Investigation of dynamic tensile mechanical responses and deformation mechanism at high strain rates in a TWIP steel

Abstract

In view of the potential demand for the materials with excellent dynamic mechanical behavior in protective construction, the dynamic tensile mechanical properities and deformation mechanism of twinning-induced plasticity (TWIP) steel at various high strain rates were investigated in this paper by combining test research and numerical simulation. In order to explore the impact of strain rates on mechanical behaviors within the tested range, a split Hopkinson tensile bar (SHTB) was utilized to measure the mechanical responses of TWIP steel ranging from 1000 s−1 to 6500 s−1. The Johnson–Cook (J-C) dynamic constitutive model was established based on the mechanical test results, and the mechanical properties were studied by using ANSYS/LS-DYNA. EBSD and TEM were employed to investigate the microstructure evolution of TWIP steel under dynamic loading. The results demonstrate that both strength and plasticity increase with increasing strain rate, demonstrating positive strain rate sensitivity (PSRS) which is primarily due to the activation of multiple twin systems at higher strain rates. As the strain rate increases, the mean free path of dislocation slip reduces, causing a higher strain hardening rate. The critical shear stress required for twinning is almost unchanged with an increase in strain rate, while the shear stress required for dislocation increases consistently. As the strain rate exceeds 3000 s−1, the critical shear stress required for dislocation becomes greater than that for twinning. With increasing strain rate, the proportion of secondary twins in TWIP steel rises and the deformation twins are bent when the strain rate is 6500 s−1 owing to the effect of dislocations and stacking faults. The production of nanoscale twins at higher strain rates is a beneficial phenomenon, as it enhances both strength and plasticity. The deformation twins become thinner with an increase in strain rate, leading to a rise in the stress needed for the motion of dislocations to pass the twins, which contributes to the improvement of strength in TWIP steel. The slip systems that deforms at a disadvange have new orientations because of defromation twins. The established J-C model is appropriate well for analyzing the mechanical properties of TWIP steel in the tested range of strain rates accoring to the fingdings of test and numerical simulation. Establishing the connection of microstructure and macroscopic behavior of TWIP steel could provide a guidance for the its further study and the application in the fields of impact resistance and anti-explosion.