Layout design of lattice-stiffener hybrid core for composite sandwich panel and experimental verification

Hybrid core composite sandwich panels, as representative load-bearing structures, have attracted significant attention in engineering due to their excellent mechanical properties. However, two key issues limit their optimal design: the misalignment of stiffeners and lattice materials along the thickness direction, and the excessive in-plane clustering of stiffeners. To overcome these challenges, this work presents a multi-material topology optimization approach integrating a penetration constraint and a maximum size constraint. The lattice core is modeled as a virtual material via an energy-based homogenization method. A local cylindrical search region is introduced to replace the conventional spherical search, thereby improving the alignment of stiffeners and lattices through the normal direction. The dimensions of in-plane stiffeners are controlled by constraining local porosity within a cylindrical search region, while the constraints are aggregated into a global form using the p-mean function. The optimization problem is efficiently solved using a gradient-based algorithm. Two numerical examples are provided to illustrate the design process and validate the effectiveness of the proposed method. Numerical and experimental results confirm that the proposed hybrid core composite sandwich panel exhibits superior mechanical performance.