YIELDING BEHAVIOR IN MODEL EPOXY THERMOSETS - II - TEMPERATURE-DEPENDENCE

The temperature and strain-rate dependence of yielding in compression has been investigated for a series of model thermosets in which crossl ink density is varied without compositional change. The yield stress w as only indirectly influenced by the crosslink density through its eff ect on the molecular mobility and the glass transition temperature. Th e Eyring activation volume was relatively insensitive to changes in cr osslink density or composition but increased as the temperature was ra ised. The Robertson theory of yielding was found to give an approximat e prediction for the temperature and strain rate dependence of the yie ld stress and the adjustable molecular parameter in this theory was cl ose to the theoretical value. Neither the Argon nor the Bowden theorie s yielded significantly improved fits to the data. The use of these st ructurally related polymer systems appears to provide a very sensitive test of yielding theories. (C) 1998 Elsevier Science Ltd. All rights reserved.