The effect of stress on the diffusion of water in glassy polymers is analytically treated. Utilizing the free volume concept the effect of stress on the free volume fraction is established and in turn is related to the diffusion coefficient yielding the following formula: Dσ = Doe(6 to 10)σ/G where Dσ and Do are the diffusion coefficients in the presence and absence of stress respectively, G is the shear modulus, and σ is the stress. Experiments are described which demonstrate that in a bent epoxy bar, more water is picked up at the tension side than at the compression side. Theory and experiment are discussed and compared.

The thermal expansion behavior of the two duplex systems, lead-fused silica and aluminum-silicon, has been investigated experimentally above and below room temperature. The microstructure in the first case consisted of fused silica particles in a lead matrix, while silicon constituted the dispersed phase in the second. The expansion coefficients always fell below those predicted by the simple rule of mixtures. A model is proposed and a new formula for the calculation of the thermal expansion coefficient of duplex materials is derived. The new formula fits experimental results better than Turner's formula. The role of microplastic yielding in high-inclusion-content composites is discussed.

The thermal expansion behavior of unidirectional, balanced angle-ply, and complex laminated graphite-epoxy composites, is studied. The expansion coefficient of the unidirectional composites is determined as a function of fiber orientation and is found to follow the simple equation αθ=αL cos2θ+αT sin2θ. Results obtained on angle-ply composites are in agreement with the predictions based on Halpin and Pagano's analysis. The applicability of the same approach to a panel of more complex construction is discussed. Hysteresis effects, observed in this panel, may be caused by interlayer stress relaxation.

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