Abstract
Residual stresses are introduced in composite laminates during curing as a result of differential thermal expansion of the various plies. Residual stresses coupled with asymmetries in the laminate produce warpage. To study these phenomena, symmetric and asymmetric glass-fabric-reinforced laminates were fabricated. The laminate material was fully characterized by determining its physical and mechanical properties at room and elevated temperatures. Thermal strains during curing and subsequent thermal cycling were measured by means of embedded strain gages. Residual stresses were then calculated using the mechanical properties determined before. Warpage for known types of asymmetry was calculated by means of lamination theory and compared with experimental measurements using a projection moire technique. The residual stresses in the studied laminates were very low, owing to the balancing effect of the woven-fabric reinforcement. A crossplied antisymmetric laminate showed saddle-shaped warpage in agreement with the analytical prediction. Unexpected warpage found in symmetric laminates may be due to imperfections in fiber orientations and/or temperature nonuniformities during laminations.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Chamis, C.C., “Lamination Residual Stresses in Cross-Plied Fiber Composites,” Proc. 26th Annual Conf. SPI, Reinforced Plast./Comp. Div., 17-D (1971).
Hahn, H.T., “Residual Stresses in Polymer Matrix Composite Laminates,”J. Comp. Mat.,10,266 (1976).
Daniel, I.M. and Liber, T., “Lamination Residual Stresses in Fiber Composites,” IITRI Rep. D6073-1, for NASA-Lewis Research Center, NASA CR-134826 (1975).
Daniel, I.M., Liber, T. and Chamis, C.C., “Measurement of Residual Strains in Boron/Epoxy and Glass/Epoxy Laminates,” Composite Reliability, ASTM STP 580, Amer. Soc. Test. and Mat., 340 (1975).
Daniel, I.M. andLiber, T., “Effect of Laminate Construction on Residual Stresses in Graphite/Polyimide Composites,”Experimental Mechanics,17,21 (1977).
Daniel, I.M. and Liber, T., “Lamination Residual Strains and Stresses in Hybrid Laminates,” Composite Materials: Testing and Design (4th Conf.), ASTM STP 617, Amer. Soc. Test. and Mat., 331 (1977).
Weitsman, Y., “Residual Thermal Stresses Due to Cool-Down of Epoxy-Resin Composites,”J. Appl. Mech.,46,563–567 (Sept. 1979).
Chamis, C.C., “A Theory for Predicting Composite Laminate Warpage Resulting from Fabrication,” Proc. 30th Tech. Conf., Reinforced Plast./Comp. Inst. Soc. of Plast. Ind., Sect. 18-C (1975).
Hyer, M.W., “Calculations of the Room-Temperature Shapes of Unsymmetric Laminates,”J. Comp. Mat.,15,296–309 (1981).
Hyer, M.W., “The Room-Temperature Shapes of Four-Layer Unsymmetric Cross-Ply Laminates,”J. Comp. Mat.,16,318–340 (1982).
Ishikawa, T. andChou, T.W., “Stiffness and Strength Behavior of Woven Fabric Composites,”J. Mat. Sci.,17,3211 (1982).
Ishikawa, T. andChou, T.W., “Elastic Behavior of Woven Hybrid Composites,”J. Comp. Mat. 16,2 (1982).
Jones, R.M., Mechanics of Composite Materials, Scripta Book Co., Washington, D.C., Chap. 4 (1975).
Tsai, S.W. andHahn, H.T., Introduction to Composite Materials, Technomic Publ. Co., Westport, CT (1980).
Harper, B.D. andWeitsman, Y., “Environmental Effects in Cross-Ply Composites,”Int. J. Sol. and Struct.,21 (8),907–926 (1985).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Zewi, I.G., Daniel, I.M. & Gotro, J.T. Residual stresses and warpage in woven-glass/epoxy laminates. Experimental Mechanics 27, 44–50 (1987). https://doi.org/10.1007/BF02318862
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF02318862