Search

Shear localization is a fundamental and widely observed non-equilibrium phenomenon in metallic materials subjected to impulsive loadings. Despite extensive research over several decades, the evolution of shear bands still remains poorly understood. In this study, we propose a two-stage model to describe the evolution of thermoplastic shear band, where the effects of strain hardening, strain-rate hardening, and thermal softening are involved. Our analysis reveals that the growth of thermoplastic shear band is derived by the competition between momentum diffusion and thermal diffusion processes, which is controlled by the solid-state equivalent of the Prandtl number. By incorporating these factors into our model, we find that the presence of hardening effect retards the evolution of shear bands, resulting in a wider shear band and increased dissipation of energy. Theoretical calculation results of shear bandwidth, shear band strain, propagation velocity, process zone geometry and dimensions, critical dissipation energy, shear band toughness, and shear band spacing are well consistent with available experimental data. Additionally, we explore the potential transition to turbulence controlled by Reynolds number within shear bands and investigate the influence of the Taylor-Quinney coefficient on the evolution of shear bands. These findings are expected to offer valuable insights into the mechanism of shear band evolution.

Ballistic impact response of resistance-spot-welded (RSW) double-layered (2 × 1.6 mm) plates (190 mm × 150 mm) for Q&P980 steel impacted by a round-nosed steel bullet (12 mm diameter and 30 mm length) was investigated by using gas gun and high-speed camera system. The RSW specimens were spot welded using a 6 mm diameter electrode face producing a 7.2 mm diameter fusion zone of the spot weld. The ballistic curve and energy balance for the tests of the spot weld of the RSW specimens at different velocity were analyzed to characterize the ballistic behavior of the RSW specimens under bullet impact. The fracture mechanisms of the RSW specimens under bullet impact were presented. For the tests below the ballistic limit, the cracks initiated from the notch-tip and propagated along the faying surface or obliquely through the thickness depending on the impact velocity. For the tests above the ballistic limit, the plug fracture in the front plate of the RSW specimen could be caused by the thinning-induced necking in the BM near the HAZ, while the plug fracture in the rear plate of the RSW specimens may be consist of the circumferential cracking from the rear surface and the bending fracture of the hinged part of material. The effects of the electrode indentation and the weld interfaces on deformation and fracture of the RSW specimens under bullet impact were revealed. For the tests above the ballistic limit, the circumferential fracture from the rear surface of the RSW specimens was always initiated along the interior periphery of the electrode indentation and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface. When the circumferential crack also formed outside the electrode indentation, the fracture on the BM/HAZ interface could be found. On the front plate of the RSW specimens, the shear/bending induced cracking from the notch-tip were observed and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.