In situ monitoring of the fibre strain distribution in carbon-fibre thermoplastic composites 1. Application of a tensile stress field

The distribution of residual thermal strains and the mechanical response of carbon-fibre thermoplastic composites on the application of an external tensile stress have been studied. Confocal laser Raman microscopy has been employed to monitor the Raman wavenumbers of the embedded carbon fibres, within a predefined 'window' of observation. The application of a tensile stress held on the P75/ PEEK composite induces an internal fibre stress/strain gradient as a result of progressive fibre fracture and matrix microcracking. The spread of the fibre strain distribution is primarily dependent on the magnitude of the residual thermal stresses and the level of applied stress. In cases where the optical monitoring of discontinuities, such as fibre and matrix breaks, is not possible, a statistical approach is pursued for monitoring the micromechanics of failure in these composites. (C) 1999 Elsevier Science Ltd. All rights reserved.