Accurate 3D stress recovery in variable stiffness composite plates: A higher-order isogeometric approach

Variable stiffness composites with curvilinear fibers present considerable computational challenges due to their spatially varying stiffness properties, strong anisotropic effects, and complex three-dimensional stress gradients. Therefore, appropriate theories are required to accurately represent the localized, non-linear transverse shear distributions caused by this heterogeneity, especially in thick laminates where shear deformation effects are significant. To address this, the present study introduces a three-dimensional stress recovery approach for variable stiffness composite plates that employs a Third-Order Shear Deformation Theory (TSDT) in conjunction with Isogeometric Analysis (IGA). By exploiting the high-order continuity of Non-Uniform Rational B-Splines (NURBS) basis functions, the proposed method enforces strong-form equilibrium to accurately recover interlaminar normal and shear stresses. Comprehensive comparisons with 3D finite element solutions across various variable stiffness laminate configurations demonstrate excellent agreement, underscoring the robustness of the proposed approach in predicting in-plane and transverse stress components. The results reveal that the TSDT-based isogeometric method delivers superior accuracy and convergence rates, particularly for thick plates with non-uniform stiffness distributions. Thus, this framework provides a powerful and computationally efficient tool for the design and analysis of advanced variable stiffness composite structures.