Abstract
The diffusion of water into unidirectional Kevlar fibre reinforced epoxy resins was studied as a function of fibre orientation and, for unidirectional (0°) composites, as a function of volume fraction (Vf). As the angle increased from 0 to 90°, the diffusivity increased dramatically; i.e. as more and more fibre-ends were exposed to the shorter diffusion path, the diffusivity increased. The equilibrium weight gain of water (M∞) in the composites increased with theV f of the fibre. M∞ of Kevlar fibre was calculated to be 4.9%. At a constantV f, specimens of the same thickness and width but different lengths were used to determineD 22, the diffusion coefficient of the composite along the fibre, andD 22, the diffusion coefficient transverse to the fibre. The initial data for the percentage weight gain against the square root of time were non-linear, which was attributed to the anisotropy of the diffusion process. The anisotropy arises from the much higher value ofD 11 as compared toD 22. AsV f increased from 0.37 to 0.59,D 11 increased from about 0.83 to about 4.2 × 10−12m2 sec−1, whereasD 22 decreased from 0.21 to 0.033 × 10−12 m2 sec−1. Thus, the ratioD 11/D 22 increased from 3 to over 100 as U increased. The experimental sorption data could be fitted satisfactorily with these diffusion coefficients.
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Aronhime, M.T., Neumann, S. & Marom, G. The anisotropic diffusion of water in Kevlar-epoxy composites. J Mater Sci 22, 2435–2446 (1987). https://doi.org/10.1007/BF01082128
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DOI: https://doi.org/10.1007/BF01082128