A shear band decohesion model for small fatigue carck growth in an ultra-fine grain aluminium alloy

Abstract A study of small fatigue crack growth behaviour of an ultra-fine grain size aluminum alloy IN 9052 has been carried out. Specimens were tested in tension–tension at R∼0.1 in laboratory air and in the vacuum chamber of a field emission gun scanning electron microscope. Loading and unloading experiments were carried out within the SEM to study the displacements of the crack faces, the shape change at the crack tip, the shear bands around the crack tip and the fatigue crack growth mechanism. The in-situ SEM observations revealed that shear bands formed in the crack tip region were directly associated with the growth mechanism of the crack. The shear bands localized the decohesion in the crack tip region and the cracking along the shear bands was observed to occur during the loading part of the load cycle. The overall behaviour of the crack tip region subjected to cyclic loading is summarized by a qualitative model for small crack growth in an ultra-fine grained material.