3D-printed metamaterials harness complex geometry to dampen mechanical vibrations

In science and technology, innovation rarely comes in one fell swoop. Most often, this is painstaking work, thanks to which the unusual gradually becomes ordinary.

But we may be at a turning point in this journey when it comes to engineering structures, whose mechanical properties They are unlike anything previously seen in nature and are 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 suppress vibrations.

Such designs can be useful in a variety of applications where people want to dampen vibrations, including transportation, civil engineering and more. New team research published in the magazine Physical check appliedis based 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 realize that we can actually create these things,” said James McInerney, a research scientist at AFRL. McInerney was previously a postdoctoral fellow at UM and worked with Xiaoming Mao, a professor of physics who is also an author of the new study.

“We hope they can be used for good purposes. In this case, it’s vibration isolation,” McInerney said.

Serife Tol, assistant professor of mechanical engineering, contributed to the study, as did Deed Osman Udgiri-Idrissi of the University of Texas and Carson Willey and Abigail Juhl of Afrl.

“Over the centuries, people have improved materials by changing their chemical composition. Our work is based in the field of metamaterials, where it is geometry, not chemistry, that gives rise to unusual and useful properties,” Mao said. “These geometric principles can be applied at both the nanoscale and the macroscale, giving us exceptional reliability.”

Structural Basics

The new research is a combination of old-school structural design, relatively new physics and advanced manufacturing technologies such as 3D printing that are becoming increasingly impressive, McInerney said.

“There is a real possibility that we will be able to produce materials from scratch with crazy precision,” he said. “The idea is that we will be able to create materials with very specific architectures, and we ask the question: 'What can we do with this?' How can we create new materials that are different from what we are used to using?”

However, Mao said the team is not working on the chemistry or molecular composition of the materials. Researchers are exploring how they can use precise control of the shape of a free-form building material to identify new beneficial properties.

For example, human bones and planktonic shells use this strategy in nature. They have complex geometries to get more out of the substances they are made from than you might expect. Using tools like 3D printing, researchers can now apply this strategy to metals, polymers and other materials to achieve desirable properties that were previously unattainable.

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

New school meets old school

While this work does draw on modern innovations, it has an important historical basis. First, it is the work of the famous 19th century physicist James Clerk Maxwell. Although he is best known for his work in electromagnetism and thermodynamics, he was also interested in mechanics and developed useful design solutions for creating stable structures with repeating subunits called Maxwell lattices, McInerney said.

Another key concept in new research emerged in the second half of the 20th century, when physicists discovered that interesting and mysterious behavior occurred near the edges and boundaries of materials. This led to the emergence of a new field of research known as topology, which is still very active today and works to explain this behavior and help benefit from it in the real world.

“About ten years ago, there was a seminal publication that showed that Maxwell lattices can exhibit a topological phase,” McInerney said.

Over the past few years, McInerney and his colleagues have explored the implications of this research for vibration isolation. The team created a model to explain this behavior and how to design a real object that would exhibit it. Now the team has proven that its model is at its most advanced stage by actually creating such objects from 3D printed nylon.

A quick look at the structures shows why building them used to be such a difficult task. They resemble a chain-link fence, folded and rolled into a tube with the inner and outer layers connected. Physicists call these tubes kagome, a reference to traditional Japanese basket weaving, which used similar patterns.

However, this is only the first step in realizing the potential of such structures, McInerney said. For example, the study also found that the better a structure dampens vibrations, the less weight it can support. It's a costly and potentially unacceptable trade-off from an application perspective, he says, but it highlights interesting opportunities and questions that remain at a fundamental level.

As such new structures are created, scientists and engineers will have to develop new standards and approaches for testing, characterizing and evaluating them, a challenge that excites McInerney.

“Because we have this new behavior, we're still discovering not only the models, but how we test them, the conclusions we'll draw from the tests, and how we incorporate those conclusions into the design process,” he said. “I think these are questions that need to be answered honestly before we start answering questions about applications.”