Three techniques of interfacial bond strength estimation from direct observation of crack initiation and propagation in polymer-fibre systems

Three techniques of bond strength determination in micromechanical tests-fibre strain profile analysis by means of Raman spectroscopy, "kink" force determination in a traditional pull-out test, and crack length monitoring in a microbond test-were used for investigation of interfacial debonding in epoxy-glass fibre and epoxy-aramid fibre systems. Crack propagation was characterised by local interfacial parameters-critical energy release rate, G(ic), and ultimate interfacial shear strength (IFSS), tau (ult). The comparison of the results showed good agreement both between different techniques and between stress-based and energy-based failure criteria. Sizing of glass fibres caused more pronounced variations in the IFSS than for aramid fibres due to different interfacial failure patterns. The strength of "real" epoxy-glass composites with sized and unsized fibres correlates well with the bond strength determined from the micromechanical tests. (C) 2001 Elsevier Science Ltd. All rights reserved.