Now that combinative part must be stress convergence phenomenon, and only stress convergence is large enough, so at interface edge there will be more obvious plastic region appearing to combinative part cusp putting in plastic yield state. 既然结合部位会出现应力集中现象,只要应力集中足够大,那么在界面端就会出现较为明显的塑性区,使得结合部尖端进入塑性屈服状态。