Cut open a bone and you’ll see a subtly disordered structure. Tiny beams, called trabeculae, connect to one another in irregular patterns, distributing stress and lending bones an impressive toughness. What if human-made materials could exhibit similar properties?
In a new paper in Proceedings of the National Academy of Sciences Nexus, researchers at Penn’s School of Engineering and Applied Science, the School of Arts & Sciences, and Aarhus University found that adding just the right amount of disorder to the structure of certain materials can make them more than twice as resistant to cracking.
Until this point, one of the greatest challenges posed by mechanical metamaterials has been their fragility.“ Toughness is a limiting factor in not all, but many 3D-printed mechanical metamaterials,” says Kevin Turner, professor and John Henry Towne Department Chair of Mechanical Engineering and Applied Mechanics (MEAM) at Penn Engineering and the paper’s senior author.
This new result promises to address this issue and at relatively low cost. “Without changing the material at all, just simply by altering the internal geometry,” says Turner, “you can increase the toughness by 2.6 times.”
To test whether disorder makes mechanical metamaterials tougher, the researchers performed thousands of computational mechanics simulations of numerous different patterns, all based on a triangular lattice, called a truss. In some, the triangles were arranged in perfect symmetry, while in others, the pattern had been perturbed by moving the nodes where the triangles meet.
The team subjected the patterns to rounds of computer simulations and created physical versions of a representative set of geometries, including both ordered geometries and those with varying levels of disorder.
When they attempted to break the materials—in the lab and in the simulations—a clear trend emerged. “There was a specific level of disorder, so that the patterns we cut into the material looked somewhat regular but not exactly symmetrical, where we were able to achieve the highest level of performance,” says Fulco.
Read more at Penn Engineering Today.
