Pour améliorer la caractérisation et le dimensionnement des disques de turbines pour les moteurs d’avion, le motoriste Safran Aircraft Engines (SAE) développe des modèles de comportement, des lois d’endommagement et des critères de fatigue plus adaptés aux chargements réels. Pour aider à cette démarche, le but de cette étude est de développer un modèle de plasticité adapté à l'Inco718DA (un alliage à base nickel utilisé dans la fabrication des turbines haute pression), capable de représenter différents chargements (monotone, cyclique symétrique et non-symétrique). La proposition puis l'identification du modèle a été possible grâce à une campagne expérimentale favorisant des tests complexes et innovants aux essais de fatigue nombreux et coûteux. Les essais faits incluent un essai monotone avec décharges élastiques, un essai multi-niveau à Rε=-1 et deux essais multi-niveau à Rε=0 pour mieux caractériser la relaxation de la contrainte moyenne et un essai pour quantifer le rochet. Le comportement cyclique du matériau a été identifié en utilisant un écrouissage cinématique non saturant avec des éléments s'inspirant de la surface mémoire de Chaboche. Un des défis a été d'obtenir des boucles stabilisées "pointues" dans un régime de plasticité cyclique saturante, en utilisant une évolution du paramètre Γ en fonction de la déformation plastique équivalente maximale (prefacteur du terme de rappel de la loi d'écrouissage cinématique).Une deuxième difficulté apparaît dans la description de la relaxation de la contrainte moyenne, phénomène complexe avec un impact considérable sur la durée de vie en fatigue. Dans le chapitre 3, un modèle est proposé pour la caractérisation de la relaxation partielle de la contrainte moyenne. Une originalité du modèle est l'idée que la relaxation incomplète est une conséquence directe de la différence entre la charge et la décharge de la boucle de hystérésis. Le paramètre choisi pour décrire cette différence a été le préfacteur du terme de rappel Γ, pour lequel la thermodynamique donne de la liberté. Par rapport à d'autres lois d'écrouissage confirmées, notre modèle présente l'avantage d'utiliser un seul terme de rappel, mais avec une formulation plus complexe. En plus, le modèle est incrémental (écrit en taux/en vitesse), il peut donc prendre en compte des chargements complexes tels que aléatoires ou plus simplement tels que dans les essais multi-niveaux pilotés en déformation. Dans le dernier chapitre de la thèse, une campagne biaxiale vaste est présentée, avec les développements pour réaliser des essais biaxiaux pilotés en déformation. La campagne biaxiale a été réalisée sur des éprouvettes cruciformes en utilisant des capteurs LASER et des mesures de champs mono et stéréo analysées en utilisant la Corrélation d'Images Numeriques (CIN). Pour analyser la relaxation de la contrainte moyenne en biaxial un moyen de mesure et de contrôle fiable a dû être développé, adapté aux déformations plastiques élevées qui apparaissent dans la région d'intérêt de l'éprouvette. En utilisant la corrélation d'images intégrée (I-CIN) avec des fonctions de forme adaptées sur un seul élément et des calculs sur GPU, on a obtenu des fréquences de mesure de 100~Hz. En plus, avec sa précision et vitesse, I-CIN a été une technique adaptée pour contrôler une machine d'essais multiaxiale hydraulique. Un résultat important obtenu quand on a réalisé des essais equi-biaxiaux pilotés en déformation a été l'observation d'une relaxation de la contrainte moyenne très faible par rapport au cas uniaxial. Ce résultat doit être pris en compte dans les études futures avec des calculs éléments finis sur l'éprouvette complète. / To improve the characterization and design of aircraft engine turbine disks, the propulsion systems manufacturer Safran Aircraft Engines (SAE) develops constitutive equations, damage laws and fatigue criteria that are more adapted to real loadings. As part of this effort, the purpose of the current study is to develop a plasticity model for Inco718DA (a nickel-based alloy used in the manufacturing of high-pressure turbine disks), capable of representing several loading conditions (monotonic, symmetrical and non-symmetrical cyclic loading). The identification of the model was possible thanks to a uniaxial campaign, favoring a few but complex, innovative, tests to numerous costly fatigue tests. The tests we performed