In order to examine effects of the grain boundary on initiation of fatigue cracks, aluminum bicrystals were produced with Bridgman method. They were tested by a bending fatigue testing machine under the constant strain amplitude of 0.18%.
It has been found that conditions necessary for the initiation of fatigue cracks along primary slip bands in the grain boundary affected-regions are as follows:
(1) Dislocations parallel to the grain boundary planes are of nearly the screw type.
(2) Cross slip on the primary slip systems can be promoted due to incompatibility of elastic and plastic strains at grain boudaries.
