Columbia researchers find graphene can't cope with stress
Researchers at Columbia discovered that isotropic stress can cause graphene sheets to morph into a weaker, less stable structure that makes is more susceptible to mechanical failures.
Graphene, a one-atom-thick layer of carbon, is considered the strongest material known to mankind. It has found countless applications in the field of nanotechnology, including the manufacturing of stronger-than-steel-by-a-hundredfold nanotubes. However, Assistant Professor Chris Marianetti at Columbia University has exposed a fundamental structural weakness of graphene that leads to its possible mechanical failure under strain, and could change the way we use this and other materials to build nanotech devices.
Using quantum theory and aided by supercomputers, Marianetti has discovered that when pure graphene is subject to equal strain in all directions, it morphs into a new structure that is mechanically unstable – the honeycomb arrangement of carbon atoms in the graphene sheet transforms into a series of isolated hexagonal rings that is structurally weaker, causing a mechanical failure of the material.
At any temperature above absolute zero, all the atoms in a crystal vibrate with a certain intensity – the higher the temperature, the stronger the vibrations. The team led by Marianetti found that under isotropic stress, a phonon (the collective vibrational mode of atoms within a crystal) is altered and becomes "soft." The system then distorts its atoms along the vibrational mode and transitions to a new arrangement that is structurally weaker.
This is the first time a soft optical phonon has been linked to mechanical failure, and opens the way to further research that should ascertain whether, as the team suspects, this failure mechanism is present in other very thin materials as well. Strains may even be a means to engineer the properties of graphene, so understanding its limits is critical.
The Columbia research was funded by the National Science Foundation. A paper detailing the research is due to be published soon in the journal Physical Review Letters.
About the Author
Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion.
All articles by Dario Borghino
Maybe contravibrate to keep phonons out of soft spots? I don´t know anything of vibrating atoms, but if it´s anything like how harmonics work, I´ll bet its possible to introduce energy to keep graphene phonons from reaching the state described in the article above.
This is the kind of problem that makes materials scientists eager to get to work in the morning. Are there ways to compensate for the weakness of graphene? Would alternating layers of some other planar material do the trick? Should be fun to see the solutions that researchers come up with.
\"when pure graphene is subject to equal strain in all directions\"?
Then don\'t make a spherical balloon out of a sheet of it.
(I wasn\'t planning to.)
It\'s hard to think of other cases that these calculations apply to.
If similar results show up for the very anisotropic stress and strain on nanotubes, I will start to worry.
The inter atomic forces are much greater than the current Ultimate Tensile strength of materials. The goal of materials science is to get as close to the atomic strength as possible.
We have made much progress but we are a long way from meeting the goals we have set.
This is only calculated failure? What does real world testing tell us?
All I can say is that I spent good money on a graphite fiber fishing pole and on the first cast, it snapped into two pieces.
Not a spherical balloon. A spherical chicken.
Sounds to me like engineering around this type of failure is going to require an immense amount of computing power to prevent random occurrences of collective vibrations.
I agree with bas on the harmonics point of view and see some kind of noise cancelling/energy input techniques as useful strategies for overcoming this problem.
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