Deterioration in Ductility of Glassy Poly (methyl methacrylate) during Low-Strain-Rate Extension

Abstract

Stress-strain curves obtained in step-extension tests on glassy poly (methyl methacrylate) were compared with S-S curves obtained at constant extension rates. It was found that ductility of the polymer decreased considerably when the polymer had been subjected to stretching at very low strain rates prior to the higherrate step extension. The fracture envelopes in the diagram of S-S curves of glassy PMMA also confirmed the deterioration in the ductility of the polymer during low-strain-rate extension. The decrease in ductility was closely associated with the brittle to ductile transition, i. e. the initiation of plastic flow, in the polymer. The reason for the decrease in ductility is discussed in terms of the strain-rate dependence of the magnitude of activation volume in plastic flow in the glassy polymer.