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

An experimental investigation has been conducted to study micromechanisms o f short crack initiation and propagation in a low carbon steel under low cy cle impact fatigue loading. The results indicated that the most favorable s ite for crack nucleation was grain boundaries. On the other hand grain boun daries were the effective obstruction for short crack growth. The progressi ve process of crack growing across a grain boundary involved crack tip blun ting, plastic flow zone forming, crack branching and only one of the branch es growing continuously. Crack nucleation and propagation along slip bands were difficult in the grains with wavy or cross slip bands, and they were e asy in the grains with straight slip bands. The short crack growth rate flu ctuated periodically until the crack length reached a critical value and th en crack growth accelerated. (C) 1999 Elsevier Science Ltd. All rights rese rved.