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 spli t 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 revea led that the most favourable position of crack initiation is grain boundari es. On the other hand grain boundaries are an effective obstruction for cra ck propagation. It is easy for cracks to initiate and grow in grains with s traight slip bands, but difficult in grains with cross slip bands. The dama ge caused by micro-pits growing and linking up are quite shallow. (C) 1999 Elsevier Science S.A. All rights reserved.