The most common shape-memory polymers are those in which the shape-recovery is thermally-induced. A body made from such a material may be subjected to large deformations at an elevated temperature above its glass transition temperature V_g Cooling the deformed body to a temperature below V_g under ac tive kinematical constraints fixes the deformed shape of the body. The original shape of the body may be recovered if the material is heated back to a temperature above V_g without the kinematical constraints. This phenomenon is known as the shape-memory effect. If the shape recovery is partially constrained, the ma terial exerts a recovery force and the phenomenon is known as constrained-recovery.
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