Prediction of Perpendicular-to-weldline Crack in Hemispherical Punch Stretching of High-strength Steel Tailor-welded Blanks

Cracks perpendicular to the weld line in a tailor-welded blank fabricated from high-strength steel plates were predicted using the integral-type ductile fracture model proposed by Cockcroft and Latham. The test material consisted of laser-welded steel sheets with tensile strengths of 1470 and 440 MPa. These perpendicular cracks were induced by a hemispherical punch stretching test using a punch with a diameter of 20 mm. Finite element models replicating the experimental setup were developed, incorporating a polyline flow stress (PLFS) model. In the PLFS model, the flow stress before local necking was based on experimental tensile test data, whereas the flow stress in the post necking region was extrapolated by autonomously driven finite element analysis using an automatic optimization system. In addition, to determine the optimal modeling approach, finite element analyses were conducted both with and without the consideration of the heat-affected zone (HAZ). As a result, the model that included the HAZ in the 1470 MPa steel, located adjacent to the weld line, successfully reproduced the experimentally observed cracks perpendicular to the weld line.