Heat and water mass transfer modeling in polyimide based advanced composites

In this work, analytical and numerical models were utilized to analyze the absorption of water in polyimide resins. Past studies showed that the prese nce of water or other fluids often had deleterious effects on the long term performance of composite materials. Therefore, the issue of concern addres sed here was the hydrophilic nature of polyimide resins and its impact on p olyimide utilization as matrix resins in fiber reinforced composites design ed 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 in vestigate the absorption of water in these materials. Initially, analytical models based on Fickian diffusion assumptions were developed, with deviati ons from this ideal behavior expressed by various changing boundary conditi ons. As analytical models could not provide a solution to complex non-Ficki an cases, finite differential methods were applied to develop numerical mod els that accounted for concentration dependent coefficients of diffusion, a s well as periodic boundary conditions relevant to hygrothermal cycling. Su ch models were found to provide excellent agreement with the experimental d ata. Additionally, thermal profiles for the simulation of an airplane engin e 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. (C) 2000 Elsevier Science Ltd. All rights reserved.