Calibration of Parameters for the Void Expansion Model of Q355D Steel and Its Welds

V-notched round bar specimens with five different notch angles were fabricated and tested for Q355D steel and its welds. Ductile fracture occurred in monotonic tensile tests on all these specimens. The fracture displacements of the specimens increased with the V-notch angle. The welded specimens exhibited slightly smaller fracture displacements than their corresponding base metal counterparts. Observations of the fracture surfaces showed that ductile fracture initiated at the notch tip for specimens V60， V75 and V90， while at the notch section center for specimens V105 and V120. Monotonic tensile tests on V-notched round bar specimens were simulated using the finite element method. The load-displacement curves obtained by numerical simulations agreed well with test results. The void expansion models were calibrated for the Q355D steel and its welds based on the tests and numerical simulations. The parameters in the void expansion model for the base metal and its welds were almost identical， indicating that the welds exhibited comparable superior ductility to the base metal. The fracture locations predicted by the void expansion model were consistent with the test observations for all V-notched round bar specimens. The predicted fracture displacements for all V-notched specimens differed from test results by less than 15%， validating the rationality of the calibrated void expansion model. This also confirmed the applicability of the void expansion model for the analysis of ductile fracture of V-notched round bar specimens initiating at different locations.