When you hear about designers biomimicking butterflies, your first thought is probably about creating remote-controlled flying toys or small, artificial flying machines that could be useful in pollination, especially in regions experiencing bee colony collapse. But butterfly mimicry goes far beyond those uses to include scattering light to replace toxic paints or as an anti-fraud mechanism against counterfeiters, advancing optical computing, and even creating superior eye implants.
And it now also includes making buildings.
Because when you think of designing massive, heavy, structures that require durability to withstand hundreds of tons of pressure from people, furniture, equipment, and their own components – not to mention the stresses of wind and the potential for earthquakes – why wouldn’t you immediately think of applying the structure of the tiny, delicate, organic stained-glass windows that we call butterfly wings?
In their International Journal of Mechanical Sciences paper, Jing Wei, Xiao Wong, and colleagues at Wuhan University of Technology in China, and Eric Jianfeng Cheng at Japan’s Tohoku University, explain how despite the low-mass and high energy-absorbing design value of traditional lattices, their vulnerability is in stress concentration.
One hit in the wrong place and boom! – total collapse and disaster. To counter that shatterability, the researchers applied the uniform stress distribution of butterfly wings to architecture, using a butterfly-inspired body-centered cubic (BCCB) topology (shapes that can sustain twisting or stretching).
The superpower of this design, which increases its ability to absorb energy and resist impact, is its anisotropic lattice. In anisotropy, the opposite of isotropy, a structure isn’t uniform in all directions. Think of a tree – hit a cut section of it with an axe along the grain of its wood, and it easily splits. Hit that tree with that same axe against the grain, and it takes forever to make it fall. Polarized lenses, crystals, steel polymers, and 3D-printed objects are all anisotropic, whereas a rubber ball or the contents of a glass of water are isotropic.
By applying anisotropy to architecture, the designers achieve controlled deformation and, during compression, non-destructive stress redistribution. As Chen explains, “This structural mechanism is particularly remarkable, since most lightweight lattice materials aren't able to withstand forces like local buckling or shock. In contrast, our design shows a much greater resistance to sudden mechanical loading.”
If the researchers continue achieving useful results with anisotropic designs, their aim is applying its strength and light weight to designing automobiles, aircraft, and even spacecraft, and of course to creating earthquake-resistant infrastructure. The imperative for such innovation in that field is massive.
For instance, despite lasting only 20 seconds, the 1995 earthquake that struck Kobe, Japan destroyed 100,000 buildings, and the 2011 earthquake/tsunami that smashed Tōhoku, Japan killed more than 15,000 people and forced 130,000 to abandon their homes temporarily or permanently. The 2004 earthquake at the Sumatra-Andaman Islands initiated tsunamis, resulting in 280,000 deaths and 1.1 million people displaced across East African and South Asian countries.
Therefore, buildings employing the Wuhan and Tohoku anisotropic design offer great hope for preventing widespread injury and death during earthquakes, or quicker repairs and fewer abandoned homes. In both simulations and mechanical tests involving dynamic impact loading and quasi-static compression, the anisotropic designs significantly outperformed conventional lattices designs, and redistributed stress via deformation resembling a butterfly’s outstretched wings, thus preventing total collapse.
Source: Tohoku University
