In order to improve the ability of solving the high dimention and mass data,based on the old algorithm,a modified one with the methods of density and the best space division is presented.

Mode Ⅰ crack tip plastic zone,dislocation-free zone and their effects on crack propagation;

Dislocation emission from the crack tip,formation of dislocation-free zones,nucleation of nano-cracks and dislocation pile-ups were all observed.

A dislocation free zone(DFZ) is formed between crack tip and the inversely pileup dislocations when the dislocation emission and motion reach equilibrium.

TEM in situ tensile tests of 310 stainless steel show that a dislocation free zone (DFZ) forms after equilibrium if the displacement keeps constant after many dislocations are emitted from a crack tip.

The results show that 1)in precharged specimens,many dislocations can emit from a crack tip followed by forming a dislocation free zone(DFZ) after equilibrium:2)nanocracks nucleate preferable in DFZs;3)microcracks connect with each other,resulting in the brittle cracks,instead of blunting into voids.