Influence of fiber-matrix adhesion on mechanical properties of graphite/epoxy composites: II. Interlaminar fracture and inplane shear behavior

A comprehensive experimental study was conducted to determine the effects of fiber-matrix adhesion on Mode I and Mode II interlaminar fracture toughness, interlaminar shear strength, and inplane shear properties of the graphite/epoxy composites with different fiber volume fractions. With the improvement of fiber/matrix adhesion by fiber surface treatment and sizing, Mode I and Mode II interlaminar fracture toughness, interlaminar shear strength and inplane shear strength of the composites were clearly increased. However, the interlaminar fracture properties were not so sensitive to the variation of fiber volume fraction. Only a slight increase in the interlaminar shear strength was found when the fiber volume fraction of the graphite/epoxy composites was increased. The results also indicate that although the fiber/matrix interface can play a role in controlling the interlaminar fracture behavior to a certain extent, the improvement of interlaminar fracture toughness resulting from interfacial modification is not as great as that obtained by the use of the toughened matrices.