Accelerated Threshold Fatigue Crack Growth Effect - Powder Metallurgy Aluminum Alloy

INTRODUCTION In cases where fatigue lives primarily depend on the early stages of crack growth, it is critical to understand the FCG characteristics in the near threshold regime, defined schematically in Figure 1. Considerable research has shown that an acceleration in near threshold FCG rates (da/dN) occurs with increasing stress ratio due to a reduction in crack closure (Newman and Elber [1]). However, research has suggested that crack closure does not account for all stress ratio effects when R ranges from 0.5 to 0.95, and for K,x greater than 0.4 Kic (Gan and Weertman [2] and Beevers [3]). This work suggests that near threshold FCG can be influenced by other crack-tip damage mechanisms (K,x effects) that are not related to crack closure. For ingot metallurgy aluminum and titanium alloys, relatively small near threshold K,x effects have been observed during closure free FCG [3]. Others have concluded that highly accelerated near threshold FCG rates during constantK, x testing of l