Moisture Diffusion In Composites Research Articles

The Two Stage Moisture Diffusion Model for Non-Fickian Behaviors of 3D Woven Composite Exposed Based on Time Fractional Diffusion Equation

The moisture diffusion behaviors of 3D woven composites exhibit non-Fickian properties when they are exposed to a hydrothermal environment. Although some experimental works have been undertaken to investigate this phenomenon, very few mathematical works on non-Fickian moisture diffusion predictions of 3D woven composites are available in the literature. To capture the non-Fickian behavior of moisture diffusion in 3D woven composites, this study first utilized a time fractional diffusion equation to derive the percentage of moisture content of a homogeneous material under hydrothermal conditions. A two-stage moisture diffusion model was subsequently developed based on the moisture diffusion mechanics of both neat resin and 3D woven composites, which describes the initial fast diffusion and the long-term slow diffusion stages. Notably, the model incorporated fractional order parameters to account for the nonlinear property of moisture diffusion in composites. Finally, the weight gain curves of neat resin and the 3D woven composite were calculated to verify the fractional diffusion model, and the predicted moisture uptake curves were all in good agreement with the experimental results. It is important to note that when the fractional order parameter α < 1, the initial moisture uptake will become larger with a later slow down process. This phenomenon can better describe non-Fickian behavior caused by initial voids or complicated structures.

Micromechanics of Moisture Diffusion in Composites with Impermeable Fibers

The objective of this paper is to determine the effect of fiber volume fraction on effective diffusivity of composites with impermeable fibers using finite elements. Both hexagonal and square fiber arrangements were studied. It is found that for low to moderate fiber fractions (Vf< 40%)the effective diffusivity was essentially the same for both fiber arrangements and the calculated values agreed very well with Hashin’s formula. For high fiber fractions (Vf> 40%)there were significant differences, but the behavior was still quite simple. A very simple closedform formula, which consists of Hashin’s formula for part of the range and a straight line for the rest, is proposed for calculating the effective diffusivity as a function of fiber volume fraction. The simple formula predictions matched the finite element predictions extremely well.

Modified One-Dimensional Fickean Solution for Moisture Absorption in Composites

In this paper an empirical modification in the one-dimensional Fickean solution of moisture absorption by composites has been suggested. Certain physical factors due to which actual process of moisture diffusion in composites differs from the classical diffusion descnbed by Fick's law have been discussed. It is shown that most of the factors which attnbute to the differences between the theoretical prediction and the observed be havior can be accounted for, just by incorporating some parameters in the Fickean solution itself.