The Effect of Aging in Water on the Strength of Fiber-Polymer Systems

Abstract The effect of the exposure time in water on the adhesive strength of fiber/resin systems was studied. To this end, the adhesive strength of single-fiber/matrix systems was measured. Such a system simulates the unit cell of a fiber-reinforced composite. The resin was an epoxy (DGEBA-based) polymer. The substrate used consisted of boron fibers, a steel wire and glass fibers. The samples were kept in water for a period of 1-280 days at room temperature and the adhesive strength was measured also at room temperature. The water absorption of the resin and the impregnated strand produced on the basis of the glass fibers and the resin studied and also the physico-mechanical characteristics of the impregnated strand were studied at the same time. The samples used to determine the adhesive strength were kept in such a contact with water that the latter could penetrate into some of them only at the interface and into the others at the interface and through the resin layer. It was found that the adhesive strength decreases with increasing amount of water absorbed. On the basis of the results obtained it was concluded that the principal factor that determines the loss in adhesive strength during the aging of the systems in water is the plasticization of the epoxy resin by water.