On the Hygrothermal Response of Laminated Composite Systems †

The hygroscopic nature of polymeric systems, which find widespread application as matrices in advanced composite materials, requires that dila tations induced by the absorption of moisture be considered m the stress analysis of composite laminates. Considerable attention has recently been focused upon the reduction m both strength and constitutive properties of fiber-reinforced polymeric composites at elevated temperatures when the composite has been subjected to environments which enhance moisture diffusion. This apparent degradation in elevated temperature properties may be magnified even more by residual stresses induced by both the hygroscopic and thermoelastic characteristics of the unidirectional com posite. A unified treatment of the hygrothermal response of the laminated composite plate element is derived. The analysis develops effective mois ture inplane force resultants and bending resultants, which when coupled with mechanical and thermal loadings, yield laminae stresses resulting from the total hygrothermal and mechanical loading environment. Solutions of the classical diffusion equation are obtained yielding mois ture profiles through the laminate thickness. Typical composite laminates consisting of T300/5208 graphite-epoxy are analyzed. Results reveal both the magnitude and distribution of hygrothermally induced stresses.