3D Printing of Topologically Optimized Auxetic Structures and Their In-Plance Performance Evaluation

Abstract

The auxetic structures, because of their negative Poisson ratio, have a lot of potential applications in the aerospace and automobile industry due to their exceptional mechanical properties under bending, shear, and compression loads. However, because of the rotational or bending deformation nature of their elements/ligaments, they normally possess low in-plane stiffness, due to which their applications become limited where high stiffness, energy absorption, and strength are simultaneously desired. So, there was a requirement of creating novel designs of auxetic structures capable of sustaining high in-plane loads. Moreover, an important design tool i.e. shape optimization was not deeply explored in the designing of the auxetic structures. Furthermore, any statistical study on the unit cell geometry parameters of auxetic structures was not yet carried out to sort out their best combination, at which the mechanical properties of auxetic structures become optimum. Therefore, to address these gaps, three novel auxetic structures were designed in this research, and their mechanical properties under compression and bending loads were investigated in comparison to the conventional re-entrant auxetic structure with the help of experimentally validated Finite Element Analysis (FEA) models. This comparison assisted in revealing if and how the new designs are superior. Then, the shape optimization was applied to all the structures under study to improve their specific strength and thus realize a new level of lightweight fabrication of auxetic structures. Later, the unit cell geometry parameters of the best-performing structure were optimized with the help of a statistical approach (i.e. Design of Experiment). Finally, the unit cell geometry optimized structures were also shape optimized to investigate the effect of simultaneous application of both techniques. The Young’s modulus and energy absorption capacity of the novel structures were found to be up to 122% and 200% higher than the conventional structure, respectively. Similarly, the mechanical performance of the shape-optimized structures was found to be considerably improved than the un-optimized structures i.e. up to 120% improvement in flexural modulus was noticed. Moreover, it was found that by unit cell geometry optimization of the auxetic structures their mechanical properties were enhanced up to 88%. Further, by combining the unit cell geometry optimization and shape optimization process the maximum amount of mechanical performance improvement xvi was observed i.e. up to 410%. Hence, in this research, novel topologically and geometrically optimized auxetic structures, with in-plane mechanical properties superior to the traditional ones were developed, which can be utilized to improve the performance of aerial, space, and road vehicles in terms of load-carrying capacity and fuel economy.