Researchers at Rice University have demonstrated that tubulanes, a type of theoretical, crosslinked carbon nanotube structure, can be built from everyday polymers and exhibit structural properties that make them harder than diamond.
Since first being theorized by Ray Baughman in 1993, tubulanes have excited the imagination of chemical and structural engineers due to their extraordinary hardness properties. But, until recently, the production of these materials has been elusive because of the difficulties in manufacturing long chains of carbon nanotubes.
However, Rice researchers have pulled an end-run around this production roadblock and 3D printed a polymer version of tubulanes that exhibits similar properties to their carbon nanotube antecendents.
According to Chandra Sekhar Tiwary, an investigator on the project “The unique properties of [tubulanes] comes from their complex topology, which is scale-independent.”
While somewhat difficult to describe, tubulane geometry consists of a crosslinked patchwork of lattices that are tightly woven yet still porous and flexible. This porosity and flexibility create a matrix across which great force can be distributed and dissipated, making them much stronger than a single unified mass of a single material.
In tests of their polymer tubulanes, Rice researchers fired bullets travelling 5.8 km/s into blocks of scaled up tubulane structures as well as solid blocks made of the same material. The results were immediately evident. Upon comparison, the tubulane structures were capable of stopping the force of projectiles, while their solid counterparts were crushed by the same force.
"The bullet was stuck in the second layer of the structure," xaid Seyed Mohammad Sajadi, a Rice University grad student and lead author on the paper detailing the findings. "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.
The validation that tubulanes are in fact very hard, and the discovery that they are relatively easy and inexpensive to make via 3D printing has drawn immediate attention from industry, where solutions for durable materials are always in high demand.
Rice University graduate student Seyed Mohammad Sajadi and his colleagues built computer simulations of tubulane blocks, printed the designs as macroscale polymers and subjected them to crushing forces and speeding bullets. (Image courtesy of Jeff Fitlow/Rice University.)
“The unique properties of such structures comes from their complex topology, which is scale-independent,” said Chandra Sekhar Tiwary, co-principal investigator on the project and now 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.”
According to Sajadi, tubulane-like structures made of metal, polymer or ceramic are limited only by the size of the printer used to build them, and by optimizing the lattice design these tubulane materials could become better options for aerospace and automotive, civil engineering, sports gear and could even find applications in the biomedical industry.
Engineers in the oil and gas industry see printable, polymer tubulanes as a material that could improve the environmental safety parameters associated with hydraulic fracturing, and co-authors Peter Boul and Carl Thaemlits are examining whether the material could be used in well construction.
“The impact resistance of these 3D-printed structures puts them in a class of their own,” said Peter Boul of Aramco Services, a sponsor of the Rice study.