Nov 14 2019
Diamond is the hardest known material. But a lightweight material full of holes is almost as hard as diamonds, as evidenced by the mere dents marked by speeding bullets.
Tubulane-like polymer structures created at Rice University were better able to handle the impact of a bullet than the polymer reference cube at the bottom right. The bullet stopped in approximately the second layer of the tubulane structures, with no significant structural damage observed beyond that layer. Bullets fired at the same speed sent cracks through the entire reference cube. Image Credit: Jeff Fitlow.
Scientists from the Brown School of Engineering of Rice University and their collaborators are analyzing polymers based on tubulanes. Tubulanes are hypothetical structures of cross-linked carbon nanotubes projected to have incredible strength.
Pulickel Ajayan, a materials scientist from the Rice lab, discovered that these structures of carbon nanotubes could be imitated as scaled-up, 3D-printed polymer blocks that have been demonstrated to be better at deflecting projectiles when compared to the same material that lacks holes. Moreover, the blocks do not break apart even when they are highly compressed.
As illustrated in the Small journal, this finding can potentially lead to the development of different sizes of printed structures that have tunable mechanical characteristics.
Chemist Ray Baughman from the University of Texas at Dallas along with physicist Douglas Galvão from the State University of Campinas, Brazil, had predicted tubulanes in 1993. Both are co-principal investigators of the recent article. While tubulanes have not been developed yet, their polymer cousins could provide the next best option.
Seyed Mohammad Sajadi, the study lead author and Rice graduate student, and his collaborators created computer simulations of different tubulane blocks. They then printed the designs as macroscale polymers and ultimately subjected them to speeding bullets and crushing forces.
At best, these polymers proved to be 10 times better at preventing a bullet when compared to a solid block of the same material.
The Rice researchers also fired projectiles into solid and patterned cubes at 5.8 km per second. According to Sajadi, the results were quite remarkable.
The bullet was stuck in the second layer of the structure. But in the solid block, cracks propagated through the whole structure.
Seyed Mohammad Sajadi, Study Lead Author and Graduate Student, Rice University
Tests carried out in a laboratory press demonstrated how the porous polymer lattice allows the tubulane blocks to collapse upon themselves without breaking apart, added Sajadi.
Two years ago, the Ajayan team created analogous structures when it changed hypothetical prototypes of schwarzites into 3D-printed blocks. However, the latest study represents a step toward what materials researchers consider a holy grail, informed Sajadi.
There are plenty of theoretical systems people cannot synthesize. 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.
Seyed Mohammad Sajadi, Study Lead Author and Graduate Student, Rice University
According to Sajadi, tubulane-like structures of polymer, ceramic, and metal are only restricted by the printer size. Improving the lattice design can result in better materials for biomedical, packaging, sports, automotive, aerospace, and civil applications, he added.
The unique properties of such structures comes from their complex topology, which is scale-independent. Topology-controlled strengthening or improving load-bearing capability can be useful for other structural designs as well.
Chandra Sekhar Tiwary, Co-Principal Investigator, Rice University
Tiwary is a Rice alumnus and currently an assistant professor at the Indian Institute of Technology, Kharagpur.
Co-authors Carl Thaemlitz and Peter Boul of Aramco Services Co., which sponsored the study, stated that potential applications cover a number of industries, but the oil and gas industry will find the tubulane structures specifically useful as strong and long-lasting materials for construction of wells. Materials like these should endure impacts, specifically in hydraulic fracturing, that can rubblize regular cements.
“The impact resistance of these 3D-printed structures puts them in a class of their own,” stated Boul.
Study co-authors include graduate student Prathyush Ramesh and research scientist Muhammad Rahman of Rice University; Rice alumnus Cristiano Woellner, an assistant professor at the Federal University of Parana, Brazil; and Rice alumnus Shannon Eichmann and Qiushi Sun of the Aramco Research Center, Houston.
Ajayan is chair of the Department of Materials Science and NanoEngineering at Rice University, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering, and a professor of chemistry.
The study was supported by the Brazilian National Council for Scientific and Technological Development and the São Paulo Research Foundation.
Theoretical tubulanes inspire ultra hard polymers
A compression test showed that tubulane-based materials developed at Rice University handled pressure well, collapsing without cracking. Video Credit: The Ajayan Research Group/Rice University.