Swelling and hygroelasticiiy of polymeric composites

Investigated are the swelling and hygroelasticity of a unidirectional glass fiber‐reinforced epoxy composite subjected to boiling water for 24 hrs. By analogy with thermoelasticity, a coefficient of hygroelasticity is defined and shown to be predictable from the coefficients of the constituent materials by Schapery's equations. A mechanism for water penetration into the composite which combines capillarity and diffusion is proposed on the basis of the results of the water take‐up as a function of the composite specimen width (fiber length).