A design based on insect exoskeletons has helped a team of civil engineers crack the balance between strength and damage tolerance in cement.
The project was led by Wenhui Duan, a professor of civil engineering at Monash University, and described in an article published in nature communication Last month.
The trade-off between a material’s strength—its ability to support weight—and its ability to tolerate damage is a classic engineering dilemma.
High-strength materials are typically stiff and don’t change shape when loaded with weight, explains Wei Wang of Monash University, who is co-first author of the study.
“However, damage tolerance requires the material to deform under stress to dissipate energy.”
So-called “brittle materials” like concrete tend to be strong but break easily. If just a small area of concrete cracks, the entire structure can quickly fail.
However, as in so many things, nature has already found a successful way to balance these competing factors.
“If we look at evolution as an optimization process, that optimization has been happening for millions of years,” says Wang’s co-first author Shujian Chen, lecturer in civil engineering at the University of Queensland.
An insect’s exoskeleton – specifically its segmented legs – is both strong and capable of absorbing large amounts of energy, making it damage tolerant.
“Fleas have an amazing ability that allows them to jump up to 150 times their own length — that’s like a human jumping 300 meters,” says Wang. “It requires that the exoskeleton not only withstand a significant impact, but also absorb or release significant energy.”
“We found that the insect exoskeleton has an asymmetric rotation mechanism, which can achieve good strength and damage tolerance,” explains Chen.
Inspired by nature, the team set to work developing a material design that takes advantage of this asymmetric rotation to create a strong yet damage-tolerant build material.
Their invention combines a 3D-printed polymer scaffold with cement to form a segmented honeycomb structure.
Mechanical tests showed that the material had a high compressive strength – about 200% higher than aerated concrete.
“The amazing idea behind it [this] A breakthrough is actually to be made [the material] weaker in some places,” explains Chen.
The creation of such controlled vulnerabilities allows the material to experience the same asymmetric rotation as the insect’s exoskeleton.
The new design also means that if the material is damaged, it will fail layer by layer rather than all at once like traditional concrete.
“We can contain the damage in a specific area of material while the rest of the structure still remains [its] Integrity and most (around 80%). [its] Carrying capacity,” explains Duan.
With cement production currently contributing an estimated 8% of global carbon emissions, the new design shows a promising path to creating safer and more durable building materials that also benefit the environment.
Chen explains that because cement is brittle, engineers typically use 30% more material than is technically required to make the structure safer.
“So if we can significantly reduce cement consumption, then of course we can also significantly reduce carbon dioxide emissions globally,” he says.
The concepts behind the design can be applied to other brittle materials such as glass and ceramics.
Duan also hopes the research will spark more interest in civil engineering, which is typically viewed as a bit low-tech and perhaps less exciting than other engineering disciplines.
“This paper demonstrates the application of 3D printing, robotics and artificial intelligence – how these new technologies can transform the civil world [engineering] so we can prepare our next generation of engineers,” he says.