Thermomechanical Performance of Sandwich Structures with Optimized Variable Thickness Lattice Cores

Shell-based structures are used by many components in aerospace design, as they offer efficient load-bearing capabilities and exceptional adaptability. This adaptability is realized through the strategic integration of stiffeners, localized tuning of section properties with fiber-reinforced materials, and the incorporation of variations in shell thickness. This study is dedicated to optimizing thickness distributions for shell-based sandwich structures through a deterministic iterative approach. Distinguishing itself from conventional optimization methods, this methodology does not rely on gradient calculations or random variables. Instead, finite element model results are harmonized with theoretical limits governing the distribution of strain energy in structures or materials residing on that theoretical threshold. Local, quantifiable deviations from this limit serve as the foundation for updating element thickness, propelling structural or material stiffness toward the theoretical boundary. To facilitate the iterative thickness optimization process, unit cell models of sandwich panels with advanced core materials are constructed. Conventional honeycomb core is considered as well as multiple truss cores (simple cubic, body centered cubic, octahedron, and octet) as well as a P-type triply periodic minimum surface. Unit cell models with periodic boundary conditions for the various sandwich structures enables high-fidelity simulations and an efficient means of determining optimal material allocation with minimal computational expense. Additionally, the approach accommodates fundamental loading states, such as pure membrane loading or pure bending, allowing for the extraction of effective section properties, including axial and flexural moduli. Extending the applicability of this methodology, thermal conductivity through the thickness and in the plane of the sandwich panels is computed for the sandwich panels comprised of variable thickness core materials and variable thickness skins. The thermomechanical panel properties are compared to the uniform thickness cases and amongst different choices of advanced core materials to provide insight to the tradeoffs that exist between thermal conductivity and mechanical performance of sandwich structures.