| This work is part of the project of "mechanical simulation and experimental investigation of the nucleation of nano-cracks" supported by the National Natural Science Foundation of China (Grant No. 10272020). The purpose is to investigate the mechanisms of crack initiation and propagation. This thesis is concentrated on TEM observation and computer simulation of dislocation emission from a crack.TEM observation of dislocation emission was carried out on an austenitic stainless steel. It is found that defects such as cracks and dislocations exist in the materials. Upon loading, dislocations were emitted out from crack tips along multiple directions. When the dislocation emission process stopped there exists a dislocation-free zone in front of the crack tip, and the emitted dislocations are inversely piled-up outside the dislocation-free zone. Increasing the applied load, micro-cracks may initiate inside the dislocation-free zone as a result of breakdown of atomic bonds and crack propagation is achieved by coalescence of the micro-cracks and the main crack. The emitted dislocations may pile-up at... |