include a monotonic test with elastic discharges, a multi-level Rε = -1 test and two multi-level Rε = 0 tests that better quantify the mean stress relaxation and a test to identify ratcheting. The cyclic behavior was identified using a non-saturating kinematic hardening law with elements of Chaboche's memory surface. One of the challenges was to obtain sharp stabilized loops in a saturated cyclic plasticity regime, which was possible using parameter Γ evolving with respect to the maximum equivalent plastic strain, in the back-stress of kinematic hardening rule.A second difficulty appears in the description of mean stress relaxation, which has a considerable impact on fatigue lifetime. In chapter 3, a model is proposed for the description of the incomplete mean stress relaxation. One of the originalities is the idea that incomplete mean stress relaxation is a direct consequence of the difference between the loading and the unloading part of the hysteresis loop. The parameter we used to describe this difference, was the prefactor of the back-stress term Γ, for which the thermodynamics allows liberty. When compared to confirmed kinematic hardening laws that model non-zero mean stress relaxation, our model presents the advantage of using only one backstress, even if its description is more complex. Moreover, the model is incremental (written in a rate form in chapter 3 section 5) so it can take into account complex loadings such as multi-level strain-controlled tests.In the last chapter of the thesis, a vast biaxial campaign is presented, along with developments to make biaxial strain-controlled tests. The biaxial campaign was performed on cross-shaped samples using LASER sensors, mono and stereo full-field measurements using Digital Image Correlation (DIC). In order to analyze biaxial mean stress relaxation, a reliable measurement and control method had to be developed for the high plastic strains occurring in the region of interest of the sample. By using an Integrated-DIC (I-DIC) algorithm with adequate shape functions on one element and GPU computations we were able to obtain measurement frequencies of 100 Hz. Moreover, with its precision and speed, I-DIC proved to be a suitable technique for controlling a biaxial hydraulic machine. An important result obtained when performing equi-biaxial I-DIC strain-controlled tests was that there was very little biaxial mean stress relaxation, with respect to the uniaxial case. This result will have to be taken into account in future studies when performing finite element computations of the whole sample.

M.A. / Violence being a prominent and invasive factor in South Africa has left many people feeling powerless, hopeless and incapable of dealing and coping with the effects that exposure to trauma has produced. This idea appears even more disturbing if one considers that military personnel will inevitably be exposed to some form of trauma in their employment history. As a result of this traumatic exposure, many people develop post traumatic stress disorder or symptoms thereof. The literature ind icates that certain variables may increase vulnerability for the development of this disorder. The purpose of this research was to evaluate whether or not there is a relationship between Post Traumatic Stress (PTS) symptoms and axis II personality traits using Millon’s Clinical Multiaxial Inventory (MCMI - III) as a measure. The results of which will have major implications for our understanding of PTS, as well as aid in the deployment of military personnel. The sample comprised 5853 military personnel who completed the MCMI III as part of a yearly project to determine their mental health status. Inferential and descriptive statistical analyses were used on the data. It was found, in accordance with previous literature findings, that narcissistic, antisocial and borderline personality styles are the best predictors of PTS. In addition, the study found that there is a significant relationship between PTS and various personality styles, namely depressive, schizotypal, borderline, passive -aggressive, compulsive, antisocial and narcissistic personality styles. It is recommended that if the MCMI-III is used to scan military personnel prior to combat, those with high scores on borderline, narcissistic and antisocial personality scales, should be subjected to a more in-depth evaluation.

