Insect exoskeletons inspire better building materials

A design based on insect exoskeletons has helped a team of civil engineering researchers strike the balance between strength and damage tolerance in cement.

The project was led by Wenhui Duan, professor of structural 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 generally rigid and do not change shape when loaded with weight, says Wei Wang of Monash University, co-first author of the study.

“However, damage tolerance requires the material to deform under loading in order to dissipate energy.”

“Brittle materials”, such as concrete, are generally strong but break easily. If only a small area of ​​concrete cracks, the whole structure can quickly fail.

Strong, durable and environmentally friendly cement-like composite could be the building material of the future. Credit: Xinzheng/Moment/Getty Images.

As with so many things, however, nature has already found an effective way to balance these competing factors.

“If we think of evolution as a process of optimization, this optimization has been happening for millions of years,” says Wang’s co-first author, Shujian Chen, senior lecturer in structural engineering at the University of Queensland. .

An insect’s exoskeleton, especially its segmented legs, is both strong and capable of absorbing a lot of energy, making it tolerant of damage.

“Fleas have an incredible skill that allows them to jump up to 150 times their own length – it’s like a human jumping over 300 meters,” says Wang. “This requires that the exoskeleton not only sustain significant impact, but also absorb or release substantial energy.”

“We found that the insect exoskeleton has an asymmetric rotation mechanism that can achieve good strength and damage tolerance,” Chen says.

Inspired by nature, the team set to work developing a material design that would use this asymmetrical rotation to create a strong yet damage-tolerant building material.

Their invention combines a 3D printed polymer scaffold with cement to form a segmented honeycomb structure.

Mechanical tests showed that the material has high compressive strength – about 200% higher than aerated aerated concrete.

New building material illustration of 3d printed segmented honeycomb polymer structure and concrete-like building material
An illustration of the segmented honeycomb structure of the new building material. Image courtesy of Wenhui Duan.

“The amazing idea behind [this] breakthrough is actually to do [the material] weaker at times,” says Chen.

Creating such controlled weak points allows the material to undergo the same asymmetrical 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 conventional concrete does.

“We can contain the damage in a particular region of the material, while the rest of the structure can still maintain [its] integrity and most (about 80%) of the [its] bearing capacity,” says Duan.

With cement production currently contributing around 8% of global carbon dioxide emissions, the new design highlights a promising avenue for creating safer and more sustainable building materials that will also help 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 drastically reduce the amount of cement used, of course we can drastically 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 inspire more interest in civil engineering, which is generally considered a bit rudimentary and perhaps less exciting than other engineering disciplines.

“This article demonstrates the application of 3D printing, robotics, artificial intelligence – how these emerging technologies can transform the civilian [engineering] so that we can prepare our next generation of engineers,” he says.