Explanation

deformation that cannot be restored after removing external forces, also known as plastic deformation. It is caused by crystal slip and twinning. The movement of dislocation in the slip plane will cause the crystal to slip, because the upper and lower crystal halves of the area swept by dislocation will produce relative displacement along the slip direction, thus generating a plastic shear strain. In short, as long as the external force exceeds the yield stress and can make the dislocation move, plastic deformation can be generated. For single crystals, the shear stress is greater than the critical resolved shear stress r. Can produce plastic deformation. For engineering materials, when the stress is greater than yield strength, macro plastic deformation can occur. Sometimes, when the stress is slightly lower than the yield strength, the dislocation in the local area can also move, resulting in micro plastic deformation. During mechanical twinning, the two parts of crystal will rotate to form mirror symmetry, and shear plastic deformation will occur. The deformation caused by twinning only accounts for a small part of the total plastic deformation, but twinning can change the orientation of some crystal relative to the tensile axis, making the new slip system start to slip, so that plastic deformation can continue to occur. During high temperature creep, plastic deformation can also be generated through grain boundary slip and vacancy diffusion. When the martensitic transformation or the second phase precipitation occurs, if the internal stress is large enough, the proliferation and movement of dislocation can be induced around, resulting in microscopic plastic deformation.

Classification