Counter-intuitive effect of the degree of cure of epoxy resins on the compressive strength of continuous fibre composites
Vincent Kéryvin, P.-Y. Méchin, Emmanuel Fabing, Isabelle Pillin, Kylian Mahé-Flahaut, Antoine Le Palabe
Abstract
It has been observed that some epoxy resins exhibit the greatest elastic stiffness when not fully cured. In this study, this counter-intuitive resin behaviour (stiffness) is shown to be reflected in the compressive strength of associated epoxy fibre composites. A reduction of up to 30% in both properties can be observed when going from incomplete conversion to complete cure. The Budiansky and Fleck compressive failure criterion (Budiansky and Fleck, 1993) is, in this study, proven to be both qualitative and quantitative in its relevance for describing the reduction in compressive strength. This study is of particular importance to engineers and manufacturers of composites, as the conventional belief is that optimum performance is achieved with a complete cure. • Some thermosets have lower stiffness when fully cured than when partially cured. • Associated fibre composites have lower axial compressive strength when fully cured. • A compressive failure criterion elucidates the propagation from resin to composite.