Strain rate and temperature effects on the mechanical behaviour of epoxy mixtures with different crosslink densities

The microstructure and the flexural behaviour of two highly crosslinked epoxy mixtures have been investigated. Besides the usual α and β relaxations appearing for any epoxy mixture, an additional ω relaxation, located slightly above room temperature, was evident for the mixture with higher crosslink density. This relaxation, which seems to be related to microstructural variations originating in a free volume increase, permits us to explain the lower mechanical properties of the larger higher crosslinked mixtures in the temperature range between the β and α relaxations. Whilst at room temperature the flexural modulus did not show any significant variation upon testing rate and the strength slightly increased for both epoxy mixtures.