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The strength of a material is a measure of its ability to withstand a load without breaking. Scientists in search of the strongest materials have recently turned their attention to nanomaterials, which have few of the defects that typically reduce a material's strength. On page 300 of this issue, Banerjee et al. (1) show that when nanoscale single-crystal diamond needles are elastically deformed, they fail at a maximum local tensile stress of ∼89 to 98 GPa, which is very close to the theoretical limit for this material.

The maximum possible strength that a material can have in either tension or shear is controlled by the fracture of the interatomic bonds and is on the order of 10% of the elastic or shear moduli, respectively. However, it is difficult to achieve these strengths in practice because defects in the solid will lead to inelastic relaxation or brittle fracture well before the atomic bond can be stretched to the theoretical limit. Maximum elastic tensile strains supported by bulk solids are between 0.2 and 0.4%, whereas tensile strains of up to 4% have been measured in micrometer-size whiskers (2). Recent progress in nanomaterial synthesis and nanomechanical testing has opened the possibility of probing the strength of material systems that are practically free of defects (3). In parallel, atomistic simulations based on density-functional theory and molecular dynamics can predict accurately the fracture strength of perfect crystals and allow the influence of defects and free surfaces on this property to be explored.

But is diamond really the strongest material in the universe? To read more, click here.

Category: Science