How Materials are broken Every material has their own defect. Suppose that there is somthing long steel wire, like clothes hanger. If you want to cut it, maybe you are going to band it upside and downside. While you band it, what happens in the material with nano size? In the banding point(the tip) many defects are generated. We call this defects "dislocations". The dislocation is generated near the tip, especially the most in the tip. And this dislocations move to the tip. If you band over and over, you feel that banding is more hard than just conducting. Because each dislocation makes other dislocations moving hard. So to move this dislocations, It needs more force. And same time, dislocations that be more hard to move are piled up in the tip. At the end of state, piled up dislocations make material too hard to band, your force cut atoms bond and the material will break. We call it fracture.