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January 21, 2009

Cambridge Making Carbon Nanotubes Ribbons at Centimeter Lengths with 9 Gpa Strength, Which is Four Times Stronger than Kevlar

The Times UK reported claims that Alan Windle's team at Cambridge University had created the world’s strongest ribbon. I finally tracked down specifics of this work.

UPDATE: Details on hypersonic skyhooks/rotovators [orbital ropes] that would be enabled with these materials as well as lunar and Mars space elevators.

Background on strength of materials, units of measure and the historical progress in improving strength of materials

From a press release of the 2nd International Conference on Space Elevator and Carbon Nanotube Tether Design in Luxembourg on Dec 14, 2008 Cambridge is making 9 Gpa strength material with a density of one gram per cc [same density as water] and believe that they can increase the strength to 10 GPa and make it in meter lengths in time for a space elevator tether competition in late April, 2009. [Competition tethers must be 2 meters long and a maximum of 2 grams.] They are also scaling this up to industrial scale over the next few years. Space elevators are closer as well as other tether applications like orbital skyhooks. Industrial scale at 10GPa means lighter, stronger cars, planes, bikes, spaceships, armor. If they can control the electrical properties then you can transform the electric grid and wiring. Key parts of the populist vision of molecular nanotechnology would be happening when this is scaled to industrial levels.

Prof. Windle’s research team at the University of Cambridge seems to lead the way towards super strong tethers. As Cambridge researcher Dr. Marcelo Motta pointed out they are currently able to produce almost cm long individual macroscopic CNT threads with tensile strength of up to 9 N/tex which compares to about 9 GPa at the given density of their material. Scaling up the Cambridge laboratory process to industrial production and spinning these threads, ropes and cables with 10 GPa should be soon feasible. As a possible next step Dr. Motta announced the likely participation of the Cambridge team in the coming Strong Tether Challenge hosted by NASA/Spaceward in 2009, as explained by Dr. Bryan Laubscher of Odysseus Technologies.


The Cambridge material is two and half times stronger than Spectra 2000 and Zylon which are used for bullet proof vests. It is about four times stronger (strength/weight) than the best Kevlar. A table of the strength of materials. [Look at Longitudinal Tensile Strength/ Density]







From a European Spaceward Association presentation on Dec 7, 2008: At Cambridge University, we have recently introduced a method for the spinning of pure carbon nanotube fibres directly from the gas phase of a chemical vapour deposition reactor. The major benefit of this process is the ability to continuously collect the pure and uniform nanotubes as a transparent thin-film or as a high-performance fibre. While the best strength (2.5 N/tex) and stiffness (160 N/tex) promise competition for established carbon fibres, the maximum energy absorbed at fracture (up to 100 J/g) is considerably higher. When tested in small gauge lengths, and thus less sensitive to defects arisen from instabilities in the production line, these fibres show remarkable combination of tensile strengths (5-10 N/TEX), stiffness and toughness which makes them the strongest materials ever tested. In this presentation I will show in detail how these fibres are produced and discuss how their properties can still be significantly improved without the need to apply any extra additives or post-processing. These challenges will be set against the scaling-up plan already under development.


The Times UK claims Alan Windle's team at Cambridge University has created the world’s strongest ribbon: a cylindrical strand of carbon that combines lightweight flexibility with incredible strength and has the potential to stretch vast distances.

The Cambridge team is making about 1 gram of the high-tech material per day, enough to stretch to 18 miles in length. “We have Nasa on the phone asking for 144,000 miles of the stuff, but there is a difference between what can be achieved in a lab and on an industrial level,” says Alan Windle, professor of materials science at Cambridge University, who is anxious not to let the work get ahead of itself.

The Cambridge team have found a way of combining separate nanotubes into structures that bind to form longer strands.


FURTHER READING



Also from the Luxembourg conference:
The long awaited presentation by Prof. Nicola Pugno from Politecnico di Torino, Italy, on the role of defects in the design of a space elevator cable brought clarifications on the thermo dynamical limits of designing such a super strong mega cable. According to Prof. Pugno, even applying healing processes fabricated pure CNT cables will never be without defects. Based on quantized fracture mechanics already an exceptional small defect like a single nano pin hole caused by a missing carbon atom in the hexagonal molecule of a CNT results in a strength reduction of about 20% from the theoretical value for the single nanotube! Extrapolating this to the mega cable of the space elevator, where larger nano holes and nano cracks are unavoidable the actually achievable strength is about one third of the theoretical strength. Assuming a theoretical strength of 100 GPa for a mega tether this means an actual value of 30 GPa with an upper thermo dynamical limit at 45 GPa. Following Prof. Pugno’s proposal efforts should focus on designing a system with a flaw tolerant mega cable of 10 GPa which should be practical on the multi scale. Implications for the design of the space elevator system are an increased taper ratio and mass of the tether, reducing payload capacity.


The history of carbon nanotube work at Cambridge from 2004 to 2008.

Strength of Material and Tapering of the Space Elevator

Here is the italian paper on theoretically lower maximum strength for large scale carbon nanotubes.

the taper ratio of 10 GPa g/cc goes to 613. While the taper for 30 Gpa g/cc is 7 (with 20% safety margin). So you need about 80 times more material for the elevator.

But lunar and Mars space elevators would still be reasonable and economic.

Here is a paper that discusses ribbon mass and taper ratios with different strength of material.

20 GPa g/cc is about 100 taper.( with 2 times safety margin)
20 GPa g/cc with no safety margin is 12 taper.
20 GPA g/cc with 20% safety margin is 20 taper.

Higher taper means a lot more material at the top to support the weight without breaking and then thinning out toward the bottom.

eg. A taper of 20 means 20 meters wide at the top to hold 1 meter wide at the bottom.

10 GPa g/cc [MYuri's] is better than anything else. Stronger than M5 fiber, Zylon, Spectra 2000 etc... Carbon nanotube fibers would finally be the best in practice. As the claim states the strongest ribbon ever. 10 GPa g/cc would still fall short of good enough for a practical earth space elevator. But even if theoretical maximums are reached, earth space elevators push what is possible with materials. Thus I like space piers and really good orbital skyhooks more which are very useful for lowering the cost of space access and less demanding. Plus some really nice tall towers would be possible.

Properties of diamond
Observed tensile strength up to 60 GPa observed and 90-250 GPa in theory. Density 3.5 grams/cc
17-54 MYuri but it is brittle and in other ways unsuitable for space elevators.
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