Ductile Crack Initiation Behavior of Prestrained Steels

Abstract

Ductile crack initiation behaviors were experimentally and analytically investigated using compressively prestrained notched round bar specimen (lower stress triaxiality condition) and four point bend specimen (higher stress triaxiality condition). The materials used were SM400B and HT780. It was observed that ductile crack initiation of notched round bar specimen occurred at the center of specimen and was caused by coalescence of micro voids. Ductile limit curves, which are the relationships between equivalent plastic strain and stress triaxiality factor at ductile crack initiation, were obtained using FE-analyses and experimental results. Ductile crack initiation of four point bend specimens as cracked specimens could be evaluated using ductile crack initiation limit curves obtained from notched round bar specimens if the positions of void nucleation at crack tip are properly considered. It has been found that ductile crack initiation limits can be evaluated using ductile limit curves under both low and high constraint conditions (stress triaxiality conditions.