La presente investigación tuvo como objetivo determinar la validez de constructo y la eficiencia diagnóstica de las escalas Depresión Mayor y Trastorno de Ansiedad del Inventario Clínico Multiaxial de Millon-III (MCMI-III). Para ello, se aplicó el MCMI-III, el Inventario de Depresión de Beck y el Inventario de Ansiedad de Beck a 100 pacientes ambulatorios de un hospital de salud mental de Lima Metropolitana. La muestra estuvo conformada por 68 mujeres y 32 hombres, cuyas edades fluctúan entre los 18 y 56 años (M=30.53; DE=10.11). Al calcularse la validez de constructo, se encontró que las escalas del MCMI-III presentaban correlaciones convergentes con las otras medidas de depresión y ansiedad utilizadas; sin embargo, también mostraban una pobre habilidad para discriminar la sintomatología del trastorno que dicen medir y la de otra patología considerada en esta investigación. Asimismo, al calcular los criterios que sustentan la efectividad diagnóstica (sensibilidad, especificidad, poder predictivo positivo y poder predictivo negativo) para cada escala, se obtuvo que la escala Trastorno de Ansiedad presenta una mayor eficacia diagnóstica que la escala Depresión Mayor. No obstante, la escala Trastorno de Ansiedad brinda un porcentaje alto de falsos positivos; mientras que la escala Depresión Mayor brinda falsos negativos. / Tesis

L'industrie automobile utilise de nombreuses pièces en caoutchouc aux fonctions antivibratoires, dont il faut garantir la tenue en service. L'objectif de ce travail de thèse est de proposer une méthode pour prévoir la durée de vie en fatigue d'une structure en caoutchouc naturel chargé au noir de carbone. La démarche proposée consiste à découpler l'évolution du comportement mécanique et l'endommagement sous chargement cyclique. On suppose qu'il existe un cycle stabilisé et que la durée de vie, définie comme l'amorçage d'une fissure détectable, ne dépend que des grandeurs mécaniques évaluées sur celui-ci. Les élastomères soumis à un chargement cyclique présentent un adoucissement associé à l'effet Mullins, qui se produit surtout pendant les premiers cycles, après lesquels la réponse du matériau reste identique. On propose un modèle capable de décrire cette réponse stabilisée, ne dépendant que des variables mécaniques en régime établi. Ses paramètres sont les élongations maximales dans un nombre fini de directions matérielles, de façon à décrire l'anisotropie induite par l'effet Mullins. Ce modèle est ensuite utilisé pour analyser un grand nombre d'essais d'endurance uniaxiaux et multiaxiaux, réalisés sur éprouvettes axisymétriques. On montre qu'il permet de prendre en compte efficacement l'influence du type de contrôle ou d'une précharge. L'analyse des essais multiaxiaux ne mettant pas en jeu de renforcement, c'est-à-dire passant par l'état de déformation nul, montre que la contrainte principale maximale est suffisante pour représenter tous les cas de chargement, à l'exception de ceux qui font intervenir des phénomènes de cumul multi-plans. On propose alors une loi de cumul d'endommagement pour représenter ce type de chargement.

Les structures sandwichs dissymétriques sont un cas particulier de la famille des structures sandwichs. Elles présentent une peau dite travaillante qui est chargée en membrane. Celle-ci est stabilisée par une âme en nid d'abeille Nomex et une contre-peau dite peau stabilisatrice. Cette configuration génère un comportement non linéaire géométrique. Plusieurs thèories analytiques des poutres et plaques sandwichs dissymétriques ont été élaborées basées sur le minimum de l'énergie potentielle ou le principe des puissances virtuelles associées à une méthode de discrétisation de Ritz. Ces théories intégrent de plus la modélisation a priori ou a posteriori de la compression de l'âme. Parallélement un montage d'essai sous sollicitations combinées compression/cisaillement a été développé et des essais multiaxiaux ont été réalisés sur éprouvettes neuves et impactées. Une comparaison théorie/expérience est aussi réalisée.

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2018. / Submitted by Raquel Almeida (raquel.df13@gmail.com) on 2018-05-07T18:41:32Z No. of bitstreams: 1 2018_CainãBemficadeBarros.pdf: 12251436 bytes, checksum: 876fa05cf00aed82da7e296be39eec5e (MD5) / Approved for entry into archive by Raquel Viana (raquelviana@bce.unb.br) on 2018-05-23T11:34:13Z (GMT) No. of bitstreams: 1 2018_CainãBemficadeBarros.pdf: 12251436 bytes, checksum: 876fa05cf00aed82da7e296be39eec5e (MD5) / Made available in DSpace on 2018-05-23T11:34:13Z (GMT). No. of bitstreams: 1 2018_CainãBemficadeBarros.pdf: 12251436 bytes, checksum: 876fa05cf00aed82da7e296be39eec5e (MD5) Previous issue date: 2018-05-23 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). / Os objetivos deste trabalho são investigar o comportamento tensão-deformação cíclico e a fadiga multiaxial