Strength of unidirectional composites under high hydrostatic pressures

The dependence of the strength properties of two unidirectional fibrous composites oil high (up to 500 MPa) hydrostatic pressure has been studied experimentally. Ring specimens of epoxy carbon- and glass-fiber reinforced plastics were tested in tension using half-disk devices. The tensile strength in the reinforcement direction increased with increase in the pressure lip to 300 MPa. However, at a further increase in the pressure, this strength decreased. It was found that the failure mode of unidirectional Composites depends oil the magnitude of hydrostatic pressure. The failure shapes differed in the location of the failure zone and in the relative extent of longitudinal cracks in the specimens. At atmospheric pressure, the failure zone covered practically the whole volume of the specimens. With increased pressure, the failure zone became localized. At the highest pressures investigated, the failure was accompanied by the formation of a single crack across the reinforcement direction.