Dislocation emission and dynamics under the stress singularity at the crack tip and its application to the dynamic loading effect on fracture toughness

In previous work, computer simulation of dislocation emission and motion was carried out considering the stress singularity near the crack tip. It was found that there is a region in which no dislocation exists along the slip plane near the stressed source, namely, a dislocation free zone (DFZ), and that there is an inverse pileup of dislocations against the tip of this DFZ. A formula was obtained correlating the maximum dislocation density with the DFZ length. Based on those results, an evaluation has now been attempted for fracture toughness within the brittle-ductile transition range of steel. The effect of dynamic loading on the fracture toughness and trigger point observed in the experimental results reported in the literature is explained.