IN-SITU OBSERVATIONS IN SEM OF DEGRADATION OF GRAPHITE-EPOXY COMPOSITE-MATERIALS DUE TO SEAWATER IMMERSION

The effect of immersion in seawater on the mechanical properties of three graphite/epoxy composite materials has been studied. The transverse tensile strength was found to be reduced by 17% in one of the systems with essentially no change in the other two systems studied. Direct observation of fracture in the SEM as well as microindentation measurements of the interfacial shear strength have been used to explain these observations. The 17% decrease in transverse tensile strength was associated with degradation of the interfacial strength, resulting in a change in the fracture mechanism from primarily matrix cracking to interfacial failure. Little difference was found in the behavior of composites immersed in distilled water and in seawater at ambient pressure or seawater at 20.7 MPa pressure.