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 welded
DP1000-GI dual-phase high-strength steel in order to derive the mechanical
response of the welds. Notched micro-cantilevers were milled using focused ion
beam milling at the base metal, inter-critical, fine-grained and coarse-grained
heat affected zones, and fusion zone. It was shown that due to large plastic
yielding, linear-elastic fracture mechanics are inapplicable. To evaluate the
fracture toughness of different weld zones, cyclic loading was applied to track
the crack size and the conditional fracture toughness of weld zones was measured using crack tip opening displacement and J-integral methods. It was
found that micro-cantilever bending method provides insight to the fracture
toughness and local mechanical response of different weld zones. The results
obtained can be used to make an accurate correlation between resistance spot
welding process, microstructure and mechanical response of DP1000-GI dualphase high-strength steel welds.