Utilizing 3D printing technology in developing elastic auxetic materials for protective gear

Zihui Zhao

doi:10.7273/000004030

Most materials possess positive Poisson's ratios, meaning they become narrower/thinner in the transverse direction and longer in the loading direction when stretched. On the contrary, some special materials, known as auxetic materials, exhibit negative Poisson's ratios (NPR) and behave contrarily to what is expected. They expand laterally when stretched or shrink laterally when compressed. To date, a variety of auxetic geometry structures and models have been developed at different size levels from molecular to macroscopic. Example structures are re-entrant honeycomb structure, double-arrowhead, star-shaped structure, rotation squares, rotation triangles, and chiral structure. Auxetic materials have a number of enhanced properties because of the NPR effect, including increased shear modulus, indentation resistance, fracture toughness, and energy absorption. Motivated by the novel properties of auxetic material and the gap existing in producing efficient protective guard, this study aimed to developed 3D printed elastic auxetic structures using stereolithography 3D printer for protective gears and then evaluated the influence of different design and printing parameters on the mechanical properties of the structure. In the thesis, elastic resins were selected, and a 3D elastic double-u curve structure was designed based on previous research. The designed structure was produced by stereolithography 3D printing technology with several different printing and design parameters. Tensile and compression tests were then conducted to evaluate samples' mechanical properties including shape deformation, Poisson's ratio, modulus, and energy absorption capacity. The results showed that all samples exhibited expected NPR effect which Poisson's ratios ranged between -0.2 to -1.1. Material's mixture ratio, curing time, and structure's layer (unit cell) number directly affected samples' mechanical properties and NPR effects. Also, it was observed that the compressive behavior of double-u curve structure could be adjusted through modifying printing parameters. The more number of layers, the harder the material, the better the NPR effect, modulus, compressive stress, and energy absorption capacity. Among all cases, the "6-layer, 15s, 3:7" sample exhibited the greatest value of young's modulus, compressive stress, and energy absorption capacity. Additionally, by comparing to the results of auxetic foams in a previous study, it was found that the present structure had better energy absorption capability and NPR effect than auxetic and conventional foam. The present structure exhibited great potential in applications such as protective gears.

Utilizing 3D printing technology in developing elastic auxetic materials for protective gear

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