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 (epsilon) over dot(0) approximate to 1.E-6 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. Secondarily, within the viscoelastic range, at a stress level significantly lower than the yield stress, our measurements show a mild volumetric instability, allowed by the free lateral expansion, not ascribable to any macroscopic structural effect; such a behaviour has never been reported in the literature, to the best of our knowledge.

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

BELLERI, Andrea
2011-01-01

Abstract

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 (epsilon) over dot(0) approximate to 1.E-6 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. Secondarily, within the viscoelastic range, at a stress level significantly lower than the yield stress, our measurements show a mild volumetric instability, allowed by the free lateral expansion, not ascribable to any macroscopic structural effect; such a behaviour has never been reported in the literature, to the best of our knowledge.
journal article - articolo
2011
Bardella, Lorenzo; Belleri, Andrea
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10446/28179
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