Aging in glasses subjected to large stresses and deformations

Abstract

Physical aging studies near the conventional glass transition temperature T g were made using a model epoxy glass. Non-linear viscoelastic responses were measured after quenching the samples from above T g to below it. The physical aging response in creep in simple extension was studied as a function of stress magnitude and in stress relaxation in torsion as a function of deformation magnitude. In each test the time, t ∗ , for the aging time shift factor to approach a constant value was determined and found to be independent of the stress or deformation magnitude. The torsional experiments were performed in a torsional dilatometer and the volume recovery response during the physical aging experiment was measured in addition to the torque response. It was found that the underlying volume recovery kinetics were not changed by the mechanical stimuli, i.e. were independent of the applied deformation. These results are interpreted to mean that large mechanical stimuli do not alter the underlying thermodynamic state of the glass and aging is not ‘erased’ by the large stresses or deformations.