do aço inoxidável 304L por meio de ensaios axiais, torsionais e axiais-torsionais proporcionais totalmente alternados controlados por deformação à temperatura ambiente e avaliar os modelos de fadiga do tipo plano crítico propostos por Smith, Watson e Topper (1970), e Fatemi e Socie (1988) em relação à previsão de vida à fadiga e à orientação das trincas macroscópicas. Corpos de prova tubulares com paredes finas usinados após o tratamento térmico de normalização foram submetidos a amplitudes de deformação equivalente de von Mises tais que 0,20% ≤ Δ/2 ≤ 1,00%. Devido à dependência da taxa de carregamento do comportamento tensão deformação do aço inoxidável 304L, todos os ensaios foram realizados com frequências (0,30-2,00 Hz) tais que a taxa de deformação equivalente de von Mises fosse igual a 10-2 s-1. Observou-se que o endurecimento secundário nos ensaios proporcionais só ocorreu para amplitudes de deformação equivalente Δ/2 ≥ 0,80% enquanto todos os ensaios axiais-torsionais apresentaram endurecimento secundário. Baseado na comparação entre os estados de tensão, concluiu-se que há falha por fadiga antes que o endurecimento secundário se torne significativo para os ensaios proporcionais cuja Δ/2 ≤ 0,60%. Observou-se um comportamento do tipo Masing para uma faixa de deformação axial Δ/2 ≤ 0,40% e torsional Δ/2 ≤ 0,61% para ensaios axiais, torsionais e proporcionais. A deformação equivalente de von Mises não pode ser usada como parâmetro limite para o comportamento Masing já que o ensaio proporcional cuja Δ/2 = 0,50% apresenta comportamento semelhante àquele de ensaios cuja Δ/2 ≤0,50%, o que não ocorre para o ensaio axial de mesma amplitude de deformação equivalente. Observou-se não proporcionalidade nos espaços das tensões desviadoras e das deformações plásticas para os ensaios proporcionais no espaço das deformações totais. No entanto, não se observou um aumento na amplitude de tensão destes ensaios quando comparados a ensaios axiais e torsionais, o que sugere que o endurecimento não proporcional está associado à não proporcionalidade no espaço das deformações totais. Não houve influência significativa do endurecimento secundário na análise de fadiga, já que não houve diferença significativa entre as estimativas de vida realizadas com constantes materiais obtidas de diferentes ciclos de referência para os dois modelos. Os modelos investigados previram a vida à fadiga com boa acurária, mas falharam em prever a orientação das trincas para todas as três histórias de deformação. / The goals of this work are to investigate the cyclic stress-strain behaviour and the multiaxial fatigue of the 304L stainless steel through fully reversed strain-controlled axial, torsional and proportional axial-torsional experiments at room temperature and to evaluate the critical plane fatigue models proposed by Smith, Watson and Topper (1970), and Fatemi and Socie (1988) regarding the fatigue life and the macroscopic fatigue crack orientation. Thin-walled tubular specimens machined after a normalization heat treatment were submitted equivalent von Mises strain amplitudes such that 0:20% "eq=2 1:00%. Due to the rate-dependent cyclic stressstrain behaviour of the 304L stainless steel, all experiments were performed with frequencies (0.30{2.00 Hz) such that the equivalent von Mises strain rate was equal to 102 s1. It was observed that the secondary hardening upon proportional loads occurred only for "eq=2 0:80%, whilst it occurred for all axial and torsional experiments. Based upon the comparison between stress states, it was concluded that fatigue failure occurs before the secondary hardening becomes important for proportional experiments whose "eq=2 0:60%. A Masing-type behaviour was observed for a range of axial strain "=2 0:40% and torsional strain sur=2 0:61% for axial, torsional and proportional experiments. The equivalent von Mises strain amplitude cannot be used as a threshold since the proportional experiment whose "eq=2 = 0:50% exhibits a behaviour similar to experiments whose "eq=2 < 0:50%, which does not occur for the axial experiment with the same equivalent strain amplitude. non-proportionality upon deviatoric stress and plastic strain spaces was observed for proportional experiments upon total strain space. Nonetheless, an increase in stress amplitude was not observed for those experiments when compared to axial and torsional ones, which suggests that non-proportional hardening is related to non-proportionality upon the total strain space. There was no signi cant inuence of secondary hardening upon fatigue analysis since there was no signi cant di erence between life predictions generated from material constants obtained from di erent reference cycles for both models. The investigated models predicted accurately fatigue life, but failed to predict crack orientation for all the three strain histories.

