Residual Stresses in Polymer Matrix Composite Laminates

Residual stresses in composites are induced during fabrication and by environmental exposure. The theory formulated can describe the shrinkage commonly observed after a thermal expansion test. Comparison between the analysis and experimental data for [02/± 45]s laminates of various material systems indicates that the residual stress-free temperature can be lower than the curing temperature, depending on the curing process. Ef-fects of residual stresses on ply failure including the acoustic emission characteristics are discussed. SCOPE Y DEFINITION A composite is composed of several different material phases and Bresidual stresses are induced due to the heterogeneity. Magnitude of these residual stresses depends on the history of environmental exposure as well as on the constituent properties. Typical residual stresses which are attracting increased atten-tion are the curing stress and the swelling stress. The former is induced by the thermal expansion mismatch during fabrication and the latter by the difference in swelling when moisture is absorbed. The curing stress in certain graphite/epoxy laminates may be large enough to cause ply failure in the absence of applied stress or premature failure upon tensile loading [1, 2J. In metal matrix composites such as boron/aluminum, the curing stress may cause plastic deformation in the matrix [3]. The damage observed in boron/aluminum composite after thermal fatigue can be attributed to the curing stress among others [4]. In the present paper we shall analyze the residual stresses resulting from fabrica-tion and moisture absorption and compare the analytical results with experimental data. Although the analysis method can be extended to metal matrix composites