Axial compressive failure of glass-fibre polyester composites under superposed hydrostatic pressure: influence of fibre bundle size

Abstract

The axial compressive strengths of three 0·52 V f glass-fibre/polyester pultrusions were determined under superposed hydrostatic pressures extending to 300 MPa. Atmospheric strengths were in the range 380–790 MPa, and all materials showed a strong, about 3, pressure-dependence. Kinking of fibre bundles or sub-bundles preceded fracture in all materials at all pressures, but failure to detect non-propagating transverse cracks, which allow such groups of fibres to act in unison, indicates that bundle-debonding controlled the critical mechanism of failure. The effects of shape, size, and eccentricity of the bundles on buckling and debonding are considered. It is tentatively concluded that the critical parameter is the transverse tensile strain of the resin, ϵ 1 , causing bundles (rather than individual fibres) to debond. The pressure-dependence of the compressive strength is well predicted by the ϵ 1 criterion. To obtain fair correlations with the measured values, the bundle-bundle decohesion strengths would have to be to the order of 223 MPa, rather than approximately 50–100 MPa estimated for the fibre-fibre debond strengths.