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2017. / Submitted by Raiane Silva (raianesilva@bce.unb.br) on 2017-08-02T18:26:08Z No. of bitstreams: 1 2017_AllineChristineDinizZanette.pdf: 1602844 bytes, checksum: c0ea542c283a98ddc44ab50f02e97038 (MD5) / Approved for entry into archive by Raquel Viana (raquelviana@bce.unb.br) on 2017-09-11T21:41:34Z (GMT) No. of bitstreams: 1 2017_AllineChristineDinizZanette.pdf: 1602844 bytes, checksum: c0ea542c283a98ddc44ab50f02e97038 (MD5) / Made available in DSpace on 2017-09-11T21:41:35Z (GMT). No. of bitstreams: 1 2017_AllineChristineDinizZanette.pdf: 1602844 bytes, checksum: c0ea542c283a98ddc44ab50f02e97038 (MD5) Previous issue date: 2017-09-11 / Este trabalho apresenta um estudo e verificação do modelo de Jiang para estimativa de vida à fadiga no contexto de carregamentos multiaxiais para o aço 1045. Este modelo incorpora conceitos de plano crítico e energia, dispensando a utilização de métodos de contagem de ciclos para estimar a falha por fadiga. Foi utilizado o modelo de Chaboche para plasticidade cíclica para gerar histórias de tensão usadas nas simulações efetuadas. As trajetórias foram do tipo uniaxial totalmente reversa, torção pura, proporcional e elíptica não proporcional. Foram discutidos aspectos específicos do modelo de Jiang, bem como de seus parâmetros e dos resultados obtidos, tendo ele se mostrado satisfatório para produzir estimativas de vida à fadiga. / This works presents an analysis of the fatigue life estimation model proposed by Jiang as well as its verification under multiaxial loads for 1045 Steel. The Jiang model incorporates both critical plane and energy concepts, hence no cycle counting is needed to estimate fatigue life. The Chaboche cyclic plasticity model was adopted in order to generate the required loading history used in the simulations, whilst the loading paths herein used were: completely reversed uniaxial, pure torsional, proportional and non-proportional elliptical. A satisfactory verification was obtained, with results and analyses of the model and its parameters being later discussed.

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2016. / Submitted by Fernanda Percia França (fernandafranca@bce.unb.br) on 2016-08-23T18:18:32Z No. of bitstreams: 1 2016_JhonatandaPonteLópes.pdf: 8116037 bytes, checksum: f43347be866b7dc0775ad94de3dea587 (MD5) / Approved for entry into archive by Raquel Viana(raquelviana@bce.unb.br) on 2016-10-20T19:50:59Z (GMT) No. of bitstreams: 1 2016_JhonatandaPonteLópes.pdf: 8116037 bytes, checksum: f43347be866b7dc0775ad94de3dea587 (MD5) / Made available in DSpace on 2016-10-20T19:50:59Z (GMT). No. of bitstreams: 1 2016_JhonatandaPonteLópes.pdf: 8116037 bytes, checksum: f43347be866b7dc0775ad94de3dea587 (MD5) / Neste trabalho, busca-se utilizar o modelo de dano contínuo de Lemaitre como uma ferramenta de obtenção de vida em fadiga multiaxial para carregamentos proporcionais e não proporcionais. Primeiramente é apresentado o modelo matemático de Lemaitre, em que são formuladas as relações constitutivas necessárias à elaboração do modelo. O modelo de Chaboche foi escolhido para descrever a lei de evolução da tensão de endurecimento cinemático. Em seguida, é desenvolvido o modelo numérico para a solução das equações constitutivas, utilizando a lei de Chaboche com três termos e discretização implícita de Euler. Após, é feita a identificação dos parâmetros constitutivos do modelo para os aços 304 e S460N e para a liga de alumínio 6061-T6. É feita a implementação do modelo em uma rotina em linguagem FORTRAN, a qual é submetida a carregamentos uniaxiais e multiaxiais proporcionais e não proporcionais para cada material. Os dados de vida em fadiga obtidos pelo modelo de Lemaitre são, então, comparados com os dados experimentais disponíveis na literatura. É feita, em seguida, uma análise das amplitudes de tensão obtidas pelo modelo, as quais são comparadas com os dados experimentais. São obtidas, também, curvas de evolução do dano para cada carregamento e material. Os resultados obtidos mostram que o modelo de dano de Lemaitre descreve de maneira adequada o comportamento dos materiais analisados em fadiga de baixo ciclo, quando altas amplitudes de deformação são aplicadas. _________________________________________________________________________________________________ ABSTRACT / This project seeks to use Lemaitre’s Continuous Damage Model to obtain fatigue life estimates under multiaxial proportional and non-proportional loadings. Initially, the Lemaitre’s mathematical model is presented, by formulating the necessary constitutive relations. Chaboche’s model was chosen to describe the kinematic hardening law. Then, the numerical model necessary to solve the constitutive relations is developed, utilizing the Chaboche’s law with 3 terms and Euler’s implicit discretization. Then, the material parameters are identified for 304 and S460N steels and 6061-T6 aluminum alloy. The model is implemented in a FORTRAN routine, which is submitted to uniaxial and proportional and non-proportional multiaxial loading histories. The fatigue life data obtained from Lemaitre’s damage model is compared to experimental data. Then, a stress amplitude analysis is conducted and the numerical stresses are compared to experimental data. Damage evolution curves are also obtained for each material and loading. The results show that Lemaitre’s damage model describes adequately the behavior of the analyzed materials under low cycle fatigue, when low strain amplitudes are being applied to the specimen.

