Crack Closure and Propagation Studies to Determine the Effects of Simple Load Interaction

Crack closure and fatigue crack growth experiments were performed on centrally notched specimens of 6063-T6 Al-alloy under single overload and block loading conditions. Using crack closure data, values of effective stress range ratio (U) were found. Assuming that the crack closure phenomenon is responsible for transient behavior of fatigue crack growth rate (FCGR), the FCGR behavior during load interaction was predicted using a constant amplitude crack propagation description in conjunction with the experimentally measured U-values. On comparing predicted FCGR with those found experimentally, it was observed that the predicted FCGR always agrees with the trend of experimental FCGR behavior and provides either exact or conservative estimates of the FCGR.