On the nature of abnormalities in the structural mechanical behavior of glassy polymers

Literature data on abnormalities in the mechanical behavior (stress relaxation in the initial section of the stress-strain (compression) diagram, stress growth under isothermal heating, a low-temperature contribution to the temperature-induced strain recovery of deformed polymer glasses, a soft compliant phase upon the tensile drawing of a glassy polymer revealed by dynamic mechanical tests) and in the thermophysical behavior (accumulation of internal energy at early stages of deformation and an exothermic DSC peak below the glass transition temperature) of the deformed glassy polymers are considered. The above abnormalities can be explained taking into account two fundamental features of amorphous polymers, first, the inhomogeneous character of inelastic deformation in glassy polymers, which leads to the development of discrete regions of plastically deformed material in the initial polymer (shear bands and/or crazes), and, second, a marked decrease in Tg of highly dispersed oriented material filling both shear bands and crazes.