Can I vary temperature with viscoelastic materials?

I seem to have built a viscoelastic material that exhibits stress relaxation with time *when the material is at glassy transition temperature*. If I move above or below that temperature and input a constant load but at varying times (1,10,100 and 1000s) I get the same answer every time.

Have I done something wrong or is this just a limitation of SW?

I really want to vary temperature in an assembly which will in turn vary the loading on several viscoelastic materials. I assumed this was possible in SW but am I mistaken?