A project based on insect exoskeletons helped a team of civil engineering researchers strike a balance between strength and damage tolerance in concrete.
The project was led by Wenhui Duan, professor of structural engineering at Monash University, and described in an article published in Nature communications last month.
The trade-off between a material’s strength – its ability to bear weight – and its ability to tolerate damage is a classic engineering dilemma.
High-strength materials are generally rigid and do not change shape when loaded with weight, explains Wei Wang of Monash University, co-first author of the study.
“However, damage tolerance requires the material to deform under load to dissipate the energy.”
So-called “brittle materials”, such as concrete, are generally strong but break easily. If only a small area of concrete cracks, the entire structure can fail quickly.
As in so many things, however, nature has already found an effective way to balance these competing factors.
We found that the insect exoskeleton has an asymmetrical rotation mechanism which can achieve good resistance and damage tolerance.
Shujian Chen, Professor of Structural Engineering at the University of Queensland.
“If we look at evolution as an optimization process, that optimization has been going on for millions of years,” says Shujian Chen, co-lead author of Wang, professor of structural engineering at the University of Queensland.
An insect’s exoskeleton – particularly its segmented legs – is strong and capable of absorbing a lot of energy, making it resistant to damage.
“Fleas have an amazing ability that allows them to jump up to 150 times their length, it’s like a human jumping over 300 meters,” says Wang. “It requires the exoskeleton not only to sustain a significant impact, but also to absorb or release significant energy.”
“We found that the insect exoskeleton has an asymmetrical rotation mechanism that can achieve good resistance and damage tolerance,” explains Chen.
Inspired by nature, the team began work on developing a material design that used this asymmetrical rotation to create a strong yet damage-resistant building material.
Their invention combines a 3D printed polymer scaffold with concrete to form a segmented honeycomb structure.
Mechanical tests showed that the material had a high compressive strength, about 200% higher than foam cellular concrete.
“The amazing idea behind it [this] the turning point is actually to be done [the material] weaker in some places, “explains Chen.
Creating such controlled weak spots allows the material to undergo the same asymmetrical rotation of the insect exoskeleton.
The new design also means that if the material is damaged, it breaks down layer by layer rather than all at once like conventional concrete does.
“We can contain the damage within a particular region of material, while the rest of the structure can still be maintained [its] integrity and most (about 80%). [its] load capacity, “explains Duan.
Chen explains that because concrete is brittle, engineers typically use 30 percent more material than is technically required to make the structure safer.
“So if we can significantly reduce the amount of cement used, we can obviously significantly reduce carbon dioxide emissions globally,” he says.
The concepts behind the design can be applied to other fragile materials, such as glass and ceramics.
Duan also hopes the research will spark more interest in civil engineering, which is generally seen as somewhat low-tech and perhaps less exciting than other engineering disciplines.
- This article is published in collaboration with Cosmos Magazine. Cosmos is produced by the Royal Institution of Australia to inspire curiosity in “The Science of Everything”. See cosmosmagazine.com.