The Effect of Load Reduction Scheme on Crack Closure in the Near-Threshold Regime

摘要

Three-dimensional elastic-plastic finite element analyses were conducted to model fatigue crack growth in an M(T) specimen. Variable amplitude loading with a continual load reduction was used to simulate the load history associated with fatigue crack growth threshold measurement. Load reductions with both constant load ratio R and constant maximum stress intensity K_(max) were used. Results indicated that load reduction with constant R generated a plastic wake such that remote crack opening occurred during loading, with the crack front opening prior to a region remote to the crack front. The last region to open was located at the point at which the load reduction originally began, and at the free surface. In contrast, for load reduction with constant K_(max), the crack front was the last to open. The results also indicated the crack opening process is three-dimensional in nature, with regions in the interior opening prior to regions near the free surface.