Micromechanical evaluation of DP1000-GI dual-phase high-strength steel resistance spot weld

In situ micro-cantilever bending tests were carried out on resistance spot weldedDP1000-GI dual-phase high-strength steel in order to derive the mechanicalresponse of the welds. Notched micro-cantilevers were milled using focused ionbeam milling at the base metal, inter-critical, fine-grained and coarse-grainedheat affected zones, and fusion zone. It was shown that due to large plasticyielding, linear-elastic fracture mechanics are inapplicable. To evaluate thefracture toughness of different weld zones, cyclic loading was applied to trackthe crack size and the conditional fracture toughness of weld zones was measured using crack tip opening displacement and J-integral methods. It wasfound that micro-cantilever bending method provides insight to the fracturetoughness and local mechanical response of different weld zones. The resultsobtained can be used to make an accurate correlation between resistance spotwelding process, microstructure and mechanical response of DP1000-GI dualphase high-strength steel welds.