A promising new high-tech material—carbon nanotubes

Description of carbon nanotubes:

Do you want to wear a bulletproof vest woven with nano-spun threads and feel the excitement of being "invulnerable"? Do you want to own a cup made of nano-ceramics and experience the joy of being "unbreakable"? It won't be long before magical nanotechnology can make your wishes come true.

Nanotechnology is a new science and technology that studies the characteristics and interaction rules of substances (including atoms and molecules) at the nanometer scale. It is a comprehensive science and technology that has developed rapidly since the 1980s. Like centimeters and micrometers, nanometers are a scale unit, with one nanometer being one billionth of a meter. Assume that the diameter of a hair is 0.05 mm, then the hair is cut into 50,000 pieces on average according to the diameter, and the thickness of each piece is 1 nanometer.

carbon nanotube 

Carbon nanotubes are an important new member in the "nanoworld." It belongs to the carbon crystal family like diamond and graphite. It is a carbon tube made of rolled layers of carbon atoms (carbon nanotubes made of rolled single-layer carbon atoms are called single-walled carbon nanotubes, and multi-layered carbon nanotubes are called single-walled carbon nanotubes. The tubes are called multi-walled carbon nanotubes). The diameter of the tube is only a few nanometers, the length is only a few thousand nanometers (i.e., a few microns), and the thickness of the tube wall is only a few nanometers. It is like a hollow cylindrical "cage tube" rolled into a wire mesh. They are so tiny that tens of thousands of them side by side would only be as wide as a human hair. They are actually fibers with a very high length-to-diameter ratio.

Carbon nanotubes have aroused widespread interest since their discovery in 1991, especially the discovery of single-walled carbon nanotubes and their successful synthesis in macroscopic quantities. Since then, scientists from many countries have devoted a lot of energy to conducting a series of studies on the preparation, properties, and applications of carbon nanotubes. Carbon nanotubes have properties similar to fullerene molecules (there are five-membered carbon rings on their end faces). Because of its unique electronic structure and physical and chemical properties, the study of carbon nanotubes has excellent theoretical significance and potential application value. It has become one of the most cutting-edge research fields in physics, chemistry and materials science.

carbon nanotube 

The scientists calculated how carbon nanotubes and their fibers experience fatigue

How strain and stress affected the "perfect" nanotubes and those assembled into fibers, found that while the fibers would fail over time under cyclic loads, the nanotubes themselves might remain perfect. How long a pipe or its fibers last in a mechanical environment determines its usefulness.

That makes the study, published in the journal Science Advances, important to Rice materials theorist Boris Yakobson, graduate student Nitant Gupta, and Evgeni Penev, assistant research professor at rice's George R. Brown School of Engineering. They quantified the effect of cyclic stress on nanotubes using state-of-the-art simulation techniques, such as the kinetic Monte Carlo method. They hope to provide researchers and industry with a way to predict the expected service life of nanotube fibers or other components under given conditions.

carbon nanotube 

"The time dependence of the strength or endurance of individual nanotubes has long been investigated in our group, and now we are considering the effects on the cyclic loading of nanotubes and their fibers or components," Penev said."Recently, several experiments have reported that carbon nanotubes and graphene can fail catastrophically due to fatigue, but without progressive damage. That curiosity and surprise were enough to rekindle our interest and ultimately lead us to the work."

Perfect carbon nanotubes are considered to be among the strongest structures in nature, and they tend to remain intact unless some violent impact takes advantage of their brittleness and shatters them to pieces. Using atomic-scale simulations, the researchers found that under environmental conditions, and even when bent or bent, the nanotubes were able to handle everyday pressures well. When the stone-Wales defect does occur spontaneously, the effect on these "tireless" nanotubes is negligible.

carbon nanotube 

They found that the same principle applies to defect-free graphene.

But when millions of nanotubes are bundled into linear fibers or other structures, the van der Waals forces that bind parallel nanotubes together do not stop them from slipping. Earlier this year, researchers have demonstrated how friction between nanotubes leads to stronger interfaces between nanotubes and is responsible for their incredible strength. Using this model, they have now tested how fatigue develops under cyclic loads and how fatigue ultimately leads to failure.

Whenever the nanotube fiber is stretched or stretched, it essentially returns to its original form once the tension is released."Most" is the key; The amount of residual slip is small and increases with the increase of cycle number. This is plasticity: deformation with irreversible incomplete recovery.

"Cyclic loading of the nanotube fibers causes adjacent nanotubes to either slip away or come close to each other, depending on which part of the cycle they are in," Gupta explained."This slip is not equal, resulting in the accumulation of total strain per cycle. This is called the strain ratchet because the total strain always increases in one direction, just as the ratchet moves in one direction."


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