Variable-density topology optimization and bending test of quasi-honeycomb sandwich structures

The topology optimization is considered to enhance the strength, stiffness, and specific energy absorption of a quasi-honeycomb sandwich structure since it can achieve the optimal distribution of materials. However, the existing material interpolation models do not make the topology structure have good clarity and stability. In the present study, a novel variable-density topology optimization based on an improved interpolation model is developed for the design of a quasi-honeycomb core. The combined cells are circularly spreading outward from the geometric center of the design domain, and the wall thickness function of the equivalent cell (i.e. a simplified model of the combined cell) is established on the basis of relative density. The SR material interpolation model is modified by adding the minimum elastic modulus term, fitting the weighting and penalty factors, and adopting the volume constraint of Bi-directional Evolutionary Structural Optimization (BESO). The optimization is conducted to minimize the compliance of the quasi-honeycomb core, in which the relative densities of equivalent cells are chosen as the design variables due to the mapping between topology elements and equivalent cells. The three-dimensional (3D) geometric models of original and optimized quasi-honeycomb cores, upper face sheets, and lower face sheets are built using SolidWorks and printed on a 3D printer. The deflection, strain, bending stiffness, and energy absorption under different material retention rates, restraint positions, and face sheet thicknesses are investigated by three-point bending tests. It is found that the improved SR material interpolation model is efficient for suppressing the grid dependence and checkerboard, and the mechanical properties of optimized quasi-honeycomb sandwich structures are significantly enhanced in comparison with original structures, confirming that the developed method provides important guidance for designing and optimizing the quasi-honeycomb sandwich structure.