on the scientific communities agenda. Within the context of such equipment, the force plate has shown itself capable of being implemented for the task of measuring phenomena, which before could only be observed visually. This work has as its objective to describe and develop an extensometric, multiaxial force plate, for use as a biomedical assistance apparatus. Sensors for the detection of forces such as strain gauges were used and fixed in predetermined areas on the four transducers, which are an integral and fundamental part of the force plate apparatus. The cell design was completed using geometry capable of coupling with the minimum of interference the two different forces present within the structure. In this manner it is possible to quantify the forces in three orthogonal directions. The prototype developed can be utilized, for example as an evaluation tool for both gait and stability research. In parallel to the development of the force plate, equipment for carrying out the conditioning and digitalization of signals originating from the load cells was designed and constructed. The control of the acquisition processes as well as the processing of signals received from the force plate is carried out by the use of a specific applicative, which makes the quantitative values of the forces, strength and momentum available, allowing for the calculation of the parameters used for the respective biomedical evaluations, especially those dealing with the oscillation of the human body in an erect near static posture. Still further the applicative provides a confidence ellipse obtained from the stability evaluations carried out along with the coordinates of pressure center and standard stability indexes obtained instantaneously.
A evolução das técnicas para desenvolver equipamentos capazes de traduzir o resultado de diversas tarefas complexas exercidas pelo corpo humano, tornou-se evidente para a comunidade científica. Dentre esses equipamentos, a plataforma de força mostrou ser uma ferramenta capaz de ser empregada para a mensuração de fenômenos antes só observados. Este trabalho tem por objetivo descrever o projeto e o desenvolvimento de uma plataforma de força extensométrica, multiaxial, para uso em instrumentação biomédica. Sensores para detecção de esforços, do tipo strain gauge, foram utlizados e fixados em regiões previamente determinadas nos quatro transdutores que compõem o conjunto da plataforma. O projeto das células considera uma geometria capaz de desacoplar, com mínima interferência, dois esforços diferentes, presentes na mesma estrutura. Assim, pode-se quantizar esforços em três direções ortogonais. O protótipo desenvolvido pode ser utilizado como ferramenta para avaliações de marcha e estabilidade, por exemplo. Paralelamente ao desenvolvimento da plataforma, um equipamento para realizar o condicionamento e digitalização dos sinais provenientes das células de carga foi projetado e construído. O controle dos processos de aquisição e processamento dos sinais advindos da plataforma de força é realizado através de um aplicativo específico que disponibiliza os valores quantitativos dos esforços de força e momento, os quais permitem o cálculo de parâmetros relevantes às avaliações biomédicas, particularmente em avaliações a cerca da oscilação do corpo humano na postura ereta quasi-estática. O aplicativo fornece ainda as elipses de confiança obtidas a partir das avaliações de estabilidade realizadas, juntamente com as coordenadas do centro de pressão e índices de estabilidade padrão e instantâneos obtidos.
Mestre em Ciências

Literature concerning the development of mechanistic and empirical models of creep deformation and failure, under uniaxial and multiaxial stress systems are reviewed. The detailed metallurgy of the alloy is discussed and its specific creep behaviour in the experimental temperature range is reviewed from published experimental data, mostly obtained from the Alloy 800 Data Bank of the EEC Joint Research Centre at Petten.

Une géométrie d'éprouvette tubulaire de traction-torsion entaillée a été optimisée pour caractériser l'effet de l'état des contraintes (triaxialité et paramètre de Lode) sur la ductilité des métaux à faible taux de triaxialité. Des essais biaxiaux proportionnels ou non, accompagnés de mesures des champs cinématiques par stéréo-corrélation d'images ont été réalisés sur un acier 36NiCrMo16 revenu et un alliage d'aluminium 2024-T351. Les trajets de chargement à rupture (évolution au point critique de la déformation plastique équivalente, de la triaxialité des contraintes et du paramètre de Lode) ont été obtenus. L'évolution de la ductilité de l'alliage d'aluminium en fonction de la triaxialité obtenue en traction-torsion diffère notablement de celle obtenue par Bao et Wierbicki en 2004 qui suggérait une ductilité minimale en cisaillement, tandis que la technique de traction-torsion révèle une ductilité maximale en cisaillement. Un effet notable des trajets de chargement non monotones ou non proportionnels sur la ductilité a été mis en évidence au moyen d'essais séquentiels composés d'un pré-chargement en compression, torsion ou traction, suivi d'une séquence de chargement proportionnel en traction-torsion combinées. Des observations au MEB de coupes métallographiques à l'issue d'essais biaxiaux interrompus, ainsi qu'un suivi en temps réel de la déformation et de l'endommagement en surface, lors d'essais de torsion dans le MEB et un essai de fissuration couplé à un suivi 3D de l'endommagement par laminographie sous rayonnement synchrotron ont mis en évidence des phénomènes de localisation à de multiples échelles ainsi que la croissance de certaines cavités, même en cisaillement pur, qui contraste avec l'affaissement total prédit par les modèles de cellule élémentaire. Ceci semble lié à l'allongement axial significatif mesuré en torsion pure (effet Swift). La localisation par cisaillement apparaît comme le mécanisme prédominant de coalescence des cavités, ce qui justifie l'adoption d'un critère d'initiation de la rupture de type Hosford-Coulomb. Utilisé en conjonction avec un indicateur non-linéaire d'endommagement il permet de rendre compte des ductilités mesurées, y compris sous chargement potentiellement non-proportionnel
A stocky tubular tension-torsion specimen geometry was optimized to characterize the effect of the stress state (stress triaxiality and Lode angle parameter) on metals ductility, at low stress triaxialities. Biaxial tests (proportional and non-proportional) were performed on 36NiCrMo16 steel and 2024-T351 aluminum alloy. Strain fields were measured by stereo-correlation of digital images during the tests. Loading paths to fracture (evolution of the equivalent plastic strain, the stress triaxiality and the Lode angle parameter at the critical point) were determined. The evolution of aluminum ductility with respect to the stress triaxiality measured from tension-torsion tests differed substantially from that obtained by Bao and Wierzbicki in 2004. Indeed, the latter suggested a minimal ductility under shear, while the tension-torsion technique revealed a maximal ductility under shear. Non-proportional loading paths were shown to have an influence on ductility, by means of tests consisting in a pre-compression, pre-tension or pre-torsion, followed by a proportional loading sequence under combined tension-torsion. SEM observations of metallographic sections from biaxial interrupted tests, a real-time monitoring of the surface strain and damage during in-situ torsion tests in the SEM, and a crack propagation test coupled with in-situ X-ray synchrotron laminography brought evidences of localization phenomena at different scales, and of the growth of some cavities, even under pure shear, by contrast with the total collapse predicted by unit cell models. This growth may be due to the significant axial elongation measured under pure torsion (Swift effect). Shear localization was identified as the main coalescence mechanism, which justifies the choice of the Hosford-Coulomb fracture initiation criterion. Used in conjunction with a non-linear damage indicator, it accounts for the measured ductilities, even under possibly non-proportional loadings