Abstract

The main objective of this work is to gain a fundamental understanding of the behavior characteristics of a quenched and partitioned (Q&P) steel at high strain rates by employing Split Hopkinson bar testing, drop weight impact testing, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques. The deformation process is investigated at macro- and micro-scales in two deformation modes: uniaxial and biaxial. The speeds are 8 – 14 m/s (corresponding to strain rates of 500 – 1000 s-1) in Split Hopkinson bar testing and 3 – 7 m/s in drop weight impact testing, respectively. The main outcomes of the first year activities can be roughly generalized as follows. The yield strength (YS) and ultimate tensile strength (UTS) during high strain rate uniaxial tensile test are well above compared to those during testing with conventional strain rates. The 1 mm sheet of the studied Q&P steel is able to withstand up to 110 J impact energy without any cracking, which is much higher than the energy absorption capability of the AISI 304 and TRIP 1000 steels, where the limits are below 60 J. Additionally, 53.40% of true strain was achieved in drop weight impact test of 110 J with no cracking, indicating superior crashworthiness of the material. Fracture surface analysis indicates a ductile fracture during testing in both modes (uniaxial and biaxial with impact energy of 120 J). Chisel point dimples and microcracks are main features of the samples after drop weight testing, while the specimens after uniaxial tensile testing show a homogeneous ductile fracture surface consisting of deeper dimples.