Effect of Moisture on E-Glass/Epoxy Interfacial and Fiber Strengths

Abstract

The effect of absorbed moisture on the fiber and interfacial strengths of an epoxy reinforced with continuous fibers of E-glass has been investigated. Single-fiber fragmentation tests of E-glass/epoxy model composites have shown degradation of both the strength of the fiber and the strength of the interface after immersion in water at 25 and 75°C. This work has expanded to investigate the effects of water on the tensile and interlaminar properties of full-scale composite materials after immersion in water for comparison with the results from the single-fiber fragmentation test. One goal of this research is an assessment of the ability to predict composite structural properties from a small-scale test such as the single fiber fragmentation test; of particular interest is the possibility that the smaller scale of the test coupled with full immersion and elevated temperatures can provide an accelerated test for composite structures subjected to longer exposure under less severe environmental conditions. Four different composite test methods have been chosen to emphasize different aspects of the problem: tension tests of unidirectional layups should reflect the degradation of the fiber strength, while testing unidirectional layups in compression and in Mode I and Mode II delamination fracture should be more indicative of the degradation of the interface. Two different fiber coatings have been used in an effort to vary the nature of the glass/epoxy interface, and the specimens have been immersed at both 25 and 75°C to investigate the influence of temperature.