MODELISATION ET SIMULATION DE STRICTION ET DE PLISSEMENT EN EMBOUTISSAGE DE TOLES MINCES ET HYDROFORMAGE DE TUBES MINCES

摘要

The work carried out the development of new criteria for the detection of necking/bursting and wrinkling/buckling defects during hydroforming and stamping of thin components. Localised necking is looked as an instability of material flow. To predict such instability, a Linear Stability Analysis (LSA) by perturbation method is chosen. The initial 2D approach has been extended to a more realistic 3D modelling. This analysis allows considering new instability modes. Moreover, the developed criterion has been improved by the determination of the instability threshold that differentiates absolute instability and effective instability. Forming Limit Curves are built to look at the influence of some material parameters on tensile defects. The LSA applied to a pure bending test shows that necking can not occur on such a test. About wrinkling, this defect does not seem to be an instability phenomenon but a bifurcation one. In this work, a new analysis based on plate equilibrium is developed. Moreover, the Nordlund & Häggblad qualitative analysis is considered. A third criterion has been developed in annex. The necking/bursting and wrinkling/buckling analyses have been integrated in the simulation code POLYFOFORM?. The influence of stamping and hydroforming processes and material parameters on the defects prediction during simulation is shown. Experimental validation of the prediction has been realised on a tube hammering hydroforming process. The influence of the new process parameters on defects occurrence is looked at.