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Numerical modelling of crack initiation and propagation in ductile metallic sheets for crash simulations

Abstract : In the event of a car crash, parts made of metal sheets are subjected to failure. Failure of ductile materials is currentlynot reliably predicted in an industrial context, involving additional costs and delays in the design process. This issue isthen addressed in this Ph.D thesis work of the PSA Group carried out in collaboration with Onera and the Centre des Matériaux. The aim of this work is to develop and implement a reliable numerical strategy for crack prediction using the Finite Element Method (FE) in automotive crash simulations. A first part of this work consists in characterizing and then modelling the plastic and fracture behavior of a representative ductile material: the DP450 steel sheets. To do so, tests are performed over a wide range of loading rates, stress triaxialities, and at different temperatures. From the obtained results,a numerical constitutive model is built by taking into account the different observed phenomena influencing crack initiationand propagation: plasticity, strain-rate effects and damage. The constitutive model thus enables to take into account mostof the observed phenomena. However, the use of softening models for modelling damage and thermal effects at highloading rate leads to a pathological dependence of the results on the mesh size and the mesh orientation. This problem issolved by the implementation of a non-local regularization method adapted to dynamic explicit computations. A non-localvariable is then computed through the enrichment of finite elements (continuum and shell). It is therefore treated as a new degree of freedom, which facilitates the exchange of data between the elements while preserving the parallelizationof the code. This variable is then introduced into the constitutive equations, allowing to obtain mesh independent results.The validation of the proposed approach is finally realized through the simulation of experimental results.
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  • HAL Id : tel-02518318, version 1

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Valentin Davaze. Numerical modelling of crack initiation and propagation in ductile metallic sheets for crash simulations. Mechanics of materials [physics.class-ph]. PSL Research University, 2019. English. ⟨NNT : 2019PSLEM060⟩. ⟨tel-02518318⟩

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