Partial-mixed formulation and refined models for the analysis of composite laminates within a FSDT

The present paper proposes a partial-mixed variational formulation for the analysis of composite laminates within the First-order Shear Deformation Theory (FSDT). The considered functional is recovered from the Hellinger-Reissner mixed principle and it appears to be particularly suitable for the determination of the FSDT governing equations since the transverse shear stresses are treated as independent variables. Accordingly, it is possible to obtain an accurate description of the shear stress profiles. Herein, the attention is concentrated on two different refined FSDT models, both having piecewise parabolic shear stress profiles. Furthermore, within one of the two refined models, the partial-mixed formulation is used to derive a performing finite element. Finally, analytical solutions from the classical and the refined FSDT models are compared to three-dimensional (3D) analytical solutions as well as to results obtained form the proposed laminate finite element.