Single-fibre Broutman test:: fibre-matrix interface transverse debonding

The single-fibre Broutman test was used to study the fibre-matrix interface debonding behaviour when subjected to a transverse tensile stress. During testing, damage was detected using both visual observation under polarized light and acoustic emission (AE) monitoring. Separation of failure mechanisms, based on AE events, was performed using time domain parameters (amplitude and event width) and fast Fourier transform (FFT) frequency spectra of the AE waveforms. The latter can be considered as a fingerprint allowing to discriminate fibre failure, matrix cracking, fibre-matrix interface debonding, friction and 'parasite noise'. Stresses in the specimens were evaluated using a two-dimensional finite element model (FEM) and monochromatic photoelasticity was used to verify the simulated stress distribution. Two failure mechanisms appeared to be in competition in the Broutman test: fibre failure under compressive stresses and fibre-matrix interface debonding under transverse tensile stresses. For systems in which the interfacial adhesion is not so 'good', like glass fibre-polyester systems for instance, fibre-matrix debonding was observed, and the progression of the debonding front with the interfacial transverse stress was recorded. Thermal stresses are also discussed, and a FEM simulation shows that they encourage fibre failure under compressive stresses. (C) 1999 Elsevier Science Ltd. All rights reserved.