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Effet du formage à froid sur la tenue en fatigue à la propagation d'une structure d'alliage Al2024T351

Abstract : The Dassault Aviation Group designs and builds a wide range of aircraft models each year, for both private and military use. Some structural parts of the aircraft, in the form of reinforced stiffener panels machined directly into the bulk of Al2024T351 thick plates are studied. As part of the shaping process, these elements must be cold formed to give their final curvature. This process severely plastified some regions of the structure. In addition, these zones are likely to constitute sites of initiation and propagation of fatigue cracks.This study aims to analyze the interactions between the plastic phenomena induced by cold forming and the propagation of a fatigue crack during fatigue service loading. This thesis is conducted according to the following approach:An instrumented cold forming test has been performed on two self-stiffening technological specimens. From an experimental base of tensile tests, a model of anisotropic plastic behavior of the plate was proposed allowing the development of a cold forming structure simulation and an analysis of the residual state of the material following the process. Using all the results about residual plastic state, a compression and traction test on large test pieces has been performed (54 mm diameter slugs and flat tensile test pieces of 75x55 mm section) whose purpose is to produce a homogeneous volume of pre-deformed material in compression and traction (+/-10 % of plasticity) .A large campaign of fatigue tests has been realized on oligocyclic specimens and specimens of propagation (Compact Tension) extracted from the volumes of original and pre-deformed material allowing the characterization of the effects of the pre-deformation on the fatigue properties. A modified Forman propagation model has been identified from the velocity curves.Finally, self-stiffened structures formed have been subjected to a cyclic loading and the fatigue initiation and propagation behavior has been observed experimentally. A simulation of the fatigue loading of the structure after forming has been proposed. The Z-crack module of the Z-set finite element code associated with the propagation model allowed to simulate the propagation of a fatigue crack within the structure.
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Submitted on : Tuesday, January 14, 2020 - 3:08:46 PM
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  • HAL Id : tel-02439234, version 1

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Raphael Cusset. Effet du formage à froid sur la tenue en fatigue à la propagation d'une structure d'alliage Al2024T351. Mécanique des matériaux [physics.class-ph]. PSL Research University, 2019. Français. ⟨NNT : 2019PSLEM036⟩. ⟨tel-02439234v1⟩

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