Methodology to assess fracture during crash simulation: fracture strain criteria and their calibration

Abstract

The use of Advanced High Strength Steels (AHSS) has greatly increased this last decade in the automotive industry. Because of their crash performance and their weight saving potential, these grades constitute a possible solution to achieve the safety and environmental regulations objectives. Nevertheless, the increase of tensile strength of these materials is generally associated with a loss of ductility compared to conventional steels. Thus, the prediction of their failure in crash loading conditions become of great importance for the design of vehicles. This paper proposes to calibrate for any AHSS, as Dual-Phase or Press Hardened Steels, different failure criteria, available in finite element software. First, specific tests and methodologies for strain measurement needed for models calibration are exposed. Second, an overview of these tested models and the procedure applied to take into account mesh dependency are provided. Finally, simulations results are compared with experiment on a real automotive component.

Crashworthiness evaluation of press hardened steels with different lath-like microstructures.

“…For this purpose, it is tested in a universal tensile machine until rupture. It is calculated by the equation 1 [12], where t0 corresponds to the initial thickness and t to the minimum thickness after the test. This thickness was measured by optical microscopy.…”

Force Prediction in Robotized Ultrasonic Sheet Metal Forming Based on Finite Element Analysis and Artificial Neural Networks

“…7, where the solid line represents the calibrated Power-Law material curve. The Power-Law equation is provided below: Although the fracture strain is stress state dependent [22,23], the value obtained in the uniaxial test may differ from the failure strain obtained in the cupping test where the biaxial tension is dominant. In case of the cupping test the failure strain is larger than in the uniaxial tensile test.…”

“…In case of the cupping test the failure strain is larger than in the uniaxial tensile test. During the incremental forming process the strain path is nonlinear [23], therefore not only the uniaxial failure strain but also the conventional forming limit diagram criterion can cause inaccurate failure prediction.…”