Continuous micro-indenter push-through technique for measuring interfacial shear strength of fiber composites

Abstract

This paper describes a continuous push-through, micro-indentation technique for measuring the fiber-matrix interfacial shear strength. E-glass fibers embedded perpendicular to the plane of thin polished specimens of epoxy matrix, with and without coupling agents, were indented with a micro-indenter until failure of the interface occurred and the fibers were pushed through the epoxy. The results show over 60% higher interfacial shear strength for fibers with coupling agent than for fibers without coupling agent. Average shear strength values obtained via the indentation technique are in good agreement with those obtained from the single-fiber-composite test. Absence of acoustic emission signals for debonding of the fibers coupled with no sudden drops in load vs indentation depth suggest that in this geometry the debonding is a slow, continuous process for both fiber surface treatments.