The Influence of Water on the Mechanical Properties and Fatigue Strength of Angle-Ply Carbon/Epoxy Composites

An investigation has been carried out concerning the effect of water absorption on the mechanical properties and fatigue strength of ±45° angle-ply carbon/epoxy composites, i.e., 130°C cure-type composites T-1/347, and 180°C cure-type MM-1/982X. In both composites, water absorption lowers the strength of the interface, resulting in a decrease in the tensile strength, an elongation at the break, and besides, fatigue strength. In a higher stress region in laboratory air, cyclic loads make the temperature of a T-1/347 composite so high that plastic deformation of the matrix is enhanced and the fatigue life is shortened. In water, however, cooling effects by water circulation around specimens become predominant, so that the fatigue life increases in a higher stress region. We also pointed out the usefulness of a scanning acoustic microscope to examine the internal damage of the composites.