0093-6413/87 $3.00 +.00 Copyright (c) 1987 Pergamon Journals Lid A CONSISTENT REFINED THEORY FOR FLEXURE OF A SYMMETRIC LAMINATE

Any two-dimensional plate theory is an approximation of the real three-dimen-sional elasticity problem. The classical laminated plate theory is based on the Kirchhoff hypothesis and ignores the effects of transverse shear deforma-tion, normal stress, normal strain and nonlinear in-plane normal strain dis-tribution through the plate thickness [ 1,2]. Two types of composite plates are generally identified in practice: (i) 'fibre reinforced laminates ' in which layers of composite materials with high ratios of Young's-to-shear modulii are bonded together and (2) 'sandwiches ' in which layers of isotropic materials with some layers having significantly lower elastic modulii than others, are bonded together. The effects of shear deformation are signific-ant in these situations and thus the classical theory is inadequate. Exact elasticity solutions for flexure of some standard composite and sandwich plate problems have been obtained by Pagano [ 3] and Pagano and Hatfield [4]. Whitney [5] and Mau [6] have presented first-order laminate theories in which transverse shear strain is assumed constant through the thickness. This re-quired, however, use of a transverse shear correction factor which generally varied with the lamination scheme. Theories based on realistic displacement models which give rise to nonlinear distributions of in-plane normal strains and transverse shear strains have been developed by Murthy [ 7], Reddy [ 8], Phan and Reddy [ 9] and more recentl