Researchers at Rice University’s Brown School of Engineering have 3D printed lightweight plastic structures that have hardness properties similar to diamond. In an impressive experiment, the team shot bullets at the cubic 3D printed structures with barely any effect.
How have the researchers created bulletproof plastic cubes? The answer is tubulanes, which are theoretical structures of crosslinked carbon nanotubes. These structures are predicted to have incredible strength, and the research team was interested in exploring how they could be applied in the physical world with polymers.
Materials scientist Pulickel Ajayan discovered that though real tubulanes have not yet been made, they could be recreated in a scaled up form using 3D printing and polymer materials. Lead author of the research Seyed Mohammad Sajadi and his colleagues generated computer simulations of tubulane blocks, scaled them up and 3D printed them using polymer materials.
The researchers then compared the 3D printed structures to blocks made entirely of the same material (without porous geometries) by conducting a range of tests. In all the tests—which included crushing them and shooting bullets at them—the 3D printed tubulane-inspired blocks performed significantly better.
In the bullet test, where projectiles were fired at a speed of 5.8 km per second, the 3D printed block was 10 times better at stopping a bullet than a solid block made up of the same plastic. “The bullet was stuck in the second layer of the structure,” Sajadi said. “But in the solid block, cracks propagated through the whole structure.”
A lab press test conducted by the researchers (seen in the video below) also demonstrated how the 3D printed lattice collapse on itself without cracking, while the solid block succumbed to cracking. The results of these tests show the potential of printing structures of any size with tunable mechanical properties and extraordinary strength. In the realm of materials science, the research is an exciting step towards producing actual tubulanes.
“There are plenty of theoretical systems people cannot synthesize,” Sajadi explained. “They’ve remained impractical and elusive. But with 3D printing, we can still take advantage of the predicted mechanical properties because they’re the result of the topology, not the size.”
“The unique properties of such structures comes from their complex topology, which is scale-independent,” added Rice alumnus Chandra Sekhar Tiwary, co-principal investigator on the project and an assistant professor at the Indian Institute of Technology, Kharagpur. “Topology-controlled strengthening or improving load-bearing capability can be useful for other structural designs as well.”
In various industries where additive manufacturing is being adopted, there is a keen interest about the potential of metamaterials or internal lattices. By exploiting the strength of tubulane structures using AM, new printable structures made from metal, ceramic or plastics can be designed in various sectors.
A particularly interesting industry for printed tubulane structures is oil and gas, which could benefit from the strength of materials for well construction, which requires extreme impact resistance.