1989 年 38 巻 434 号 p. 1329-1335
An investigation has been carried out concerning the influence of water absorption on the tensile and fatigue properties of angle-ply composites of Kevlar 49 (Dupont)/epoxy and a Technola (HM50, Teijin)/epoxy. The influence of water on the fracture mechanism was observed by a SEM and an acoustic microscope.
The weight gain of both composites immersed in distilled water at 80°C leveled off at about 2% after two months. For the Kevlar 49 composites water absorption increased tensile strength as well as fracture strain, while the tensile strength of the HM50 composites was decreased by water absorption. For both composites the specimens in water at room temperature and in hot water exhibited a shorter fatigue life than that in air. Water absorption causes plasticization of epoxy resin, thereby reducing interlaminar residual stress of laminates. Also water absorption lowers the interfacial strength between fiber and resin as well as lateral strength of fibers, thereby reducing intra-and interlaminar strength of laminates. These factors influence respectively the tensile and fatigue strength of laminates in water. We also point out the usefulness of a scanning acoustic microscope to examine the internal damage of the composites.