The effects of unequal compressive/tensile moduli of composites

This paper investigates the effects of unequal compressive and tensile moduli of carbon fibre reinforced plastic (CFRP) composites. The basic assumption is based on the statistics that the compressive modulus is a fraction lower than the tensile modulus. Data evaluated by Finite Element Analysis (FEA) model, Classical Laminate Theory (CLT) model, and experiment are used to investigate these effects. The terms of compressive modulus are successfully introduced into the Tsai-Wu failure criterion for the production of failure envelops, into the Classical Beam Theory (CBT) and CLT for the investigation of flexural behaviour as well as the fibre microbuckling model for the analysis of compressive failure. The study shows that the failure criteria shift from stress domain to strain domain when the compressive modulus is considered, and the strain dominated failure criteria could generally provide more accurate prediction in composite material. Therefore it is proposed to apply strain dominated failure criteria for composite design, testing and certificate.