Tensile tests at various temperatures are conducted to detect the relationship of material strain and stress of the styrene-based shape memory polymers (SMP).The material elastic modulus and yielding limit stresses at the temperatures of 25℃

30℃

40℃ and 50℃ are determined according to the results of tensile tests.In order to describe the glass transition behavior of the styrene-based SMP

a new material parameter function is supposed based on the results of the tensile tests.The styrene-based SMP is assumed as an isotropic material

then a three-dimensional thermo-mechanical constitutive equation of SMP is developed based on Tobushi’s one-dimensional thermo-mechanical constitutive equation.In order to perform finite element analysis on SMP by using ABAQUS

a UMAT subroutine for ABAQUS is programmed with Fortran codes based on the three-dimensional constitutive equation and the new material parameter function.The shape memory thermo-mechanical process of styrene-based SMP is numerically simulated by ABAQUS coupled with the UMAT subroutine

which includes deformation at a high temperature upon loading

shape fixity due to cooling and shape recovery through heating.Numerical results show that the thermo-mechanical behavior of SMP can be well simulated by ABAQUS coupled with the UMAT subroutine.