Structural relationship between thermomechanical history and strength of polymeric solids

Ultimate properties in polymeric solids strongly depend on thermomechanical history. We have shown that the polymer structure which depends on thermomechanical history can be quantitatively described by the relative amounts of enthalpy and entropy. The excess enthalpy decreases upon annealing and increases under the tensile stress. The increase in excess enthalpy reduces the relaxation time; thus a local brittle-to-ductile transition may be induced by stress concentration. It follows that in a well-annealed material, this transition is more difficult to induce. Effects of molecular weight and orientation are also discussed in terms of dissipation of strain energy as the condition required for the strength of polymeric solids.