In order to explore better materials, scientists continue to improve existing materials, seeking more new possibilities to give them the characteristics they lack. This time, researchers at the Massachusetts Institute of Technology (MIT) in the United States have developed a new manufacturing method that may allow previously fragile materials such as ceramics, glass, and semiconductors to acquire tensile properties.
In the past, the development of metamaterials has focused on maintaining low density while making the internal lattice structure harder and more resistant to compression. However, the internal joints and nodes were fragile, prone to cracking during stretching or elongation processes, severely affecting overall performance.
Although the scientific community has successfully suppressed crack propagation, enhanced material rigidity and tensile properties through methods such as lattice interpenetration, spiraling, and lattice weaving, a trade-off between rigidity and tensile properties has limited the potential performance of metamaterials.
To address this issue, engineers at MIT have used materials used in making adhesives to create flexible and rigid polymers separately, and combined them using a dual-network (DN) approach to make them both strong and elastic, becoming a mechanical metamaterial that does not sacrifice its original properties. This research was published in the journal “Nature” on April 23.
Metamaterials, also known as metamaterials, refer to engineered materials with unique properties not found in nature. Although there is nothing special about the composition of metamaterials, their unique properties stem from a large number of extremely small special geometric structures.
The MIT experimental team used high-precision laser 3D printing to print nano-scale micro lattices of acrylic ester polymers with characteristics similar to organic glass and ceramics, and used a single-frame truss as a “skeleton” for the flexible material to be woven on top, integrated into a “dual network” structure.
The researchers found that although the material they used was as hard as organic glass itself, the resulting woven metamaterial was as soft and elastic as rubber, combining both flexibility and rigidity.
They also conducted a series of pressure tests on the material and found that the “dual-network” metamaterial had higher rigidity and stretching than pure materials, even being able to stretch up to 10 times its original length without complete fracturing. In comparison, other forms of polymers had almost no stretch and were prone to breaking during stretching.
The researchers stated that the material’s resistance to stretching comes from the interaction between the rigid pillars and the chaotic coiling weave when the material is under pressure and stretching. As fractured pillars produce more entanglement, winding around the rigid lattice, allowing the overall structure to withstand greater pressure.
Furthermore, the experimental team found that strategically introducing some “defects” into the metamaterial could make the “dual-network” metamaterial more elastic and tear-resistant than before. The team also developed a computational framework that allows engineers to design anti-tear textiles based on the performance of metamaterials.
The researchers said that the new dual-network design could be applied to other materials, including elastic ceramics, glass, and metals, or be used to create tear-resistant textiles, flexible semiconductors, electronic chip packaging, and even for cultivating cell tissues with repair properties in the future.
They also plan to make this dual-network metamaterial reactive to electricity or temperature. For example, creating a fabric that changes breathability and softness when warm and becomes harder when cold.
Carlos Portela, Assistant Professor of Career Development in the Department of Mechanical Engineering at MIT, said, “In the past, we have been looking for the hardest and most robust metamaterials, without trying to apply them to soft materials. Now the team is pioneering this new field for metamaterials, planning to print metals or ceramics using the dual-network approach to obtain better materials.”
Portela explained, “You can imagine this dual-network metamaterial as a bunch of spaghetti wrapped around a grid. When we damage the grid network, these spaghetti strands will entangle with the fragments of the grid, forming more entanglements that make the material stronger.”
The first author of the study, postdoctoral scholar James Utama Surjadi, said, “You might think that adding defects would degrade the material, but we actually found that these defects could double the stretching capacity of metamaterials and triple their energy dispersion capability.”
Portela added, “We plan to apply this method to more brittle materials to give them multifunctionality.”
This research was partially funded by the National Science Foundation and the MechE MathWorks Seed Fund at MIT.