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Influence de l'historique du chargement sur la fermeture induite par la plasticité et la forme d'une fissure de fatigue

Abstract : The objective of this study is to provide a three-dimensional predictive numerical tool of the evolution of the curvature the crack front during the propagation of a fatigue crack, taking into account the plasticity induced crack closure. Targeted testing performed on a CT-50 austenitic 304L stainless steel specimen monitored the stabilized crack front shape for a long crack for different load ratios R and different amplitudes ΔK of the stress intensity factor (FIC). In order to avoid any influence of the loading history, a constant value of ΔK has been applied. A 3D model, using ABAQUS® and PYTHON programming language has been developed. A contact without friction is placed on the plane of the crack to take into account the phenomenon of closure.Several driving forces of crack were studied, according to assumptions of linear elastic or elastoplastic fracture mechanics. Initially, two parallel simulations are carried out (elastic and plastic), in order to measure, on each node of the current crack front, the value of the local effective range of the stress intensity factor considered as the driving force in this first case. In this context, several methods of calculating the local stress intensity factor along the crack front were implemented because a previous study [1] had clearly shown that the Shih and Asaro method used by ABAQUS® does not allow to correctly account for free surface effects. It appears that the calculation of the stress intensity factor, based on the stress field in the vicinity of the crack leads to more precise results along the crack front and above all, has the considerable advantage of not making any assumption d evolution of the stress state over the entire thickness of the test specimen. In addition, other elastoplastic driving forces are also studied: the plastic opening displacement at the crack tip, and the strain intensity factor.The propagation of the crack front is obtained numerically by successive advances on each node of the front, along the thickness, using propagation laws associated with these different driving forces. A remeshing procedure is then implemented, and many steps are performed, with reconstruction at each step of the plastic wake. Different stabilization conditions are introduced, allowing a comparison of experimental and predicted stabilized crack front shapes for the different driving forces. The ensuing discussion highlights the improvements made, but also the limitations, which naturally leads the author to propose further perspectives.
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Submitted on : Friday, May 21, 2021 - 2:10:09 PM
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Wissam Taleb. Influence de l'historique du chargement sur la fermeture induite par la plasticité et la forme d'une fissure de fatigue. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2021. Français. ⟨NNT : 2021ESMA0003⟩. ⟨tel-03232243⟩

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