Direct Observations of Crack-Tip Dislocation Behavior During Tensile and Cyclic Deformation

摘要

Direct observations have been made of the emission and distribution of dislocations at the crack tip of propagating cracks in various metals during tensile and cyclic deformation in an electron microscope. The results show a number of new findings regarding the dislocation behavior near the crack tip and its relationship to the propagation of cracks. Depending on the loading geometry, it was possible to observe the propagation of shear cracks of mode III type as well as tensile cracks of mode I type. Some of the observations were made using a video recording system. For shear cracks of mode III type, the crack tip generated screw dislocations on planes which were coplanar with the cracks. The dislocations were generally in the form of an inverse pileup but a dislocation-free zone was present near the crack tip. For tensile cracks of mode I type, edge dislocations were generated at the crack tip on planes which were inclined to crack. As the dislocations were emitted, the crack tip was blunted and crack propagation ceased. (ERA citation 07:050836)