Experimental investigation of creep-crack-tip deformation using moiré interferometry

High-temperature moiré interferometry was applied to obtain full-field creep-crack-tip displacements of a three-point bend Al 2024-T4 specimen uner constant temperature of 200°C up to 720 hr.C^* was evaluated by the moiré data obtained at discrete time intervals. Test results indicate that under steady-state creep condition, the creepcrack-tipv-displacement rate agrees with the asymptotic solution based on theC^* integral. However, no creeping behavior was observed for the crack-tipu-displacement field aftert=276 hr. This discrepancy may be due to the initial large creep-crack-tip blunting and cavitation damage which alter the creep-crack-tip singular field such that theC^* integral is no longer applicable to characterize the steady-state creep-crack-tip field. Postmortem studies of the tested specimen also revealed transgranular fracture path with the ordered grain boundaries perpendicular to the crack line, which may relate to the existence of the substantial crack-tip blunting and noncreeping behavior of theu-displacement field, i.e., the size and shape of material grain boundaries play an important role in the crack-tip-creeping behavior of the material.Paper was preseted at the 1991 SEM Spring Conference on Experimental Mechanics held in Milwaukee, WI on June 9–13.