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One commonly cited shortcoming of 3D printing is its tendency to produce parts that aren’t quite as strong as those produced by more traditional kinds of manufacturing. That’s becoming less and less true, however, as materials and methods evolve, and 3D printed parts are demonstrating strength and robustness equal to or even surpassing that of their conventionally made counterparts. Now a pair of researchers at the University of Wisconsin-Madison have developed a 3D printed material that is much stronger than other materials used for building.

Engineering physics professor Roderic Lakes and graduate student Zachariah Rueger have 3D printed a material that behaves in a manner consistent with the Cosserat theory of elasticity, also known as micropolar elasticity. The theory factors in the underlying substructure of a substance when analyzing its performance in a high-stress environment. Lakes and Rueger used the theory to design a polymer lattice that is about 30 times stiffer when bent than would be predicted by classical elasticity theory. The lattice consists of polymer strips arranged in a repeating crisscross design, which can increase strength and durability.

Roderic Lakes

“When you have a material with substructure in it, such as some foams, lattices and fiber-reinforced materials, there’s more freedom in it than classical elasticity theory can handle,” Lakes said. “So we’re studying the freedom of materials to behave in ways not anticipated by the standard theory.”

That material freedom opens the door to creating new materials that are immune to stress concentration, i.e. tougher than any others. Practical applications could include making airplane wings more crack-resistant. If a crack forms in an airplane wing, stress concentrates around the crack, making the wing weaker.

“You need a certain amount of stress to break something, but if there’s a crack in it, you can break it with less stress,” said Lakes.

The Cosserat theory, however, generates materials in which stress is distributed differently, making them tougher. This behavior can be seen in bone, as well as certain types of foams. When making a foam seat cushion, though, engineers don’t have much control over the foam’s substructure, so they have limited ability to tailor the Cosserat effects.

[Image: Roderic Lakes]

Lakes and Rueger, however, can tune the Cosserat effects in their 3D printed material, making it extremely strong.

“We developed a material in which we have exceptionally detailed control over the fine structure of our lattice, and that enabled us to achieve very strong effects when bending and twisting the material,” said Lakes.

Most structures, including buildings, airplanes, bridges and electronic devices are designed according to classical elasticity theory – but this new form of designing, based on Cosserat theory, could yield materials that are vastly superior. 3D printing the material gives engineers more control over its properties and structure, which could potentially lead to a new way of building, or at least of designing certain components, such as the aforementioned airplane wings.

Rueger and Lakes published their work in a paper entitled “Strong Cosserat Elasticity in a Transversely Isotropic Polymer Lattice,” which you can access here.

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below. 

[Source: University of Wisconsin-Madison]

 

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