Predicting mechanical behavior of half-blanked components
Résumé
Half-blanking of thick steel sheets is a metal forming process used to manufacture automotive seat recliner parts. During the forming process and in-use conditions (in case of crash) the material can be submitted to a high level of plastic strain and, in some cases, ductile damage. Recliners play an important role in the safety of passengers. Accurate computation results are thus needed. Forming stages have to be taken in account and damage and failure have to be modelled accurately. Two laboratory tests are developed to study the mechanical behaviour of half-blanked components. First, a cylindrical relief is half-blanked in a steel sheet sample. Then the cylindrical relief is wrenched using a shearing tool. During the tests, load and displacement are recorded. These tests enable the observation of failure mechanisms (SEM fracture observations) and give experimental data to validate numerical computations (geometries and load-displacement curves). During the wrenching test, a competition between ductile and shear failure is observed. Damage is modeled with a continuum mechanics based model (Lemaitre) and a phenomenological model (Xue-Wierzbicki). In the second one, the third invariant of the stress tensor is used to make difference between ductile and shear failure. Mechanical tests are performed to identify parameters model by inverse analysis. Tests are performed on different samples in order to have different stress states (stress triaxiality and Lode angle). In order to take into account material history, wrenching is performed with or without accounting for the half-blanking process. During both stages, large deformations are encountered. Automatic remeshing is needed and the finite element software Forge® is used. References : [1] W.F. Fan, J.H. Li, An investigation on the damage of AISI-1045 and AISI-1025 steels in fineblanking with negative clearance, Material Science and Engineering A 499, Elsevier, 48-251, (2009) [2] S. Fayolle, Etude de la modélisation de la pose et de la tenue mécanique des assemblages par déformation plastique, Thèse doctorale, École Nationale Supérieure des Mines de Paris, (2008) [3] J. Lemaitre and J.L. Chaboche, Mécanique des matériaux solides, Dunod, Paris, (2001) [4] L. Xue, T. Wierzbicki, Ductile fracture initiation and propagation modeling using damage plasticity theory, Engineering Fracture Mechanics 75, Elsevier, 3276-3293, (2008) [5] P.F. Zheng, L.C. Chan, T.C. Lee, Finite-element analysis of a combined fine-blanking and extrusion process, International Journal for Numerical Methods in Engineering 66, Wiley, 404- 430, (2006)