Probing the character of ultra-fast dislocations

Area of Science:

• Materials Science
• Condensed Matter Physics
• Mechanics of Materials

Background:

• Plasticity is governed by dislocation motion, historically measured under low stress and strain rate conditions.
• Data on dislocation velocity at high stress conditions are scarce and often rely on indirect measurements.
• Existing methods are limited by dislocation density effects, hindering direct velocity assessment.

Purpose of the Study:

• To develop and validate a new experimental approach for directly measuring dislocation velocities under extreme stress conditions.
• To provide atomistic simulation-based predictions for guiding experimental design and interpretation.
• To explore phenomena occurring at extreme strain rates and stresses.

Main Methods:

• Atomistic simulations of tantalum to predict dislocation behavior under extreme conditions.
• Proposed experimental technique involving nanoindentation to create dislocation loops.
• Shockwave loading to drive dislocations and electron microscopy for measuring displacement and calculating velocity.

Main Results:

• Atomistic simulations provide detailed predictions of dislocation flow in tantalum.
• The proposed three-step method (nanoindentation, shockwave, electron microscopy) is predicted to be feasible.
• Simulations reveal potential for observing unique phenomena like transonic dislocations and loop stretching.

Conclusions:

• The developed simulation framework enables direct measurement of average dislocation velocity at very high applied shear stress.
• This approach opens new avenues for understanding material plasticity under extreme dynamic loading.
• The findings pave the way for novel experiments probing fundamental dislocation dynamics.