Ann Arbor Times

Engineers at the University of Michigan have developed a new approach to creating stiff and resilient materials for robotics and other applications, drawing inspiration from ancient basketweaving techniques. The research, published in Physical Review Research, shows that woven structures made from Mylar polyester ribbons can withstand repeated cycles of strong compression and return to their original shape, unlike continuous sheets of the same material which deform permanently.

Lead author Guowei (Wayne) Tu, a doctoral student in civil and environmental engineering at the university, became interested in the mechanical properties of woven baskets after reading about artifacts dating back to 7500 BCE. The research team explored whether there were mechanical benefits to weaving beyond its geometric and aesthetic qualities.

“We knew weaving is an effective way of creating 3D shapes from ribbons like reed and bark, but we suspected there must also be underlying mechanical advantages,” said Evgueni Filipov, associate professor of civil and environmental engineering and mechanical engineering at the University of Michigan and corresponding author of the study.

The team’s findings reveal that woven structures offer both high stiffness for supporting loads and resilience for enduring repeated use. “I’m very excited about harnessing the benefits of ancient basket weaving for modern 21st century engineering applications,” Filipov said. “For instance, lightweight woven materials for robotics would also help humans stay safer in case of human-robot collisions.”

To evaluate these properties, researchers created 3D metamaterials by weaving Mylar ribbons perpendicularly into different corner arrangements involving three to six planes. They compared these with similarly shaped structures made from continuous Mylar sheets by subjecting both types to progressive compression tests.

During testing, rectangular boxes made from woven materials returned to their original shape after being compressed by one centimeter. When further compressed—up to 14 centimeters or less than 20% of their original height—the woven boxes remained undamaged while the continuous-sheet versions suffered permanent deformation. High-resolution scans showed that stress in continuous structures was concentrated at certain points leading to buckling, whereas in woven structures stress was spread more evenly across the material.

Further experiments measured stiffness by determining how much force was needed to compress or bend the structures. Across all configurations tested, woven materials were found to be about 70% as stiff as their continuous counterparts. This result challenges common assumptions that woven systems are always flexible.

In demonstrations using more complex shapes, an L-shaped structure resembling a robot arm supported weight vertically while remaining flexible enough for movement. A four-legged robot prototype built with woven modules held up to 25 times its own weight and maintained function after overloading.

“With these few fundamental corner-shaped modules, we can design and easily fabricate woven surfaces and structural systems that have complex spatial geometries and are both stiff and resilient,” Tu said. “There is just so much more potential for how we could use these corner-based woven structures for future engineering design.”

The researchers also developed a concept for a wearable exoskeleton that uses varying stiffness throughout its structure for shock absorption while allowing mobility. Looking ahead, they aim to incorporate electronic components into these materials so they can respond intelligently to changes in their environment.

“Going forward, we want to integrate active electronic materials into these woven structures so they can be ‘smart’ systems that can sense the external environment and morph their shapes in response to different application scenarios,” Filipov said.

Funding for this work came partly from the U.S. Air Force Office of Scientific Research (FA9550-22-1-0321).