Transient Moisture Distribution and Hygrothermal Stress Analysis of Composite Laminates Using Equivalent Diffusion Methods

Abstract

It often takes several decades to reach moisture equilibrium state in composite laminates. Therefore, hourly varying fluctuating boundary moisture and temperature conditions require several millions of time steps to reach a state of equilibrium. A new transient analysis method is proposed to efficiently solve moisture distribution of composite laminates with rapidly fluctuating moisture and temperature boundary conditions. First, effective constant diffusivity and maximum moisture content were obtained by averaging transient temperature-dependent moisture diffusivity. In this way, a simple analytic solution can be effectively used to determine the transient moisture distribution under hourly fluctuating boundary conditions. Its efficiencies are demonstrated in three different conditions by comparing this method with a conventional finite difference method. Hygrothermal stress and material degradation were consequently discussed to demonstrate that we must avoid a simple knock-down factor or 40% devastating penalty and use more rational simulation and supporting data.