The Impact Opening of Spot Welds by Plane Tensile Pulses

We investigate the strength of resistance spot welds (RSW) of QP 980CR steel under shock loading conditions by using a projectile plate of DC53DZ steel driven by a one-stage gas gun which impacts the welded plate at a velocity V0. The velocity histories of the free surfaces of the spot weld and the free part of the welded plate are measured with the Laser Velocity Interferometer System for Any Reflector (VISAR). We evaluate the tensile stresses in the spot weld and the free part of the welded plate from the measured velocity histories by using the characteristic theory. The welded plates opened purely under certain plane tensile pulses induced by the interactions of the release waves. We find that the RSW does not fail until the impact velocity V0 is greater than 0.2 mm/μs. Depending on the impact velocity a partial interfacial failure (PIF) mode or an interfacial failure (IF) mode of the spot welds may initiate under the combined tensile stresses in the free parts and the spot weld of the welded plate. The results of the scanning electron microscope (SEM) investigation of the evolution of microdamage in the recovered specimens of PIF mode show microvoid coalescence mechanisms, while that in the recovered specimen of the IF mode show the evolution of the microcracks.