Elastic energy balance and entropy elasticity

The strain energy released during shape recovery at Ti is obtained as  

Although it is small, some strain energy is also released upon removal of the strain at T  

Two important properties of SMP, i.e., shape retention and shape recovery, are obtained as follow  

In the rubbery state, a change in length, L, does not cause a change in internal energy [AU = 0). Therefore, the first law of thermodynamics states that heat, Q, is evolved during stretching  

The entropy force is weak. However, it is strong enough to cause a retraction in the liquid state when the applied stress is removed [18]. When the work done by the internal forces is balanced by the work done by the external forces producing the deformation, the total work, W, done for uniaxial drawing is obtained as  

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