Supersonic Dislocations

Science  12 Feb 1999:
Vol. 283, Issue 5404, pp. 901e
DOI: 10.1126/science.283.5404.901e

When a material is deformed, dislocations form and move through it. Under normal deformation conditions, dislocation motion is determined by thermally activated processes and remains relatively slow, but under high strain they can speed up significantly. According to elasticity theory, the speed at which they can move is limited by a characteristic sound barrier of the material. Theory also predicts a single supersonic state, but it has been unclear whether the sound barrier can be overcome to reach it. Gumbsch and Gao (p. 965) have performed molecular dynamics simulations of a moving edge dislocation in a crystalline solid. They show that if the dislocation is created while the material is under high-strain conditions, then the dislocation moves at high speed right after nucleation, overcoming the sound barrier. The dislocations can move at a range of velocities above the sound barrier rather than at a single supersonic velocity and require energy to be drawn from the applied strain field.

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