Micromechanisms of fatigue crack nucleation and short crack growth in a low carbon steel under low cycle impact fatigue loading

Abstract

An experimental investigation has been conducted to study micromechanisms of short crack initiation and propagation in a low carbon steel under low cycle impact fatigue loading. The results indicated that the most favorable site for crack nucleation was grain boundaries. On the other hand grain boundaries were the effective obstruction for short crack growth. The progressive process of crack growing across a grain boundary involved crack tip blunting, plastic flow zone forming, crack branching and only one of the branches growing continuously. Crack nucleation and propagation along slip bands were difficult in the grains with wavy or cross slip bands, and they were easy in the grains with straight slip bands. The short crack growth rate fluctuated periodically until the crack length reached a critical value and then crack growth accelerated.