Abstract
A model for the effect of external uniaxial loading on the equilibrium moisture content in uni-directional composite materials is proposed. The model attributes the effect to a change in the free volume of the resin matrix, which is equal to its volume strain.M ∞ of the stressed state is calculated as a function of the stress level, the volume fraction of the fibres and the angle between the applied stress and the fibre direction. Moisture absorption experiments were performed on pure epoxy matrix and on graphite-epoxy composites. The effect of the parameters mentioned above onM ∞ was examined, and excellent agreement was found between the experimental and the calculated values. For stresses which were applied in the direction of the fibres (θ = O°) the experiment showed thatM ∞ decreased with the increase in the stress. We attribute this anomaly to the generation of residual stresses in the composite due to swelling.
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