The innovative minds at Princeton have drawn inspiration from the resilient structure of human bones to create a groundbreaking cement-based material. This cutting-edge development boasts a remarkable 5.6 times increase in damage resistance compared to standard counterparts.
By mimicking the tough outer layer of human bones, this bio-inspired design equips the material with the ability to resist cracking and prevent sudden failure, setting it apart from conventional, brittle cement-based alternatives.
In the paper, the research team spearheaded by Reza Moini, an esteemed assistant professor of civil and environmental engineering, and the brilliant third-year Ph.D. candidate, Shashank Gupta, presents compelling evidence of the material’s enhanced performance.
Their demonstration reveals that the implementation of a tube-like architecture in cement paste significantly fortifies its resistance to crack propagation while simultaneously improving its capacity to deform without succumbing to abrupt failure.
“One of the challenges in engineering brittle construction materials is that they fail in an abrupt, catastrophic fashion,” Gupta said.
In the realm of brittle construction materials used in building and civil infrastructure, strength is the bedrock that ensures the ability to withstand loads, while toughness serves as the shield against cracking and the spread of damage within the structure. The innovative technique we propose takes on these challenges by creating a material that not only maintains strength but also surpasses conventional counterparts in toughness.
Moini asserts that the key to this advancement lies in the deliberate design of internal architecture, effectively balancing the stresses at the crack front with the overall mechanical response.
“We use theoretical principles of fracture mechanics and statistical mechanics to improve materials’ fundamental properties ‘by design,’” he said.
The team drew inspiration from the remarkable strength and fracture resistance of human cortical bone, particularly the dense outer shell found in human femurs. This unique bone structure, made up of elliptical tubular components called osteons, is embedded within an organic matrix and has the remarkable ability to deflect cracks around osteons, preventing sudden failure and increasing overall resistance to crack propagation, as explained by Gupta.
Building on this natural wonder, the team’s bio-inspired design integrates cylindrical and elliptical tubes within the cement paste, strategically interacting with propagating cracks to enhance resilience and durability.
“One expects the material to become less resistant to cracking when hollow tubes are incorporated,” Moini said. “We learned that by taking advantage of the tube geometry, size, shape, and orientation, we can promote crack-tube interaction to enhance one property without sacrificing another.”
The team has made a groundbreaking discovery that has the potential to revolutionize material toughness. By enhancing crack-tube interaction, they have unlocked a stepwise toughening mechanism that traps and delays cracks from propagating, resulting in additional energy dissipation at each interaction and step.
“What makes this stepwise mechanism unique is that each crack extension is controlled, preventing sudden, catastrophic failure,” said Gupta. “Instead of breaking all at once, the material withstands progressive damage, making it much tougher.”
Unlike traditional methods that rely on adding fibers or plastics to strengthen cement-based materials, the Princeton team’s approach focuses on manipulating the material‘s structure. This innovative technique has led to substantial improvements in toughness without the need for additional materials.
In addition to enhancing fracture toughness, the researchers have introduced a novel method to quantify the degree of disorder, a crucial factor in design. Utilizing statistical mechanics, the team has developed parameters to measure the degree of disorder in architected materials, establishing a numerical framework to reflect the architecture’s disorder level.
The researchers have unveiled a groundbreaking framework that revolutionizes our understanding of material structures, transcending traditional classifications. This new approach offers a more accurate representation, encompassing a spectrum from ordered to random, going beyond simplistic binary distinctions. Moini, one of the researchers, emphasized the distinction from other methods that tend to conflate irregularity with statistical disorder.
“This approach gives us a powerful tool to describe and design materials with a tailored degree of disorder,” Moini said. “Using advanced fabrication methods such as additive manufacturing can further promote the design of more disordered and mechanically favorable structures and allow for scaling up of these tubular designs for civil infrastructure components with concrete.”
Furthermore, the research team has pioneered cutting-edge techniques leveraging robotics and additive manufacturing to achieve unparalleled precision. Their goal is to explore new architectural designs and combinations of materials within the tubes, aiming to unlock a myriad of possibilities for applications in construction materials.
“We’ve only begun to explore the possibilities,” Gupta said. “There are many variables to investigate, such as applying the degree of disorder to the size, shape, and orientation of the tubes in the material. These principles could be applied to other brittle materials to engineer more damage-resistant structures.”
Journal reference:
- Shashank Gupta, Reza Moini. Tough Cortical Bone-Inspired Tubular Architected Cement-Based Material with Disorder. Advanced Materials, 2024; DOI: 10.1002/adma.202313904