THE OPPOSITE SIGN DISLOCATIONS AT A CRACK TIP AND THE IMAGE FORCE THEORY OF DISLOCATION-FREE ZONE
裂纹顶端的异号位错和无位错区的象力理论

The dislocation distribution function in the plastic zone at a crack tip is calculated with the help of a modified BCS-type crack model. It is found that opposite sign dislocations appear on the slip plane immediately ahead of the crack tip. These negative dislocations seem to enter the crack tip and blunt it, resulting in a dislocation-free zone at the crack tip. The image force theory of the formation of dislocation-free zone is discussed.