On the formation of fatigue cracks at twin boundaries

Fatigue crack formation at twin boundaries in OFHC copper has been studied as a function of twin boundary orientation with respect to applied stress. The operation of slip planes immediately adjacent to and parallel to the twin boundaries was found to be essential for crack formation at the boundaries. The role of twin boundary steps as dislocation sources is discussed with respect to increased plastic deformation at twin boundaries. Finally the cracking of alternate twin boundaries was observed and correlated with the operation of secondary slip planes.