Platic deformation results in a permanent change of shape,meaning that after load in removed, then metal will not return to its original dimensions. This implies a permanent displacement of atoms within the crystal lattice. If a perfect crystal is assumed, this deformation could only occur by breaking all of the bonds at once between two planes of atoms and then sliding one row (or plane) of atoms over another. Based on calculations using the theoretical bond strengths, this process would result in yield strengths on the order of 10000 to 100000 MPa. These strengths are much greater than those typically observed in actual metals(100MPa); therfore, deformation must occur via a different method.

1. permanent 永久的

2. displacement 位移

3. slide滑动

4. order量级