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 mechanis
ms, based on AE events, was performed using time domain parameters (amplitu
de and event width) and fast Fourier transform (FFT) frequency spectra of t
he AE waveforms. The latter can be considered as a fingerprint allowing to
discriminate fibre failure, matrix cracking, fibre-matrix interface debondi
ng, friction and 'parasite noise'. Stresses in the specimens were evaluated
using a two-dimensional finite element model (FEM) and monochromatic photo
elasticity 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 debondi
ng 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 f
ailure under compressive stresses. (C) 1999 Elsevier Science Ltd. All right
s reserved.