THE NONLINEAR VISCOELASTIC RESPONSE AND APPARENT REJUVENATION OF AN EPOXY GLASS

Following a quench from above the glass transition temperature Tgto below, it is known that the mechanical response evolves (physical aging) and can be represented by a time-aging time superposition principle. The value of the aging time shift factor ateis known to depend on the magnitude of the applied stress or strain. Here the viscoelastic response of a material undergoing physical aging and subjected to a single large strain “probe” (step deformation followed by a step to zero deformation) followed by small strain probes is analyzed. It was found that a Bernstein, Kearsley, and Zapas (BKZ) constitutive equation which includes an aging clock that depends upon the deformation magnitude describes the response. The results are discussed and related to the apparent “rejuvenation” described by Struik in similar thermomechanical histories. © 1986, American Institute of Physics. All rights reserved.