Structural plastic microbuckling and compressive strength of long-fibre composite materials

Abstract

It is now well established that the axial compressive strength of organic long-fibre composites is limited by the development of a local instability of the fibres. This so called microbuckling depends strongly on the coupling of the fibre initial geometric imperfection with the resin non-linear shear behaviour. In addition, it has been demonstrated experimentally that failure strains also depend on some structural parameters at the ply scale, the effect of which is less well known. We have been investigating this structure effect for several years from both experimental and theoretical points of view. In the present paper a model is proposed that is able to account for both local and structural parameters, with reasonable computation amounts. Then, by comparing predictions from this model with experiments, we demonstrate the necessity of accounting for the structure effect when designing composites against compression. Eventually, the last parameter still to be determined is the fibre initial imperfection which is thought to result from a fibre instability occuring during cure. A viscoelastic micromechanical model is presented here which very well captures the microbuckling of a single fibre induced by the resin thermosetting shrinkage.