SIZE EFFECT ON THE LOAD-DISPLACEMENT CURVES OF COMPACT SPECIMENS OF SUS 316 STEEL.

The size effect on the crack growth in SUS 316 steel was studied by observations of load-displacement curves of many proportional compact specimens with various nominal widths. When the thickness was less than 0. 2 times the width, the critical crack-tip opening-displacement (CTOD) for the start of steady crack growth was proportional to the thickness. The proportional constant was expressed by the experimental constants (yield stress, work-hardening parameters and fracture true stress) obtained by the unidirectional tensile tests. It was concluded that a ductile crack grows when the normal stress ahead of the crack-tip exceeds the fracture true stress of the materials.