Supersonic Screw Dislocations Gliding at the Shear Wave Speed.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid Mechanics

Background:

• Dislocation motion is key to metal deformation, strength, and ductility.
• Screw dislocations are critical for plastic flow, but their maximum speed and stress dependence are debated.

Purpose of the Study:

• To investigate the speed limit of screw dislocations.
• To determine the stress dependence of screw dislocation motion.
• To challenge existing theories on dislocation dynamics.

Main Methods:

• Large-scale molecular dynamics simulations were employed.
• The behavior of full screw dislocations and twinning partial screw-type dislocations was analyzed.

Main Results:

• Full screw dislocations and twinning partial screw-type dislocations can achieve steady glide at shear wave velocity.
• Supersonic motion of these dislocations is possible, contradicting theories with energy dissipation singularities.
• Dislocation motion is influenced by shear stress components not included in the resolved shear stress (RSS).

Conclusions:

• Screw dislocations can move supersonically, exceeding previously accepted limits.
• Conventional Schmid's law is insufficient to describe screw dislocation motion.
• New theoretical frameworks are needed to account for observed supersonic dislocation speeds and complex stress dependencies.