Yielding behaviour in model epoxy thermosets - I. Effect of strain rate and composition

Yielding behaviour was investigated in two series of epoxy networks where the molecular architecture (crosslink density) was varied without any significant chemical changes in the structure. The DGEBA-based networks cured with aromatic amines had higher yield stresses than related networks cured with aliphatic amines, due to differences in the rigidity of the backbone. In each series, the yield stress was also found to rise with increased crosslinking. This may be caused by the increased constraint of the crosslinks on the molecular segments involved in the yielding process. The Eyring equation was found to satisfactorily describe the dependence of the yield stress on the strain rate. Surprisingly, the calculated volume of the flow unit was independent of both the crosslink density and the nature of the amine. (C) 1998 Elsevier Science Ltd. All rights reserved.