Graphene is Strong But Can It Be Durable and Tough?

By: | March 3rd, 2016

Scientists have been running tests on polycrystalline graphene for a number of years, and they have stated that it is not very resistant to cracks and fractures. This is the first theory that explains the toughness of polycrystalline graphene in detail, which is constructed by the deposition of chemical vapors. Although it is structurally quite strong, its toughness level and resistance to cracks are quite low.

Graphene consists of a single layer of carbon atoms and it is said to be one of the strongest materials. It is 200 times stronger and more structurally sound than steel, in addition to being lighter than paper. It’s electronic and industrial properties and applications are endless. But scientists are still running tests on its durability and strength, to ensure that it can live up to the hype and expectations of the scientific community.

Scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory have compiled the first theory about polycrystalline graphene and its toughness. Although it is not as strong as pristine monocrystalline graphene, it is stronger than other materials that are known to mankind. However, its low toughness has somewhat mellowed the excitement over its impressive properties of strength.

Berkeley Lab scientist, Robert Ritchie, explained in a statement, “This material certainly has very high strength, but it has particularly low toughness–lower than diamond and a little higher than pure graphite. Its extremely high strength is very impressive, but we can’t necessarily utilize that strength unless it has resistance to fracture.”

As a leading scientist in the study and an expert on the subject of why materials fail, he has compiled this study with Shivni Shekhawat, a Miller Research Fellow in his group. They were successful in formulating a statistical model for testing the toughness of polycrystalline graphene to find out the property that is lowering its toughness level.

Richie further explained in a statement, “It’s a mathematical model that takes into account the nanostructure of the material. We find that the strength varies with the grain size up to a certain extent, but most importantly this is a model that defines graphene’s fracture resistance.” He further explained that every structural material must have high toughness variability and a property to resist deformation.

Mostly, in critical structures, toughness takes precedence over strength, because when you look at structures, such as a nuclear reactor pressure container, it is manufactured from low-strength steel, not ultra-high strength steel. This is due to the fact they are used for their ability to resist any catastrophic fracture in the structure. The authors have further deduced that graphene can be used in manufacturing leading-edge applications for the electronic industry and biological devices, which require corrosion-resistant coatings and materials, but for structural reliability, graphene requires extensive structural changes at the atomic level.

Ritchie deduced that the key to doing this is to change the vapor composition through which graphene is formed. He stated, “Our numbers were consistent with that one experimental number. In practical terms, these results mean that a soccer ball can be placed on a single sheet of monocrystalline graphene without breaking it. What object can be supported by a corresponding sheet of polycrystalline graphene? It turns out that a soccer ball is much too heavy, and polycrystalline graphene can support only a ping pong ball. Still remarkable for a one-atom-thick material, but not quite as breathtaking anymore.”

Shekhawat and Ritchie are further studying the effects of hydrogen atoms on the durability and toughness of the material, but presently they are still observing cracks in the structure. They will continue the studies to find an atomic substance that will enhance the toughness variability of graphene.

Paul Cook

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