Ductile Fracture of Cabin Steel under Cold Metal Forming Conditions : 1st Report, Tension and Torsion Tests under Pressure

Tensile and torsional machines were developed fro testing under high hydrostatic pressures of up to 4 kbars; experiments were carried out using these machines to investigate the mechanics of ductile fracture of 0.25 % carbon steel. The strain at which fracture-nuclei (voids or cracks) begin to grow is determined by a method in which the hydrostatic pressure is changed during deformation, and it is shown that the strain at which growth of nuclei begins increases with pressure. The rate of nuclei-growth is suggested to depend on pressure and strain. Based on these results, a criterion for ductile-fracture strain in torsion tests is proposed taking the pressure history into account, and it is found to agree with the experimental results of various pressure histories.