Measurements of Residual Stress in Carbon Fibre Composite Materials Using X-Ray Diffraction

Abstract

The presence of thermal residual stresses in cured carbon fibre composites is well known and can lead to mechanical failure. A non-destructive X-ray diffraction technique which allows the six components of the threedimensional strain tensor to be determined was used to investigate carbon fibre composite materials. Measurements were made on unidirectional composites containing small metal particles as a filler, because neither the carbon fibres nor the resin matrix give suitable high angle Bragg reflexions. Significant shear strains were measured in addition to principal compressive strains. Ancillary experiments were performed on particles in resin only and whilst applying strain to the composite parallel to the ’fibres. The latter enables the strain in the metal particles to be related to that in the bulk composite.