A model is proposed which relates externally applied tensile stresses to changes in absorption capacity as well as diffusion rate. The model postulates that changes seen in the diffusion process are the result of stress-dependent changes in the free volume of the epoxy resin. The free volume changes of the resin are calculated through laminate plate theory, which itself becomes a function of fiber angle as well as a host of elastic properties of the constituents. Consequently, according to the proposed model, changes in diffusion parameters are dependent upon the magnitude of applied stress, the loading angle, as well as elastic properties of the constituents.
Additionally, a finite element model is presented. The proposed finite element model establishes an analogy between thermal and mass diffusion for use in solving the moisture diffusion problems, both in free and stressed states. Input parameters for the FE model are found through use of the previously established mathematical diffusion model.
In order to experimentally verify the proposed models, a series of epoxy glass laminate samples were manufactured at varying fiber angles and immersed in a moist environment while subjected to varying levels of tensile loading. Weight gain measurements were recorded throughout the diffusion process until full saturation was achieved. The experimental values exhibited excellent agreement with both the suggested theoretical model and the finite element model.