Shear fatigue cracking of twin boundary and grain boundary without dislocation impingement

Cu bicrystals with a twin boundary (TB) and a {1 1 1} grain boundary (GB) were cyclically deformed. It is shown that the slip bands in the two component grains of both bicrystals are parallel to the TB and GB, respectively. Despite no piling up of dislocations, fatigue cracks still nucleate preferentially along the TB and GB in a shearing mode. The experimental results demonstrate that the inclined interfaces of {1 1 1} plane usually show low resistance to the shear fatigue cracking.