The mechanical properties of polymers are temperature dependent. The diagram shows a series of stress/strain curves for polymethyl methacrylate measured between 4C where the material is brittle and 60 C where it shows a viscous flow component to the plastic deformation. The elastic modulus (initial slope of the stress/strain curves) also

shows as strong temperature dependence. Also, the ultimate tensile strength of the polymer decreases as the temperature increases, however, the strain to fracture increases and the work done to fracture (area under the curve) also increases.

These curves were taken at a constant strain rate. In general, the material response will be strain-rate dependent. The material has a characteristic 'relaxation time' which decreases exponentially with increasing temperature and is associated with molecular motion. Strain rates that couple with this relaxation time will have the largest effect.

From: Callister, "Materials Science and Engineering,"
Wiley (1997)