The effect of water on the fracture surface energy of fiber‐reinforced composite materials

Abstract The effect of absorbed water on the fracture surface energy of both glass and graphite fiber unidirectional epoxy composites has been studied. The fracture energy parallel to the fiber direction was measured by the double torsion technique. Water was absorbed at 70°C while the sample was subject to an external tensile stress both parallel and perpendicular to the fiber direction. No degradation of fracture surface energy was measured for specimens stressed and immersed in water at 70°C for up to 1000 h. The fracture surface energy for the glass composite was greater than for the graphite composite, which was attributed to fiber pull‐out in the case of the glass composite.