Fatigue crack propagation and grain boundary

Compact tension (CT) shaped copper bicrystals containing the Sigma 3(111), Sigma 9(221) or Random [110] tilt boundaries either perpendicular or parallel to the tensile axis (TA) were tested to examine the effect of grain boundary (GB) structure on fatigue crack initiation and propagation. The different crack behavior was noted with respect to the GB type, Pure intragranular fracture was observed in the specimen with Sigma 3 boundary in contrast to the bicrystal having a random boundary where an intergranular crack was initiated and propagated. Unstable crack behavior showing preferentially mixed fracture is a feature of the bicrystal with Sigma 9 boundary.