Mechanical properties of thermosets .1. Tensile properties of an anhydride cured epoxy

The tensile properties of a DGEBA (diglycidylether of bisphenol A)-norbornene anhydride network (T-g approximate to 130 +/- 5 degrees C), were studied in the range (220 K-T-g); 4 x 10(-4) to 14 x 10(-3) s(-1). The viscoelastic spectrum (1 Hz) reveals a low beta transition at 220 K. The bulk modulus is practically constant between 200 K and T-g-20 K. The Poisson's ratio increases very slowly until T-g-30 K. Then it increases rapidly to reach its asymptotic value (0.5) near to T-g. The tensile (E) and shear (G) moduli display the classical behaviour linked to viscoelasticity. Plastic yielding occurs at T greater than or equal to 80 degrees C, the elongation at yield is almost temperature and strain rate independent (epsilon(Y) = 0.035), whereas the yield stress obeys Kambour's relationship: sigma(y) = 1.1 (T-g-T) and Eyring's law (activation volume = 914 cm(3) mol(-1)). Physical ageing at 120 degrees C strongly affects the yield stress and the ductility. The maximum draw ratio, obtained at T greater than or equal to T-g, is Lambda(RC) = 1.35, which seems to be consistent with the network's crosslink density.