: Mathematical models are suggested for calculating the reduced moisture diffusivities in unidirectional carbon fiber reinforced composites with hexagonal and tetragonal fiber alignment, parallel and perpendicular to the fiber direction, as a function of fiber volume fraction. The effective diffusion coefficients measured perpendicular to the fiber direction of 6 carbon fiber composites were determined as a function of temperature and relative humidity. The knowledge of the diffusion coefficients as a function of temperature, relative humidity, fiber volume fraction and composite geometry allow the prediction of the internal moisture distribution in a composite if the environment can be specified. A few simple examples have been illustrated.

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The Effect of Moisture on Carbon Fiber Reinforced Epoxy Composites. 1. Diffusion

Moisture diffusion analysis (MDA) has been developed as a new non-destructive evaluation methodology to monitor the strength degradation of graphite-epoxy composite materials. Studies of composite strength degradation due to high moisture identify reversible strength loss due to current moisture content and irreversible strength loss related to prior moisture exposure with microstructure damage. MDA measures current moisture content, directional diffusion coefficients, and moisture concentration profiles. MDA measurement utilizes an electrolytic cell to concurrently record cumulative .oisture content and moisture effusion rate. Extension of the diffusion analysis of Shen and Springer isolates directional diffusion coefficients and indicates a high sensitivity of MDA to moisture degradation of the fibermatrix interface. Extension of the methodology to analyze non-Fickian diffusion shows that MDA can be applied to locate regions of composite strength degradation related to hydrothenaal cycling effects. Studies which correlate MDA with ultrasonic response, and interlaminar shear strength of composite laminates subjected to localized moisture damage, show that MDA can be applied to map and locate low strength regions of a composite structure.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=4486&context=qnde

D. H. Kaelble

Papers

Moisture Diffusion Analysis of Composite Strength Degradation