Mechanical properties of thermosets
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The tensile properties of a DGEBA (diglycidylether of bisphenol A)-norbornene anhydride network (Tg≈130±5 °C), were studied in the range (220 K-Tg); 4×10−4 to 14×10−3S−1. The viscoelastic spectrum (1 Hz) reveals a low β transition at 220 K. The bulk modulus is practically constant between 200 K andTg — 20 K. The Poisson's ratio increases very slowly untilTg — 30 K. Then it increases rapidly to reach its asymptotic value (0.5) near toTg. The tensile (E) and shear (G) moduli display the classical behaviour linked to viscoelasticity. Plastic yielding occurs atT ≥ 80 °C, the elongation at yield is almost temperature and strain rate independent (G3y = 0.035), whereas the yield stress obeys Kambour's relationship: σy = 1.1 (Tg —T) and Eyring's law (activation volume = 914cm3mol−1). Physical ageing at 120 °C strongly affects the yield stress and the ductility. The maximum draw ratio, obtained atT ≥Tg, is ΛRC = 1.35, which seems to be consistent with the network's crosslink density.
KeywordsPolymer Mechanical Property Ductility Anhydride Tensile Property
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