Phase-stepping photoelasticity for quantifying the interfacial response in fibre composites at fibre-breaks

A phase-stepping photoelastic technique has been used to study the fragmentation of E-glass fibre and evaluate quantitatively the effect of an interphase region on interfacial shear strength at a fibre-break and hence the efficiency of the interfacial bond. To investigate the interfacial response of an E-glass fibre in the presence of a soft interphase, it was coated with an epoxy resin of lower Young's modulus and yield strength than that of the matrix resin. This enables the effect of a sizing or modified matrix region to be quantified. The micro-mechanical response in the matrix at the interface/interphase has been described in detail using contour maps of fringe order. From these, the profile of the interfacial shear stress at fibre-breaks has been calculated, which demonstrated that in this cold-cured epoxy resin a good interface formed with uncoupled and unsized E-glass. In the presence of a modified matrix or interphase region the stress transfer process was modified and the stress concentration associated with a transverse crack reduced.