A study published in Proceedings of the National Academy of Sciences Nexus by researchers from Penn Engineering, the University of Pennsylvania School of Arts & Sciences, and Aarhus University shows that incorporating controlled disorder into the structure of certain materials can enhance their resistance to cracking.
The findings underscore the potential to advance mechanical metamaterials—engineered materials with precise geometric designs that impart unique physical and mechanical properties, fabricated through 3D printing. This discovery addresses one of the key challenges of these materials: their fragility. “By simply altering the internal geometry, without changing the material itself, toughness can be increased by 2.6 times,” said Kevin Turner, Professor, Penn Engineering.
This research was made possible with help from the National Science Foundation (NSF) MRSEC program, which supports interdisciplinary research in materials science, the National Defense Science & Engineering Graduate Fellowship Program which supports graduate students pursuing advanced degrees in STEM disciplines, and the Villum Foundation, a private philanthropic organization based in Denmark.
Research on How Disorder Toughens Materials
The researchers explored how small-scale disorder influences material performance, taking inspiration from natural materials like bone, nacre, and mussel threads, which exhibit minute, seemingly random variations. With this in mind, the team conducted computational simulations on various triangular lattice patterns, including both symmetrical designs and those with variations in node positions.
Lab and simulation tests revealed that the best-performing samples, where cracks were hardest to propagate, had varied geometries. “The samples that performed the best, in which it was most difficult for a crack to grow, did not consist of regular repeating patterns. They had different geometry in different areas,” said Sage Fulco, Lead Author and Postdoctoral Researcher, MEAM.
The study also identified an optimal level of disorder—too little or too much led to less effective performance. “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.
Future Prospects: Expanding the Potential of Disordered Patterns
Looking ahead, the researchers hope to inspire further exploration of disordered patterns in mechanical metamaterials and engineering. They emphasize that the success of their design reveals the untapped potential of studying natural materials, with applications in critical sectors like aerospace, where crack resistance and damage tolerance are vital. “Combining diverse materials and integrating geometries across multiple scales offers exciting opportunities,” says Fulco.
Advancements in 3D Printing for Enhanced Material Resistance
Recent innovations in 3D printing aim to improve material strength and resistance through bio-inspired designs and advanced techniques. In 2022, a team from the Southern University of Science and Technology in China, the School of Metallurgy and Materials at the University of Birmingham, UK, the Hong Kong University of Science and Technology, Peking University Shenzhen Hospital, and the HKUST Shenzhen-Hong Kong Collaborative Innovation Research Institute developed 3D-printed ceramic composites with enhanced toughness. By integrating mantis shrimp-inspired structures with digital light processing (DLP) 3D printing, the team sought to overcome the limitations of traditional methods like ice templating and freeze casting.
Elsewhere, researchers from the City University of Hong Kong (CityU), developed a method to make 3D-printed polymeric lattice parts 100 times stronger. By partially carbonizing the material, they achieve both increased strength and improved ductility, enabling the creation of customized, durable prints for applications like coronary stents and bio-implants. This process offers a cost-effective, scalable solution for producing lightweight, strong, and versatile mechanical metamaterials.
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Featured image shows the disordered design (bottom) cracked less than the structured one (top), shown by the spread of red dots. Image via: Sage Fulco
