Anisotropic water diffusion in mechanical joints of fiber-reinforced composite panels: numerical study

This paper presents numerical study on the effect of diffusion anisotropy on the accumulation of moisture in the net-tension and shear-out failure planes in fiber composite bolted connection. A composite plate containing four bolt holes was investigated. The effect of the edge distance-to-hole diameter ratios and the distance between two holes-to-hole diameter ratio was analyzed. The diffusion process was described by Fick’s law, and it was assumed that moisture is penetrating only through bolt holes in the composite joints. Technical computing software Mathematica was used to solve the 2D diffusion equation over the plate region and find the moisture concentration distribution. The numerical approach was validated against analytical expressions for diffusion in 2D plate. It was found that diffusion anisotropy ratio strongly influences the equilibrium moisture content. It was shown that depending on the joint geometry, there are significant differences in moisture content on the expected failure paths because of sorption anisotropy, which can lead to premature failure due to the increased damage done to the composite matrix, interface, interphase, and fibers.