In situ measurements of through-the-thickness strains during processing of AS4/8552 composite

A novel approach has been developed to measure in situ the through-the-thickness strains during processing of epoxy composites. The technique captures the thermal expansion during the heating stages, the laminate consolidation throughout the cure process, and also the cure shrinkage. The tests were performed on 45 mm × 45 mm × 4 mm samples, for both unidirectional and cross-ply laminates. A ply pull-out technique was used to determine the position of the gel point of the AS4–8552 composite system for various curing temperatures. The relationship between the chemical shrinkage and the degree of cure was deduced from a cure kinetics model. Finally the relative contributions of cure shrinkage, thermal expansion and consolidation to the through-thickness strain were distinguished.