| Abstract: | Tensile experiments in polystyrene (PS) and poly(methyl methacrylate) (PMMA) conducted at constant strain rate over a wide range of pressure and temperature have shown that a brittle-to-ductile transition is induced in these amorphous polymers by the superposition of hydrostatic pressure as well as by the raise of the experimental temperature. A detailed stress–strain analysis permits explanation of the mechanism for the brittle-to-ductile transition in terms of interaction between two competing processes of plastic yielding—crazing and shear banding phenomena. The crazing and shear banding processes respond quite differently to changes of pressure or temperature, causing shifting of the brittle-to-ductile transition point to where the craze initiation stress and shear band initiation stress again become equal. The evidence that the brittle-to-ductile transition pressure becomes lower with increasing temperature refutes a previously suggested concept that the transition relates primarily to mechanical relaxation phenomena. |
