Thermodynamic investigation of yield-stress models for amorphous polymers

Abstract

A thermodynamic study of the yield process in amorphous polymers is proposed to investigate four yield theories: the Eyring model and its linearized form, the cooperative model and the Argon model. For a poly(methyl methacrylate) (PMMA) and a polycarbonate (PC), the corresponding apparent activation volumes and apparent activation energies are calculated and compared for a wide range of temperatures and strain rates. For the cooperative model, we show that the secondary molecular relaxation is a key parameter in the explanation of the specific mechanical behaviour of glassy polymers at low temperatures and at high strain rates. For the three other models, thermodynamic inconstancies were found and these are discussed.