The Influence of Moisture and Pressure on the Mechanical Properties of a Glass-Epoxy Matrix Composite and a Graphite-Epoxy Matrix Composite

Abstract : The influence of exposure to water at ambient pressure and at elevated pressure was evaluated on the mechanical properties of a glass fiber- epoxy matrix composite and a graphite fiber-epoxy matrix composite. The mechanical properties of three different fiber orientations for each material were measured in the dry condition, after exposure to water at ambient pressure and after exposure to water at 5.9 MPa. In order to determine if the observed degradation was permanent, the mechanical properties were also measured after the absorbed water was removed. During exposure, the rate and extent of water absorption and desorption was evaluated by measuring the weight change at periodic intervals. Substantial reductions in the yield strength and ultimate strength were observed in the wet condition for the glass epoxy samples at both pressures, while the strength of the graphite epoxy composite was found to be insensitive to the water exposure. The wet strength of the glass epoxy composite was found to be independent of water pressure during absorption and upon desorption, complete recovery of the dry strength was demonstrated. Evidence of compression-induced failure was observed for the graphite-epoxy composite in the wet condition.