2 Values Of Young's Modulus Of Elasticity

I am currently trying to model a material (an S.M.A) with 2 values of Young’s Modulus of Elasticity at 2 different temperatures:  E=31 KN/mm^2 at T= -5C and E=79 KN/mm^2 at T= +25C.  I have a 3-D component set up to which I apply a sufficiently large force to take the material past its yield point, so that when I remove this force the component stays in its displaced shape (or very near to it).  This is carried out at a temperature of T= -5now want to apply a temperature of T= +25C.  This change in temperature and E should make the component want to revert back to its original position, but it doesn’t.  Is this a limitation of ANSYS, that a material can only have one value or each property?  Has anyone else had this problem, or can anyone offer any advice?  Thank you very much.
By the way I have the 2 values of E and yield stress set up as one material model and ANYSYS correctly plots me a graph showing this data.  Any ideas?

ADAM COOKE
STUDENT
SUSSEX UNIVERSITY
ENGLAND