The multifarious plastic zones in front of a crack

Abstract

Since there is a stress concentration at the tip of a crack, plastic deformation must take place so that there will be a plastic zone whose size depends on the yield stress of the material. As a result the stress concentration disappears and the crack loses its potential to propagate. To show how does the dislocation-free zone develop in the case of Mode II or III, computer simulations were performed and it was shown that the dislocations actually collect at a distance from the crack tip while the stress intensity factor at the crack tip decreases. So the dislocation-free zone is large to begin with and gradually decreases. Only when the stress intensity factor at the crack tip becomes zero does the dislocation-free zone disappear. So the plastic zone can be developed in many different ways even in Mode II or III. For Mode I there are very few studies because of the complexity of the calculations. Their work showed that the plastic zone depends on the availability of slip systems and also on the order of emission of dislocations from the crack tip. The plastic zone can be saturated with dislocations (when no more dislocations can be emitted evenmore » without any critical stress intensity factor for dislocation emission) and yet the stress intensity factor at the crack tip is still not zero. A dislocation-free zone exists if there is a sufficiently large critical stress intensity factor for dislocation emission. The shape of the dislocation-free zone is similar to that of the plastic zone. These and other findings will be discussed here.« less