Dynamic energy absorption of ultrafine-grained TWIP steel under axial impact loading

Abstract

This research focuses on studying the dynamic energy absorption property of a micro-alloyed TWIP steel, which was proposed to act as a connection part between car front bumper and chassis in middle-class cars for vehicle safety. The studied TWIP steel was designed based on stacking fault energy of 25mJ/m2. The as-cast steel was deformed in hot and cold rolling to 2 mm thick sheets. Subsequently, recrystallization annealing was applied to the heavily cold-worked steel at different temperatures to obtain different ultrafine grain structures. The mechanical properties were determined using tensile tests. It was observed that at 900°C, the optimal temperature for strengthening by vanadium carbide precipitation, it was too low to complete recrystallization. However, at 1000°C, an ultrafine-grained structure was formed with high yield, tensile strengths and elongation of about 700MPa, 1100MPa and 30% respectively. Accordingly, TWIP steel was used for crash analysis simulation using ANSYS Workbench R14.5. Thin-walled square columns of that steel were employed for energy absorbance during a collision regarding progressive plastic deformation. The crashworthiness criteria were studied under different impact conditions with thicknesses of 0.25, 0.5, 0.75 and 1 mm. Simulation results showed high initial peak force during the impact. Hence, a trigger mechanism of an external tapered plunger was proposed to reduce it. This combination of new material and innovative design promises enhancement car safety.