Role of deformation bands in fatigue crack nucleation and propagation in copper crystals

Abstract

The deformation behaviour of copper crystals of [ 1 22] orientation under low strain amplitude cyclic loading is reported. Specimens with square cross section have been cycled to failure and changes in surface topography have been studied using scanning electron microscopy and X-ray Laue techniques. Two sets of deformation bands are shown to form on all four sides of the specimens prior to crack propagation and to lead to the development of surface waviness. The bands form on 45° planes of maximum shear and their structure is discussed. The exact location of the crack nucleation site within a deformation band is shown to be influenced by the slip system with the greatest Schmid factor. The selection of the [ 1 22] crystal orientation, which provides two equally stressed slip systems on the primary plane, is believed to be one of the major factors influencing the deformation characteristics observed, the other being the macroscopic state of stress.