Influence of Fiber-Matrix Adhesion on Mechanical Properties of Graphite/Epoxy Composites: I. Tensile, Flexure, and Fatigue Properties

Abstract

Tension, flexure and fatigue tests were carried out using the graphite/epoxy composites with two different fiber surface conditions to identify the effects of fiber-matrix adhesion on the mechanical properties of composites in conjunction with the variation of fiber volume fraction. Only a slight increase in longitudinal tensile and flexural strengths as well as strains-to-failure is obtained with the substantially increased interfacial shear strength, while the longitudinal tensile and flexural moduli are nearly the same. However, a significant increase in transverse tensile and flexural strengths or strains-to-failure is accompanied with the improvement of fiber-matrix adhesion, though the transverse tensile and flexural moduli are basically independent of the variation of fiber-matrix adhesion. Under tension-tension fatigue loading, the composites with a strong fiber-matrix adhesion have a clearly longer fatigue life at high applied fatigue stresses, while at low applied fatigue stresses the effect of fiber-matrix adhesion on the fatigue life of a composite becomes less pronounced. It was found that the mechanical properties of a composite with a high fiber volume fraction are more sensitive to the change of fiber-matrix adhesion than those with a low fiber volume fraction.