A study reveals that adding controlled disorder to materials can make them significantly tougher and more resistant to cracking, opening new pathways for advanced mechanical designs.
In a new study, researchers from Penn Engineering, Penn Arts & Sciences and Aarhus University have uncovered that introducing a controlled amount of disorder into the internal structures of materials can make them significantly tougher.
This finding, published in the Proceedings of the National Academy of Sciences Nexus, could pave the way for the broader application of mechanical metamaterials across various industries.
Nature-Inspired Toughness
The inspiration for this breakthrough came from nature. Materials like human bones and nacre (mother of pearl) feature irregular internal patterns that distribute stress and increase toughness.
The research team asked: What if man-made materials could emulate these natural properties?
The findings suggest they can. By adjusting the geometry of certain synthetic materials without changing their composition, the team was able to increase their toughness by a factor of 2.6.
This is a significant leap forward for mechanical metamaterials, which are known for their unique properties but often suffer from fragility issues.
“Toughness is a limiting factor in not all, but many 3D-printed mechanical metamaterials,” senior author Kevin Turner, a professor and John Henry Towne Department Chair of Mechanical Engineering and Applied Mechanics (MEAM) at Penn Engineering, said in a news release. “Without changing the material at all, just simply by altering the internal geometry, you can increase the toughness by 2.6 times.”
The Balance of Disorder
The research focused on experimenting with various levels of disorder within a material’s structure. They tested thousands of patterns using computational mechanics simulations, all based on triangular lattices called trusses. Some patterns maintained perfect symmetry, while others introduced varying degrees of irregularity.
Caption: In contrast to the more structured design (top), the more disordered one (bottom) cracked less easily, as evidenced by the dispersion of the red dots.
Credit: Sage Fulco
Lead author Sage Fulco, a postdoctoral researcher in MEAM, noted that the most effective designs were those that balanced order and chaos.
“The samples that performed the best, in which it was most difficult for a crack to grow, did not consist of regular repeating patterns,” Fulco said in the news release. “They had different geometry in different areas.”
Visualizing Success
To understand the mechanics behind their success, the team collaborated with Doug Durian, the Mary Amanda Wood Professor in Physics and Astronomy at Penn Arts & Sciences, and Hongyi Xiao, then a postdoctoral fellow in Durian’s lab.
They devised experiments to visualize how cracks propagated through the materials. Through birefringence — a property that splits light into different paths — they could see that cracks in disordered materials did not travel in straight lines. Instead, damage was dispersed over a larger area, preventing catastrophic failure.
“For the crack to grow through a disordered material, damage has to occur over a much larger area,” Fulco added.
Broad Implications
The study’s implications are far-reaching. By identifying a geometric method to enhance toughness, this research could enable the application of mechanical metamaterials in critical fields such as aerospace, where materials must resist crack growth and sustain damage.
As Fulco pointed out, “[T]his work is very fundamental. Other groups can apply it to many different geometries.”
Turner expressed similar enthusiasm about the future, adding: “We’re enabling broader use of mechanical metamaterials in structural applications by identifying a geometric route to increase toughness.”
Ultimately, the team hopes their findings will inspire a deeper exploration of disordered patterns in mechanical design, fostering innovation that could transform multiple industries. The discovery underscores a fundamental truth observed in nature: sometimes, disorder and complexity can lead to remarkable strength.