Crack initiation and growth under far-field cyclic compression: theory, experiments and applications

Abstract

The application of cyclic compressive loads can result in the propagation of fatigue cracks from stress concentrations (i.e., notch, void, etc.). Such cracks, initiated under the influence of residual tensile stresses in the vicinity of the stress concentration, generally grow at a progressively decreasing rate before arresting completely. Although the occurrence of this phenomenon had long been recognized, very little is known about the mechanics and mechanisms of crack advance under imposed cyclic compressive loads. In this paper, we examine the influence of stress state, crack-tip plasticity, load range and microstructure on the characteristics of crack initiation and (short crack) growth under fully compressive far-field cyclic loads. Some important applications of the phenomenon of crack initiation under far-field cyclic compression to the study of ''long'' and ''short'' (tensile) fatigue cracks are discussed. It is demonstrated that this phenomenon offers a useful tool for quickly obtaining estimates of fatigue crack growth threshold while minimizing some of the uncertainties inherent in the conventional (load-shedding) procedures. Furthermore, the initiation of cracks from notches subject to remote compression is shown to offer some valuable insights into the growth and closure behavior of physically-small (tensile) cracks. The significance and limitations of the compression method are more » described. « less