Boundary layer state prediction of composite and sandwich plates via an enhanced higher-order shear deformation theory

An efficient and accurate method for the improved stress analysis using a conventional higher order shear deformation theory (HSDT) is presented. The main objective herein is to systematically establish the relationship between two independent displacement and stress fields through the mixed variational theorem (MVT). In the mixed formulation, the independent transverse shear stress field is taken from the fifth order polynomial-based zig-zag model, whereas the in-plane displacement field is assumed to be those of the conventional HSDT to amplify the benefits of numerical efficiency. Moreover, in-plane correction factor including the transverse normal stress effect is additionally considered to more accurately analyze the physical behavior for the general configuration of the laminated composite and sandwich plates. The resulting strain energy is referred to as an enhanced higher order shear deformation theory via the mixed variational theorem (EHSDTM). The EHSDTM has the same computational advantage as the conventional HSDT does, while allowing for improved local through-the-thickness variations of the displacements and stresses via the recovery procedure. Furthermore, the present theory can give a reliable solution for the shortcomings of earlier other theories, such as difficulties of predicting the edge effect in clamped boundary conditions. The accuracy and efficiency of the present theory are demonstrated by comparing results obtained herein to those of the 3-D exact solutions, 3-D FEM and other theories reported in literature.