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Prise en compte des contraintes résiduelles dans le dimensionnement en fatigue oligocyclique par des méthodes simplifiées

Abstract : Residual stresses are inherent to the manufacturing processes and can have a strong effect on the fatigue life of structures. Therefore, they shall be taken into account in fatigue design. In this PhD thesis, a fast design method is developed to take residual stresses into account in low cycle fatigue, either under tensile or compressive loadings. The main idea is to calculate analytically the stabilised stress-strain curve, at the critical point, by using a simplified method for confined plasticity. This method is based on a localisation law that extends energetic methods like Neuber to general multiaxial stress states. The localization law links the applied load to the local load at the critical point. It has to be identified on a finite element analysis of the structure under monotonic load. For this purpose, the elasto-plastic behaviour of the material is characterised from one single tensile test with loadings-unloadings. The behaviour law, identified sequentially, includes isotropic and kinematic hardenings with thresholds. This improves the stabilised mean stress prediction, which is used in the proposed fatigue criterion to represent the influence of the load ratio on the fatigue life. This criterion is identified on purely alternated tests (Rε=-1), and then validated under various tensile load ratios (Rε>-1) as well as compressive load ratios (Rε<-1). The methodology is validated on plate specimens with two semi-circular notches, which initially present different residual stresses states. The experimental evolution of local stresses during cyclic compressive (Rσ=-∞) and tensile (Rσ=0) repeated applied loads have been studied experimentally and compared to the numerical and analytical predictions. The same work has been achieved on the fatigue lives predictions. It shows that a slight conservatism, independent from the load ratio and the initial state, is obtained. Finally, an application of the method on T-Joints is realised to enlarge the scope of the method.
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Submitted on : Friday, January 13, 2017 - 9:56:11 AM
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  • HAL Id : tel-01433853, version 1

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Bruno Levieil. Prise en compte des contraintes résiduelles dans le dimensionnement en fatigue oligocyclique par des méthodes simplifiées. Mécanique des matériaux [physics.class-ph]. Université de Bretagne occidentale - Brest, 2016. Français. ⟨NNT : 2016BRES0070⟩. ⟨tel-01433853⟩

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