PSI - Issue 42

Manuel Sardinha et al. / Procedia Structural Integrity 42 (2022) 1098–1105 Manuel Sardinha / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Pneumatic tires (PTs) were firstly patented by Robert William Thomson in 1845 and represent the great majority of the tire types found on wheels of vehicles today. The inherent structural properties of the traditional PTs are the result of a complex production process that determines that it is easily punctured and that it needs frequent air pressure maintenance. Non-pneumatic tires (NPTs) emerge due to their potential performance advantages, and as an alternative that anticipates the shortcomings of the traditional PT. The NPT developed by Michelin® was of great importance in the research and development history of NPTs. Together with Michelin’s Tweel and X -Tweel models, international established companies like Bridgestone® and Goodyear® have publicly revealed their intention to commercialize NPTs. In 2013, Bridgestone revealed an NPT, claiming improved load-bearing capabilities and driving performance, and stating its development significantly considers environmental design aspects (eco-design). Some NPTs, or tireless wheels concepts, are already present in a substantial number of commercial solutions for golf carts, trailers, and lawnmowers, with most of these being made from rubber or polymers. Even so, researchers and engineers are still debating issues such as how to address trapped debris within the spokes, what is the best way to evenly distribute weight and consistently transmit loads, or how to predict the collapse and failure mechanisms of tires. Considering this, researchers’ endeavors are often related to a search for optimal functional designs, most often very complex and feasibly demanding. The geometrical design freedom offered by Additive Manufacturing (AM) technologies highlights its adequacy for the manufacturing of such complex geometries, that compose most NPTs. Even so, tires and wheel integrity and their mechanical behavior are a fundamental part of vehicle security, which together with the current lack of AM standards has delayed a faster, widespread adoption of NPTs. This research is focused on reviewing the mechanical design of non-pneumatic tires, and the adequacy of such designs to be additively manufactured by fused filament fabrication. 2. Non-pneumatic tires A typical NPT has an annular type of conception as seen in Fig. 1(a), and its common structure can consist of a hub, a middle design space usually composed of spokes or cellular structures, and an outer layer here identified as a shear ring, where the tread and shear core are located, Fig. 1(b).

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Fig. 1. Common Non-Pneumatic Tires composition. (a) Exploded view exemplifying annular conception; (b) Schematic front view of the components. Functional design by geometric manipulation of the spokes and shear ring design spaces has been one of the main focuses of NPTs research and development.