Heat and water mass transfer modeling in polyimide based advanced composites

Abstract

In this work, analytical and numerical models were utilized to analyze the absorption of water in polyimide resins. Past studies showed that the presence of water or other fluids often had deleterious effects on the long term performance of composite materials. Therefore, the issue of concern addressed here was the hydrophilic nature of polyimide resins and its impact on polyimide utilization as matrix resins in fiber reinforced composites designed for aircraft parts. To fully understand and characterize the behavior of the polyimide resins, it was necessary to evaluate the water concentration and thermal profiles that might be encountered during service conditions. Consequently, several models of heat and mass transfer were developed to investigate the absorption of water in these materials. Initially, analytical models based on Fickian diffusion assumptions were developed, with deviations from this ideal behavior expressed by various changing boundary conditions. As analytical models could not provide a solution to complex nonFickian cases, finite differential methods were applied to develop numerical models that accounted for concentration dependent coefficients of diffusion, as well as periodic boundary conditions relevant to hygrothermal cycling. Such models were found to provide excellent agreement with the experimental data. Additionally, thermal profiles for the simulation of an airplane engine core cowl were also calculated. Overall, this work provided the means to understand the hygrothermal conditions within a polyimide composite during laboratory simulated service conditions.