Measurement of (post-)curing strain development with fibre Bragg gratings

Curing shrinkage of polymer matrices is a significant source of residual strain formation in thick composite products manufactured with liquid resin infusion. The goal of this paper is to investigate the contributions of cure shrinkage and postcure to residual strain development in a thermosetting polyurethane system suitable for resin infusion of thick composites using fibre Bragg gratings. The results showed that around half of the total shrinkage that contributes to residual strain build-up is due to chemical shrinkage, whereas the other half comprises thermal contraction from the vitrification point. The postcure treatment was found to relax internal strains significantly. The strain-free temperature was found below the postcure temperature and, therefore, the postcure treatment did not induce additional chemical or thermal strains.