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2015. / Submitted by Albânia Cézar de Melo (albania@bce.unb.br) on 2015-12-04T13:07:44Z No. of bitstreams: 1 2015_RaphaelAraujoCardoso.pdf: 4524264 bytes, checksum: 5ea4d3c957b8492a91bd31fad78fdf80 (MD5) / Approved for entry into archive by Guimaraes Jacqueline(jacqueline.guimaraes@bce.unb.br) on 2016-03-28T11:33:00Z (GMT) No. of bitstreams: 1 2015_RaphaelAraujoCardoso.pdf: 4524264 bytes, checksum: 5ea4d3c957b8492a91bd31fad78fdf80 (MD5) / Made available in DSpace on 2016-03-28T11:33:00Z (GMT). No. of bitstreams: 1 2015_RaphaelAraujoCardoso.pdf: 4524264 bytes, checksum: 5ea4d3c957b8492a91bd31fad78fdf80 (MD5) / O objetivo desse trabalho é avaliar o fenômeno de propagação de trincas em condições de fretting. Uma metodologia mais genérica para estimar o fenômeno de parada de trincas curtas foi proposta e diferentes modelos para estimar a direção de iniciação e a posterior propagação de trincas também foram avaliados. Teorias clássicas como o método da distribuição das discordâncias e rotinas robustas em elementos finitos foram utilizadas para calcular os parâmetros mais importantes desse trabalho. Dados experimentais disponíveis na literatura foram utilizados para verificar a acurácia das metodologias em estudo. A metodologia proposta para avaliar o fenômeno de parada de trincas curtas foi capaz fornecer melhores resultados que outras presentes na literatura quando uma curva mais genérica para o fator de intensidade de tensão limiar (Δℎ), baseada no parâmetro material de Bazant, , foi utilizada. A respeito da estimativa da direção de iniciação de trincas, duas metodologias baseadas na Teoria das Distâncias Críticas foram avaliadas e um delas (o Método da Direção Crítica) foi capaz de fornecer satisfatoriamente a direção de iniciação das trincas, enquanto que a outra metodologia baseada em uma abordagem não-local de plano crítico levou a grandes erros nas estimativas. Duas outras diferentes metodologias também foram testadas para prever o caminho de propagação de trincas sendo que uma delas, baseada no cálculo do fator de intensidade de tensão de uma trinca infinitesimal emergindo de uma trinca preexistente, foi capaz de fornecer bons resultados, enquanto que a outra metodologia, baseada na faixa de tensão cisalhante nas proximidades da ponta da trinca, conduziu a resultados discrepantes em relação as observações experimentais. _____________________________________________________________________________________ ABSTRACT / The aim of this work is to evaluate the crack behaviour under fretting conditions. A more generic methodology was proposed to predict the short crack arrest phenomenon and different models to estimate the direction of crack initiation and further propagation were also assessed. Classical theories as the distribution dislocation technique and robust commercial FEM routines were used to calculate the most important mechanical parameters involved in these theories. Available experimental data were collected to verify the accuracy of the present methodologies. The methodology proposed here to evaluate short crack arrest was able to provide better estimates than other available in the literature when a more generic curve for the stress intensity factor threshold (Δℎ), based on the Bezant’s material parameter, , was used. Concerning the estimate of crack initiation direction, two methodologies based on the Theory of Critical Distances were assessed and one of them (the Critical Direction Method) could satisfactory provide the direction of crack initiation, whereas the other model, based on a non-local critical plane approach, led to high discrepancies. Two methodologies were also tested to predict crack propagation path and one of them, based on the calculation of the stress intensity factor of an infinitesimal kinked crack emerging from the original one, was able to provide good results, whereas the other methodology, based on the shear stress range near to the crack tip, led to inaccurate results.

No description available.