Two features of the uniaxial compression of a glassy epoxy resin: the yield stress rate-dependence and the volumetric instability

摘要

We report the results of uniaxial compressive tests on a DGEBA epoxy resin at room temperature, well below its glass transition. We first focus on the strength, defined as the stress value corresponding to either a maximum or a flattening of the stress-strain curve, which, for this polymer, may be taken to be coincident with the yield stress, as often assumed for many thermosets. Within the strain rate range (1.E−6 s−1, 2.E−3 s−1) we confirm the linear trend relating the logarithm of the strain rate to the yield stress, as already been observed by other investigators even for the same epoxy resin; instead, at strain rates below [(e)dot] ₀ » 1.E-6 s-1dot{varepsilon} _{0} approx 1.mathrm{E}{-}6~mathrm{s}^{-1}, we found a negligible rate-dependence, as our data indicate a lowest limit of the yield stress, of about 87 MPa. On the basis of these results, we propose how to extend to the viscoplastic regime of deformation a nonlinear viscoelastic model previously put forward.