Rapid prototyping assisted optimization and experimental three point bending evaluation of spreader bar structure

This paper investigates the advantages of optimization and rapid prototyping technology to aid in the improvement process of a spreader bar for an amphibious commuter aircraft, intended to withstand critical loads by combining topology and size optimization. The initial spreader bar, although lightweight, fails when subjected to a critical load. The geometrical parameters of the spreader bar's cross-section serve as the design variables for optimization. Topology optimization was performed first to minimize compliance under the fraction mass constraint, using a solid elliptical structure as a starting point. Following that, size optimization was conducted to reduce mass with the maximum stress constraint applied. The two-step topology and size optimization process resulted in a hollow ellipse cross-section with a spar in the middle as the optimized design. This optimized design turned the margin of safety from −0.37 to 0, which met the safety requirements. The initial and optimized designs were then scaled down and 3D printed using Polylactic Acid (PLA) material at a ratio of 1:5. Next, a three-point bending evaluation was carried out to compare the mechanical strength of the two designs. The experimental investigation revealed that the optimized design was considerably superior and more efficient than the initial design. The new parameter proposed in this research, maximum load efficiency, the optimized design was 7.16 N/g while the baseline design was about 1.94 N/g. The specific energy absorption of the spreader bar was improved from 6.32 J/g to 119 J/g. The findings of this study indicate that the combination of rapid prototyping and sequential topology–size optimization can be applied to real-world cases, taking into account design constraints from multiple aspects.