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Tubulane-like polymer structures created at Rice University were better able to handle the impact of a bullet than the polymer reference cube on the bottom right

Researchers develop 3D-printed plastic cubes that repel bullets

Image credit: Jeff Fitlow | Rice University

Researchers in the US have 3D printed lightweight plastic structures that have hardness properties similar to diamond and are capable of enduring the impact of a bullet.

The team, from Rice University’s Brown School of Engineering in Texas, are testing polymers based on tubulanes, theoretical structures of crosslinked carbon nanotubes predicted to have extraordinary strength.

The Rice lab of materials scientist Pulickel Ajayan found tubulanes can be mimicked as scaled-up, 3D-printed polymer blocks that prove to be better at deflecting projectiles than the same material without holes. These blocks are also highly compressible without breaking apart.

Tubulanes were predicted in 1993 by chemist Ray Baughman of the University of Texas at Dallas and physicist Douglas Galvão of the State University of Campinas, Brazil, both co-principal investigators on the new paper. Tubulanes themselves have yet to be made, but their polymer cousins may be the next best thing.

Rice graduate student Seyed Mohammad Sajadi and his colleagues built computer simulations of various tubulane blocks, printed the designs as macroscale polymers and then subjected them to crushing forces and speeding bullets. The best proved to be 10 times better at stopping a bullet than a solid block of the same material.

The Rice team fired projectiles into patterned and solid cubes at a speed of 5.8km per second and, following the experiment, Sajadi said the results were impressive. “The bullet was stuck in the second layer of the structure,” he said. “But in the solid block, cracks propagated through the whole structure.”

Tests in a lab press showed how the porous polymer lattice lets tubulane blocks collapse in upon themselves without cracking, Sajadi added.

The Ajayan group made similar structures two years ago when it converted theoretical models of schwarzites (carbon structures) into 3D-printed blocks. However, Sajadi explained that the new work is a step toward what materials scientists consider a “holy grail”.

“There are plenty of theoretical systems people cannot synthesize,” he said. “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.”

According to Sajadi, tubulane-like structures of metal, ceramic and polymer are only limited by the size of the printer. He added that optimising the lattice design could lead to better materials for civil, aerospace, automotive, sports, packaging and biomedical applications.

The tubulane-inspired 3D printed structure was less impacted by a bullet than a cube of pure polymer

The tubulane-inspired 3D printed structure was less impacted by a bullet than a cube of pure polymer

Image credit: Jeff Fitlow | Rice University

“The unique properties of such structures comes from their complex topology, which is scale-independent,” said Rice alumni Chandra Sekhar Tiwary, co-principal investigator on the project. “Topology-controlled strengthening or improving load-bearing capability can be useful for other structural designs as well.”

According to co-authors Peter Boul and Carl Thaemlitz of Aramco Services Co, a sponsor of the research, potential applications span many industries, but oil and gas will find tubulane structures particularly valuable as tough and durable materials for well construction.

Furthermore, such materials must withstand impacts, particularly in hydraulic fracturing, that can rubblise (reducing existing concrete into rubble at its current location rather than hauling it to another location) standard cements.

“The impact resistance of these 3D-printed structures puts them in a class of their own,” Boul said.

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