Local shear fracture properties in heat-affected zone of resistance spot-welded advanced high-strength steel

In the process of resistance spot welding of advanced high-strength steel (AHSS), the development of heat-affected zones (HAZs) considerably modifies the mechanical properties of the weld region. However, the limited reporting in the study of shear behavior in the HAZ hinders the accurate prediction of joint fracture and failure behavior. This study focused on the shear fracture behavior of resistance spot-welded AHSS. Given the limited extent of the HAZ, a miniature shear test was designed and shear fracture tests were conducted on JSC590, JSC980, and JSC1180. These tests facilitated the acquisition and compilation of data regarding the shear mechanical properties of diverse steel grades and their respective HAZs. A hardness-based empirical model for the strength coefficient and the strain-hardening exponent in Hollomon's law was introduced, and this model was subsequently integrated into finite element method calculations. The accuracy of the model was validated by shear strength reproductions, exhibiting errors within the range of 5.4%–13.5% and the averaged error was less than 10%. Further analyses confirmed that stress triaxiality at critical positions varied from 0 to 0.33, indicative of shear-dominant stress conditions. Moreover, the evolution of stress states revealed a notable association between the fracture surfaces across different stress states and steel grades. These findings fill the gap regarding the shear behavior of localized HAZs and expand the understanding of their mechanical behavior under various stress states. It will contribute to accurate fracture prediction by stress triaxiality based fracture criteria, such as Modified Mohr-Coulomb (MMC) model, applied to AHSS.