Nuclear reaction analysis for measuring moisture profiles in graphite/epoxy composites

Abstract

The absorption of moisture by epoxy resins and graphite/epoxy composites causes degradation of mechanical properties at elevated temperatures. In order to study the rate of moisture absorption and transport in fiber-reinforced epoxy, nuclear reaction analysis methods have been used to measure the localized moisture content in these materials. The experimental conditions have been determined for which the D(³He, p)⁴He reaction meets the particular requirements for measuring moisture profiles in composites. A description of the experimental procedures and the method of defining deuterium reference standards for measuring absolute concentrations of D₂O is presented. The technique has been applied to fully and partially saturated epoxy resin and composite specimens that have been subjected to various conditions of exposure. The moisture distribution has been measured through the thickness of composite specimens with 12 μm resolution and with a level of detectability of 0.01 wt.% D₂O. The measured profiles in composites are compared to calculations of classical diffusion models of water transport.