The non-coplanar coalescence of interacting defects in fatigue

摘要

Defects in real structures frequently have complex shapes. The present work examines complex defects which result from the interaction of adjacent coplanar semi- elliptical cracks. Attention is focused on fatigue growth leading to coalescence and the formation of a coplanar single defect with a re-entrant sector. An experimental study investigated the fatigue crack path on the free surface. The study found that the deviations from the straight crack path determine the size of the re-entrant sector and whether coalescence occurs on the surface or sub-surface. Surface coalescence occurs by a shear mechanism resulting in a step in the coalesced crack front. A numerical line spring analysis based on the concept introduced by Rice and Levy and extended by Parks and White to include Mode II and III component, has been used to investigate the effect of coalescence in re-entrant sector on the crack tip parameters. The presence of a step in the re-entrant sector introduces a Mode III component and reduces amplified values of Mode I stress intensity factor, which is a feature of coplanar coalescence. The study concludes with discussion of the significance of non- coplanar coalescence on catastrophic brittle failure.