Mechanics of Time-Dependent Materials

, Volume 15, Issue 3, pp 255–275 | Cite as

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

  • Lorenzo BardellaEmail author
  • Andrea Belleri


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 \(\dot{\varepsilon} _{0} \approx 1.\mathrm{E}{-}6~\mathrm{s}^{-1}\), 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.

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.


Mechanical characterization Epoxy resins Strength Viscoelasticity Viscoplasticity Instability 


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© Springer Science+Business Media, B. V. 2011

Authors and Affiliations

  1. 1.DICATAUniversity of BresciaBresciaItaly
  2. 2.Department of Design and TechnologyUniversity of BergamoDalmine (BG)Italy

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