Modelling the thermomechanical behaviour of shape memory polymer materials

The increasing applications of smart structures in technology development have led to a wide variety of new high performance materials, especially smart polymers. In the present work, a uniaxial model for shape memory polymer (SMP) is analyzed and a consistent form of the constitutive law is proposed. The coefficient of thermal expansion is expressed using the rule of mixtures approach. In this study, a comparison is made between thermal strains computed by using the analogous rule of mixture equation and the empirical relation that has been stated on the basis of experimental findings. The inconsistency in the computation of coefficient of thermal expansion is addressed. Furthermore, the consistent form of the stored strain and thermal strain expressions are also presented using fourth order Runge-Kutta method. A noteworthy difference is observed due to change in temperature. Moreover, the difference between the proposed analytical solutions with the empirical relation is brought out. Finally, the consistent form of the constitutive model with modified CTE and strain expressions for the SMP is presented.