CHAIN MAIL ON STEROIDS
A research team from CalTech has created a new chain mail-inspired material with unique properties.
Written by Kayt Sukel
A material made from linked octahedrons. Photo: CalTech
Testing the impact resistance of the material when unjammed (soft). Photo: CalTech
Testing the impact resistance of the material when jammed (rigid). Photo: CalTech
JUST BEFORE THE PANDEMIC, Chiara Daraio found herself captivated by a museum exhibit featuring medieval chain mail. As a student, her work focused on understanding how granular systems, like sand or coffee grounds, can become almost like architected materials when put in an “ordered form.”
“Granular materials are special—they have very complex physical behavior,” explained Daraio, the G. Bradford Jones Professor of Mechanical Engineering and Applied Physics at the California Institute of Technology (CalTech). “There are decades of academic studies and physics-based analyses looking at the mechanics of granular systems as being somewhere between flowing, like when you pour sand in a glass, and then kind of solid when coffee grains are vacuum packed.”
As she looked at the intricate medieval armor, she thought the links in the chain mail were quite like coffee grains. And they, too, should move and interact with one another in interesting ways.
“The links in chain mail have a complex topological shape—but if you take each right on its own, it can move freely,” she said. “We started to think about making chain mails that are 3-D printed and what we could do with them.”
After creating woven sheets of chain mail that become stiff and solid under pressure, Daraio and colleagues set their sights on creating a more complex three-dimensional shape. The resulting material is called a polycatenated architected material (PAM)—a material that was born from Daraio’s fascination in understanding the boundary between discrete and continuum media and how to “exploit it to make materials with interesting properties.”
PAMs in action. Video: Wenjie Zhou and Peter Holderness/Caltech
PAMs are 3-D objects made up of a variety of different shapes linked together like the chains you see in chain mail. The group modeled each different PAM shape by modeling lattice structures naturally found in crystalline substances, but instead of having a fixed particle in the lattice, those particles were replaced by intricate ring formations or “cages with multiple sides.” The resulting two-inch cube materials were printed using a 3-D printer using materials ranging from acrylic polymers to different metals.
“Depending on the complex shape you choose, the interlocking of the rings becomes more complex. There are so many different ways the different elements can link and move about with respect to one another,” Daraio said.
To understand PAMs’ utility as a material, the group had to understand how those different elements would affect the behavior of the whole object. They decided to analyze the physical and mechanical properties to get there. Daraio said it was difficult, at first, to think about the best types of tests to undertake.
“When you hold [PAMs] in your hand, it feels like rice. You can jiggle it a bit and it has the same tactile feeling you get when you hold a bunch of grains of rice,” she said. “It moves a bit like a liquid. But, of course, it is not a liquid.”
“The links in chain mail have a complex topological shape—but if you take each right on its own, it can move freely. We started to think about making chain mails that are 3-D printed and what we could do with them.”
—Chiara Daraio, G. Bradford Jones Professor of Mechanical Engineering and Applied Physics at the California Institute of Technology
The group ultimately decided to use standard mechanical and physical analyses to stress test the new materials, including compression, shear, lateral force, and rheology tests. In doing so, they discovered the architected material had some unique physical properties when pressed, twisted, or sheared. For example, shear stress allowed the PAMs to “flow” like a liquid, with very little resistance. Compression resulted in PAMs stiffening up like a solid.
“There was really a wealth of surprising behaviors to analyze,” she said. “It’s really like a new type of matter.”
When asked what happens next, Daraio said the team will continue to analyze the dynamic response of the system. Understanding more about the physical and mechanical properties of PAMs will help determine what type of applications they would be best suited for. Since PAMs can flow like sand, perhaps they are equally as good at absorbing energy as sandbags, an age-old go-to used to minimize the impact of different forces.
When stiffened, the material has the potential to act as a sturdy bridge. Photo: CalTech
“We want to know, what are PAMs’ energy absorption characteristics?” she said. “For example, what are the wave propagation properties through these structures on impact? As we brainstorm possible applications, it is possible, if the energy absorption is there, we could make a helmet core that is lightweight but more effective at dispersing energy during impact. This could also be extended to other types of wearable protections once we can quantify how PAMs are affected by multiple types of loading.”
But PAMs may also work well in soft robotic or biomedical device applications, as microlattices made of PAMs could provide “scaffolds or building blocks” for small and flexible machines, she added.
“There is a rich opportunity space for many different functionalities,” Daraio said. “These materials have such unique properties. We are only starting to consider how they could be used.”
Kayt Sukel is a technology writer and author in Houston.
ADVERTISEMENT
© 2025 The American Society of Mechanical Engineers. All rights reserved.