3D printed metamaterials leverage complex geometry to damp mechanical vibrations

In science and engineering, it is unusual for innovation to come all at once. It is most often a meticulous work through which the extraordinary gradually becomes ordinary.

But we may be at an inflection point on this path when it comes to engineered structures whose mechanical properties are unlike anything seen before in nature, also known as mechanical metamaterials. A team led by researchers from the University of Michigan and the Air Force Research Laboratory (AFRL) has shown how to 3D print complex tubes that can use their complex structure to counteract vibrations.

Such structures could be useful in various applications where users wish to damp vibrations, including transportation, civil engineering, etc. The team’s new study, published in the journal Applied physical examinationdraws on decades of theoretical and computational research to create structures that passively block vibrations trying to travel from one end to the other.

“That’s where the real novelty is. We’ve realized: We can actually make these things,” said James McInerney, a research associate at AFRL. McInerney was previously a postdoctoral researcher at UM and worked with Xiaoming Mao, a professor of physics who was also an author on the new study.

“We are optimistic that these methods can be applied for good purposes. In this case, it is vibration isolation,” McInerney said.

Serife Tol, associate professor of mechanical engineering at UM, contributed to the study, as did Othman Oudghiri-Idrissi of the University of Texas and Carson Willey and Abigail Juhl of AFRL.

“For centuries, humans have improved materials by changing their chemistry. Our work builds on the field of metamaterials, where it is geometry, rather than chemistry, that gives rise to unusual and useful properties,” Mao said. “These geometric principles can be applied from the nanoscale to the macroscale, which gives us extraordinary robustness.”

Structural foundations

The new study is a mix of old-fashioned structural engineering, relatively new physics and advanced manufacturing technologies, like 3D printing, that are becoming more and more impressive, McInerney said.

“There is a real probability that we will be able to make materials from scratch with crazy precision,” he said. “The vision is that we’re going to be able to create very specifically architected materials and the question we’re asking ourselves is: ‘What can we do with that?’ How can we create new materials that are different from those we usually use? »

However, as Mao said, the team does not change the chemistry or molecular composition of the materials. Researchers are studying how to use precise control of the shape of an arbitrary building material to achieve new beneficial properties.

Human bones and plankton “shells,” for example, benefit from this strategy in nature. They are constructed with complex geometries to achieve more than would be expected from the substances they are made from. Using tools like 3D printing, researchers can now apply this strategy to metals, polymers, and other materials to create desired properties that were not previously achievable.

“The idea is not to replace steel and plastic, but to use them more efficiently,” McInerney said.

New school meets old school

Although this work draws on modern innovations, it has important historical foundations. There is, for example, the work of the famous 19th century physicist James Clerk Maxwell. Although he is best known for his work in electromagnetism and thermodynamics, he also became interested in mechanics and developed useful design considerations for creating stable structures with repeating subunits called Maxwell networks, McInerney said.

Another key concept behind the new study emerged in the second half of the 20th century, when physicists discovered that interesting and puzzling behaviors appeared near the edges and boundaries of materials. This led to a new field of study, known as topology, which is still very active and strives to explain these behaviors and help exploit them in the real world.

“About ten years ago, a seminal publication discovered that Maxwell lattices could exhibit a topological phase,” McInerney said.

Over the past several years, McInerney and colleagues have explored the implications of this study as they relate to vibration isolation. The team built a model explaining this behavior and how to design a real object that would exhibit it. The team has now proven that their model is at its most advanced stage by making such objects with 3D printed nylon.

A quick look at the structures reveals why making them used to be such a challenge. They look like a chain link fence that has been folded and rolled into a tube with an inner and outer layer connected. Physicists call these tubes kagome, a reference to traditional Japanese basket weaving that used similar patterns.

This, however, is only the first step in realizing the potential of such structures, McInerney said. For example, the study also showed that the better a structure is at suppressing vibration, the less weight it can support. This is a costly, if not unacceptable, trade-off in terms of applications, but it highlights interesting opportunities and questions that remain at a fundamental level, he said.

As such new structures are created, scientists and engineers will need to develop new standards and approaches to test, characterize and evaluate them, a challenge that excites McInerney.

“Because we have new behaviors, we are still discovering not only the patterns, but also how we would test them, what conclusions we would draw from the tests, and how we would implement those conclusions in a design process,” he said. “I think these are the questions that need to be honestly answered before we start answering questions on applications.”