Multi-Objective Geometry Optimization of Additive-Manufactured Hexagonal Honeycomb Sandwich Beams Under Quasi-Static Three-Point Bending Loading.

This research paper presents the findings of a design optimization analysis conducted on additive-manufactured thermoplastic sandwich structures with hexagonal honeycombs subjected to quasi-static three-point bending. Based on experimental results, finite element analysis, and analytical models, the relationship between four selected design variables (i.e., cell wall length ratio, cell wall angle, cell wall thickness, and skin thickness) and the structure's mass, flexural stiffness, and maximum load capacity was determined. The influence of each design variable on the aforementioned structural properties was mathematically represented using three scaling laws to formulate a multi-objective optimization problem. Two conflicting objective functions, one for the mass and the other for the reciprocal of the maximum load capacity, along with a nonlinear constraint equation for the minimum allowed flexural stiffness of the sandwich structure were developed. The optimal values of the design variables were determined using two optimization methods, the Pareto optimal front and genetic algorithm, and by applying the Improved Minimum Distance Selection Method (IMDSM). Optimized designs were obtained for different values of flexural stiffness. It was found that, independently of the stiffness constraint value, the optimal value of the cell wall length ratio was 0.2 and the optimal cell wall thickness was 1.4 mm, which correspond to the minimum cell wall length ratio and maximum cell wall thickness considered in this study, respectively. On the other hand, if higher flexural stiffness is required for the structure, both cell wall angle and skin thickness must be increased accordingly. Furthermore, an increase in flexural stiffness is accompanied by an increase in both the mass and maximum load capacity of the structure.