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Etude du comportement en fatigue des fissures semi-elliptiques : application aux plaques en flexion et aux tubes sous pression interne

Abstract : The propagation of a fatigue crack emanating from an initial surface defect in a three dimensionnal mechanically loaded structure is characterized by the fact that the defect takes an elliptical shape which evolutes with the time. The safety of constructions and, particulary of pressure vessels, implies to know the the evolution of this defect with the cyclic loading. The safety concepts, such as "leak before break", use the depth and shape of the elliptical defect and need the knowledge of the propagation law. This evolution is often complex and is considered as governed by various approaches all based on the assumption that the propagation of a crack is sensitive to stress gradient and, then, governed by the stress intensity factor. Three approaches will be considered, local, global and semi-local. Results from crack propagation experiments and finite elements calculations have been analysed in terms of stress intensity factor evolution along the semi-elliptical crack front. These analysis were made on plates and tubes, for various a/c and a/B ratios. Our results have been used to determine the crack propagatio parameters mi and Ci of the Paris' law. These coefficients are related to the solution for a semi-elliptical crack at the deepest point and on surface and for two loading ratios (R=0.1 and R=0.3 for a plate, R=0.3 for a tube). These results have shown that is some discrepancy for both the value and the evolution of the stress intensity factor, with respect to those obtained with the method given by Newmann and Raju or Cruse and Besuner. This discrepancy is due to the density and the kind of meshing used. Our results are a contribution to the no-solved problem of the propagation of semi-elliptical fatigue crack
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Taoufik Boukharouba. Etude du comportement en fatigue des fissures semi-elliptiques : application aux plaques en flexion et aux tubes sous pression interne. Sciences de l'ingénieur [physics]. Université Paul Verlaine - Metz, 1995. Français. ⟨NNT : 1995METZ016S⟩. ⟨tel-01776911⟩



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