Relation of Interfacial Adhesion to Residual Stress in Carbon Fiber/Epoxy Composites

Abstract

Two types of carbon fiber, one with surface treatment and one without surface treatment, were used to fabricate carbon fiber-reinforced epoxy composites. The relation between the degree of fiber-matrix adhesion and the thermal residual stress developed in the composite was examined. The adhesion for treated and untreated fiber was compared by the interlaminar shear strength of unidirectional laminates; the thermal residual stress was compared by the curvature of unsymmetric laminated beams. The higher degree of adhesion offered by the surface treated fiber resulted in the development of higher residual stress (and strain) in the composite. Transverse ply cracking was examined as a possible cause of the different curvature development in control and experimental unsymmetric beams, but it was found that cracking did not occur. An alternative explanation based on relative displacement at the fiber-matrix interface is described.