Simulation de la fatigue par chocs, par la fatigue conventionnelle

Abstract : The aim of this thesis is to study the simulation of impact fatigue with the help of conventionnal fatigue, on the following materials : 30 NCD 16 steel, Marval 18 h steel, Al/SiC composite. In a first step, we have examined the evolution of crack growth rate with respect to the maximum peak value of each loading. This study has shown that the influence of the strain rate of both kinds of fatigue loadings, is no significant. All the loading peaks for impact fatigue has been considered in a second step. It has been necessary to make use of counting methods in order to transform this loading in a constant amplitude loading cycles. The computation of the crack growth rate from these results, has been made using cumulative growth length and equivalent loading methods. The application of both concepts, reveals that small oscillations in the amplitude of the impact fatigue signal has no effect on the crack growth rate. On another hand, initiation tests has shown that the numbers of cycles to initiation corresponding respectively to the equivalent loading and the programmed loading, are quite similar. Last, the results of initiation tests has been analysed using a new criterion based on the notch stress intensity factor. A quite reasonnable scattering of results with respect to that observed with an analysis using the crack stress intensity factor, has been noticed. From this point of view, the validity of this criterion has been emphasised
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Mamadou Ndiaye. Simulation de la fatigue par chocs, par la fatigue conventionnelle. Autre. Université Paul Verlaine - Metz, 1994. Français. ⟨NNT : 1994METZ023S⟩. ⟨tel-01776076⟩

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