Modeling of Moisture Diffusion in Permeable Fiber-Reinforced Polymer Composites Using Heterogeneous Hybrid Moisture Element Method

摘要

This study proposes a two-dimensional heterogeneous hybrid moisture element method (HHMEM) for modeling transient moisture diffusion in permeable fiber-reinforced polymer composites. The HHMEM scheme is based on a heterogeneous hybrid moisture element (HHME), with properties determined through an equivalent hybrid moisture capacitance/conductance matrix. This matrix was calculated using the conventional finite element formulation in space discretization as well as the θ-method in time discretization with similar mass/stiffness properties and matrix condensing operations. A coupled HHME-FE scheme was developed and implemented in computer code MATLAB in order to analyze the transient moisture diffusion characteristics of composite materials containing multiple permeable fibers. The analysis commenced by comparing the performance of the proposed scheme with that of conventional FEM to model the moisture diffusion process. Both hexagonal and square fiber arrangements were studied. Having validated its performance, the scheme was then employed to investigate the relationship between the volume fraction of the permeable fibers in the resin composite and the rate of moisture diffusion. It was found that the moisture diffusion was significantly retarded as the volume fraction of the fibers increased. The HHMEM approach proposed in this study provides a straightforward and efficient means of modeling transient moisture diffusion in composite materials containing multiple permeable fibers. This is because only one HHME moisture char- acteristic matrix of fibers requires calculation for all HHMEs sharing the same characteristics. Furthermore, varying volume fractions can be modeled without modifying the original model simply by controlling the size of the inter-phase region within the HHME domain.