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Materials Science in Additive Manufacturing Gyroid non-pneumatic tires through additive manufacturing

parameters on air pressure. Air pressure can be affected by cracks, failure to demonstrate operational durability,
temperature and pressure fluctuation. More importantly, excessive noise and vibrations, and failure due to debris
loss of air pressure due to puncture can leave them getting stuck in the tire. Given these challenges, there is
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inoperable. Non-pneumatic tires (NPTs) or airless tires, a current need for innovative spoke designs in airless tires
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however, are free of these issues. The airless tires are built that offer enhanced mechanical stability.
from elastic structures, and function without relying on The design complexities in an NPT pose manufacturing
air pressure, effectively eliminating common issues like challenges. NPT variants with a solid elastic structure use
run-flat situations and frequent maintenance. Unlike a solid material filling between the inner hub and the
traditional tires, which are often discarded prematurely outer tread. The solid filler material is typically a hardened
due to punctures, airless tires are more eco-friendly rubber or plastic. While proving to be effective, solid NPTs
and offer substantial cost and energy savings. They also are overbuilt to provide durability but are inefficient at
enhance safety by minimizing the risk of accidents caused maximizing performance. This inefficiency arises from
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by tire failures. Due to these benefits, airless tires are used limitations in manufacturing lightweight NPT variants
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in a variety of vehicles, including bicycles, humvees, and with strut-based spoke design, requiring complex multi-
military all-terrain vehicles (ATVs), and are well-suited part assemblies that are expensive and cumbersome to build
for demanding extreme environments such as agricultural using traditional manufacturing methods. Moreover, when
operations, military and space exploration that involve compared to additive manufacturing (AM), traditional
uneven surfaces and extreme weather conditions, as well as manufacturing methods are not suitable for extreme
rugged landscapes such as mountains, deserts, and rocky environment applications where quick deployment and
terrains. 5-7
easy repair are important requirements. 21-23 AM offers great
Non-pneumatic tires (NPTs) present unique design promise for NPT manufacturing for extreme applications
challenges due to their inherently high stiffness and the because AM equipment could be deployed in extreme
cyclical nature of the loads they experience. These cyclic environments 24,25 to manufacture NPTs with minimal
loads limit material choices, as commonly used engineering human involvement.
materials cannot withstand high cycle fatigue. In addition, Triply periodic minimal surface (TPMS) lattices have
NPTs typically have a lower load-carrying capacity per a significant advantage over conventional strut-type spoke
unit weight compared to traditional pneumatic tires. The design when it comes to manufacturability, due to their
internal geometric structure of the supporting elements 26-28
plays a crucial role in determining both the stiffness and zero-mean curvature. TPMS surfaces can be additively
manufactured in any direction without requiring support
load-bearing capacity of NPTs. Despite advancements structures. In addition, the smooth curved surfaces
in NPT designs focused on modifying the geometric facilitate easy post-processing procedures. 29,30 TPMS
structure of the spokes, key challenges persist, such as topologies are defined using mathematically defined level-
buckling, deformation under high-impact loads, non- set functions and offer superior control over material
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linear responses to varying conditions, and damage caused response properties, such as surface area, relative density,
by debris lodging in the tire. To date, most research on 32-36
NPT design has extensively explored various designs for and volume fraction. The properties can be adjusted
spoke structures, including hexagonal honeycombs, 8-11 through geometrical functional gradation or by changing
radial columns 12-14 and re-entrant honeycomb patterns. 15,16 the constitutive material to achieve novel mechanical
However, radial beam spokes are prone to buckling behaviors. The smooth interconnectivity and self-
supporting characteristics of TPMS structures, compared
instability due to beam bending under load, making to other lattice designs, make them particularly suitable for
them vulnerable to damage from heavy impacts and large AM. 36-39
deformations. 8-10 While next-generation spokes, which
incorporate hexagonal or re-entrant honeycomb patterns, Various functionally graded designs have been
demonstrate improved deformation stability compared to studied to enhance the mechanical properties of uniform
radial beams, they remain susceptible to bending under TPMS structures, such as energy absorption, strength,
high impact and deformation conditions. In addition, and stiffness. Zhao et al. investigated the mechanical
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airless tires featuring honeycomb spokes tend to display properties and energy absorption of various functionally
non-linear responses when subjected to a wide range of graded sheet TPMS structures in comparison to uniform
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vertical loads. Recently explored designs include the sheet structures, concluding that the functionally graded
apollo lunar rover tires, the integral wheel tire (IWT), and designs demonstrated superior energy absorption capacity.
the Michelin Uptis (Unique Puncture-Proof Tire System). Ejeh et al. studied the impact of relative density gradation
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However, this approach resulted in the development of in TPMS gyroid structures on the flexural performance
Volume 3 Issue 4 (2023) 2 doi: 10.36922/msam.5022