An observation of crack initiation and early crack growth under impact fatigue loading

The micro-characteristics of crack initiation and early crack growth of low carbon steels under low cyclic impact fatigue loading were studied. A split Hopkinson’s bar was used in the impact fatigue test, and SEM was used to examine the evolution of the surface on the post-test specimen. It is revealed that the most favourable position of crack initiation is grain boundaries. On the other hand grain boundaries are an effective obstruction for crack propagation. It is easy for cracks to initiate and grow in grains with straight slip bands, but difficult in grains with cross slip bands. The damage caused by micro-pits growing and linking up are quite shallow.