Mechanism of intergranular fatigue crack growth in copper polycrystal

Abstract

Polycrystalline copper specimens (notched and smooth) were subjected to constant strain amplitude loading and the fatigue fracture surface was inspected and analyzed. The majority of facets on the fracture surfaces indicated intercrystalline fracture. Facets with well-developed relief were inspected. The relief was formed by persistent slip markings consisting of extrusions and intrusions similar to that on the specimen surface in the cyclic plastic zone of the growing crack. The mechanism of grain boundary cracking in the cyclic plastic zone of the growing crack similar to that recently suggested for intergranular crack initiation was drawn up. The crack growth mechanism based on the interconnection of cracked grain boundaries and the tear of the islands between them was proposed. The effect of grain size, orientation, and crack growth rate on the grain boundary cracking was discussed. Preliminary results on other FCC materials indicate a more general validity of the proposed intergranular fatigue crack growth mechanism.