Analytical and comparative assessment of shear deformation theories for sandwich beams with additively manufactured lattice cores

Additively manufactured (AM) lattice-core sandwich beams offer exceptional stiffness-to-weight ratios and design flexibility; however, their structural analysis is challenged by the pronounced heterogeneity and stiffness mismatch between stiff composite facesheets and compliant lattice cores. Classical Equivalent Single Layer (ESL) theories often fail to accurately represent the complex through-thickness deformation characteristics of such structures. This study presents a comprehensive comparative assessment of the Refined Zigzag Theory (RZT), the First-order Shear Deformation Theory (FSDT), and the Third-order Shear Deformation Theory (TSDT) against three-dimensional finite element (FEM) models for AM lattice-core sandwich beams subjected to sinusoidal distributed loading. Parametric investigations are conducted to evaluate the influence of facesheet lamination, core-to-facesheet thickness ratio, beam slenderness ratio, unit-cell strut aspect ratio, and lattice topology on the global and through-thickness structural response. The results demonstrate that RZT outperforms FSDT and TSDT in terms of overall prediction accuracy, particularly in configurations characterized by low core-to-facesheet thickness ratios, short beam spans, compliant lattice cores, and composite facesheets. These findings indicate that RZT provides an efficient and reliable reduced-order modeling framework for modern AM sandwich structures, offering high predictive accuracy at a fraction of the computational cost required by detailed numerical simulations.