Specimen geometry design for plasticity and fracture characterization of sheet metal under high testing speed and various stress states

To model a vehicle crash event using the finite element (FE) method, accurate material properties of automotive sheet metals at high strain rates and various stress states need to be known. In this paper, a series of specimen geometries were designed for dynamic tensile tests in a servo-hydraulic tensile machine to get rid of the system ringing effect. These specimen geometries, which consist of different Stress triaxialities and Lode angle parameters, were optimized according to a similar physical principle as that used for the Gen. III specimen of Fang and Grams using FE simulations. Oscillation-free forces were obtained during the high-speed tests in the strain rate range of up to 103 s−1 using specimens that have a novel design. The deformation and local strain fields of the specimens were measured using digital image correlation (DIC) techniques. Furthermore, the deformation and fracture behavior of a micro-alloyed steel (H340) were characterized and analyzed. The determination of the model parameters for plasticity, damage/fracture modeling, and the material’s strain-rate dependency could be conducted more accurately based on the improved oscillation-free force measurements, which resulted in an improved prediction of the plasticity and fracture behavior of the investigated steel.