Carbon nanotube fiber has the highest tensile strength and stiffness of any material, with multi-walled carbon nanotubes measuring 63 GPa. Bulk carbon nanotube fiber has a tensile strength of 1.6 GPa, making it the strongest fiber. The US Navy is interested in using it for ropes and ROVs, while it could also improve bridge strength and space exploration. The cost has dropped in recent years.
The material with the greatest tensile strength is carbon nanotube fiber. It’s also the stiffest material known, with a tremendously high modulus of elasticity, meaning it doesn’t stretch easily. Carbon nanotubes can be visualized as sheets of graphene curled into cylinders just one molecule wide.
These cylinders can have single walls (SWNTs or single wall carbon nanotubes) or multiple walls (MWNTs or multiwall carbon nanotubes). Multi-walled carbon nanotubes were measured to have the greatest tensile strength material of all, measuring 63 GPa (gigapascals) for atomic-scale testing, well below the theoretical maximum of 300 GPa. Scientists have not yet been able to produce this tensile strength in bulk materials, although work is ongoing and eventual success seems likely.
Unlike carbon nanotubes, high carbon steel has a tensile strength of approximately 1.2 GPa. The bulk carbon nanotube fiber was created with a tensile strength of 1.6 GPa, which is the highest tensile strength of any fiber, natural or man-made, by over an order of magnitude. Further improvements of another order of magnitude look plausible in the coming decades. The carbon nanotube fiber is so strong that a 50,000 km (31,070 miles) long cable of the fiber could be extended from the earth’s surface in a geosynchronous orbit and would not break. This concept is known as the space elevator.
In May 2007, US Navy-funded researchers succeeded in making carbon nanotubes longer than 2 mm, the longest ever made. The length-to-width ratio of these nanotubes is approximately 900,000 to 1. The Navy is understandably interested in fibers with the highest possible tensile strength, as they use ropes for numerous purposes such as mooring, cargo securing, etc. Stronger fibers would allow submerged ROVs (remotely operated vehicles) to weigh more, travel deeper and be more reliably tethered to their base stations, relevant in light of a $15 million Japanese ROV, among the most advanced in the world, which was recently lost in a severe storm. So the fibers with the greatest tensile strength would increase our ability to explore the ocean floor.
Similar benefits could ripple through all domains of engineering and design. Bridges could be made much stronger if carbon nanotube fiber became more affordable. It currently costs hundreds or thousands of dollars per gram, but the cost has dropped exponentially in recent years.
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