Study of Environmental Effects on Thermomechanical Behavior of Resin-Base Composites

A combined analytical and experimental study was designed to characterize moisture obsorption in graphite/epoxy composite materials. Tests were designed to investigate the influence on moisture absorption of a number of composite parameters including thickness, fiber volume, and lay-up configuration. The environmental parameters investigated were the effects of temperature and humidity; the effect of small applied strains was also evaluated by use of four point bend specimens. The results were analyzed by comparing the weight gain characteristics of the various panels, and by evaluating the coefficients of diffusion for the specimens. Based on these diffusivities, one and three dimensional solutions to Fick's equation were evaluated. A micromechanical model for laminates were developed and analyzed; the experimental data showed the model to be a lower bound solution. Moreover, the results indicate the classical solution to the one dimensional Fick's law based on effective diffusivity can be used to predict weight gain of a graphite/epoxy panel due to the presence of water. This model cannot currently predict secondary diffusion effects. The results of the bending tests showed no effect of small applied strains on the weight gain of the bend specimens. (Author)