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Study: Graphene Is Strong, Not Tough

Monday, February 15, 2016

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While the various properties inherent to graphene make it ideal for applications from corrosion-resistant coatings to biological devices, all uses rely on the structural reliability it is known for.

However, scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory report that while the material is strong, it is not very resistant to fracture.

The team published its findings, “Toughness and strength of nanocrystalline graphene,” in the journal Nature Communications.

Toughness: ‘Lower than Diamond’

In terms of strength, defined as a material’s resistance to deformation, the material has been billed as 200 times stronger than steel.

Berkeley Lab

Polycrystalline graphene contains inherent nanoscale line and point defects that lead to significant statistical variances in toughness and strength, according to Berkeley Lab.

The researchers say they have developed “the first known statistical theory for the toughness of polycrystalline graphene,” made with chemical vapor deposition, and found its toughness is quite low.

"This material certainly has very high strength, but it has particularly low toughness—lower than diamond and a little higher than pure graphite," Berkeley Lab scientist Robert Ritchie said in a research announcement.

"Its extremely high strength is very impressive, but we can't necessarily utilize that strength unless it has resistance to fracture."

A Mathematical Model

Ritchie and his co-author Ashivni Shekhawat developed the model to better understand and predict failure in the material.

"It's a mathematical model that takes into account the nanostructure of the material," Ritchie said. "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."

graphene atoms

Alexander AIUS / Wikimedia Commons

Graphene is a layer of carbon atoms invisible to the human eye.

Toughness and strength are often mutually incompatible properties, the scientists note.

Applications Depend on Toughness

"A structural material has to have toughness," Ritchie explained. "We simply don't use strong materials in critical structures—we try to use tough materials.

“When you look at such a structure, like a nuclear reactor pressure vessel, it's made of a relatively low-strength steel, not an ultrahigh-strength steel. The hardest steels are used to make tools like a hammer head, but you'd never use them to manufacture a critical structure because of the fear of catastrophic fracture."

Achim Hering / Wikimedia Commons

Over the past few years, graphene has been studied in a variety of applications, including corrosion-resistant coatings.

Over the past few years, graphene has been studied in a variety of applications, including corrosion-resistant coatings, flexible electronic displays and biological devices.

These uses depend on its mechanical properties for structural reliability, Berkeley Lab reports.

The team is now trying to understand more about the fracture of graphene, specifically the effects of adding hydrogen to the material. Preliminarily, they report that they are finding cracks grow more readily in the presence of the element.


Tagged categories: Asia Pacific; Coating Materials; Coatings Technology; Corrosion resistance; EMEA (Europe, Middle East and Africa); Latin America; Lawrence Berkeley National Laboratory; North America; Performance testing; Protective Coatings; Research

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