Inspired by the architecture of human bone’s tough outer layer, engineers at Princeton have developed a cement-based material that’s 5.6 times more damage-resistant than standard counterparts. The bio-inspired design allows the fabric to withstand cracking and avoid sudden failure, unlike conventional, brittle cement-based counterparts.
In a Sept. 10, article within the journal Advanced Materials, the research team led by Reza Moini, an assistant professor of civil and environmental engineering, and Shashank Gupta, a third-year Ph.D. candidate, show that cement paste deployed with a tube-like architecture can significantly increase resistance to crack propagation and improve the flexibility to deform without sudden failure.
“Certainly one of the challenges in engineering brittle construction materials is that they fail in an abrupt, catastrophic fashion,” Gupta said.
In brittle construction materials utilized in constructing and civil infrastructure, strength ensures ability to sustain loads, while toughness supports resistance to cracking and spread of injury within the structure. The proposed technique tackles those problems by creating a cloth that’s tougher than conventional counterparts while maintaining strength.
Moini said the important thing to the development lies within the purposeful design of internal architecture, by balancing the stresses on the crack front with the general mechanical response.
“We use theoretical principles of fracture mechanics and statistical mechanics to enhance materials’ fundamental properties ‘by design’,” he said.
The team was inspired by human cortical bone, the dense outer shell of human femurs that gives strength and resists fracture. Cortical bone consists of elliptical tubular components often called osteons, embedded weakly in an organic matrix. This unique architecture deflects cracks around osteons. This prevents abrupt failure and increases overall resistance to crack propagation, Gupta said.
The team’s bio-inspired design incorporates cylindrical and elliptical tubes inside the cement paste that interact with propagating cracks.
“One expects the fabric to change into less proof against cracking when hole tubes are incorporated,” Moini said. “We learned that by benefiting from the tube geometry, size, shape, and orientation, we will promote crack-tube interaction to reinforce one property without sacrificing one other.”
The team discovered that such enhanced crack-tube interaction initiates a stepwise toughening mechanism, where the crack is first trapped by the tube after which delayed from propagation, resulting in additional energy dissipation at each interaction and step.
“What makes this stepwise mechanism unique is that every crack extension is controlled, stopping sudden, catastrophic failure,” said Gupta. “As an alternative of breaking unexpectedly, the fabric withstands progressive damage, making it much tougher.”
Unlike traditional methods that strengthen cement-based materials by adding fibers or plastics, the Princeton team’s approach relies on geometric design. By manipulating the structure of the fabric itself, they achieve significant improvements in toughness without the necessity for added material.
Along with improving fracture toughness, the researchers introduced a brand new method to quantify the degree of disorder, a crucial quantity for design. Based on statistical mechanics, the team introduced parameters to quantify the degree of disorder in architected materials. This allowed the researchers to create a numerical framework reflecting the degree of disorder of the architecture.
The researchers said the brand new framework provides a more accurate representation of the fabric’s arrangements, moving towards a spectrum from ordered to random, beyond the easy binary classifications of periodic and non-periodic. Moini said that the study makes a distinction with approaches that confuse irregularity and perturbation with statistical disorder corresponding to Voronoi tessellation and perturbation methods.
“This approach gives us a robust tool to explain and design materials with a tailored degree of disorder,” Moini said. “Using advanced fabrication methods corresponding to additive manufacturing can further promote the design of more disordered and mechanically favorable structures and permit for scaling up of those tubular designs for civil infrastructure components with concrete.”
The research team has also recently developed techniques allowing for an amazing deal of precision using robotics and additive manufacturing. By applying them to recent architectures, and combos of hard or soft materials inside the tubes, they hope to expand the further the chances of applications in construction materials.
“We have only begun to explore the chances,” Gupta said. “There are various variables to analyze, corresponding to applying the degree of disorder to the dimensions, shape, and orientation of the tubes in the fabric. These principles could possibly be applied to other brittle materials to engineer more damage-resistant structures.”
