Relation Between Notch Tensile Strength and Stress Triaxiality. A Method of Increasing Notch Tensile Strength.

Abstract

Notch tensile strength of circumferentially notched cylindrical bars with ring protuberances on both notch shoulders is investigated. The protuberances are employed to increase stress triaxiality near the net section. The notch tensile strength increases with increasing diameter and length of the protuberances. The protuberances quenched only in the thin layer from those surfaces produce higher notch tensile strength than the unquenched protuberances. The stress triaxiality factor obtained from FEM calculation is proportional to NSR or the ratio of notch tensile strength to unnotch tensile strength. FEM simulation shows that when both notch shoulders are quenched ideally to higher yield stress, NSR of a shallow notch is nearly equal to NSR of a deep notch ; NSR of a deep notch is much higher than NSR of a shallow notch unless the quench is performed. This indicates that notch shoulders are one of the most important factors determining notch tensile strength.