Experimental investigation of the effect of the mould thermal expansion on the development of internal stresses during carbon fibre composite processing

The influence of the mould material on the build-up of internal stresses during autoclave cure of carbon fibre composites was investigated using embedded optical fibre Bragg gratings. Unidirectional and cross-ply laminates were cured on four flat moulds: aluminium, steel, carbon composite and carbon foam. From the beginning of cure, the fibres were strained by contact with the expanding mould. The strain increased with the mould thermal expansion and autoclave pressure. As a result, large residual strains were found in the longitudinal direction for the samples cured on aluminium or steel moulds, whereas the samples cured on carbon-based moulds exhibited almost no strain after cooling-down.