Clarifying the definition of ‘transonic’ screw dislocations

Journal Article · Sun Feb 07 00:00:00 EST 2021 · Philosophical Magazine (2003, Print)

DOI:https://doi.org/10.1080/14786435.2021.1876269· OSTI ID:1875792

Blaschke, Daniel ^[1]; Chen, Jie ^[1]; Fensin, Saryu Jindal ^[1]; Szajewski, Benjamin A. ^[2]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Army Research Lab., Adelphi, MD (United States)

We report a number of recent Molecular Dynamics (MD) simulations have demonstrated that screw dislocations in face centred cubic (fcc) metals can achieve stable steady state motion above the lowest shear wave speed (v_shear) which is parallel to their direction of motion (often referred to as transonic motion). This is in direct contrast to classical continuum analyses which predict a divergence in the elastic energy of the host material at a crystal geometry dependent ‘critical’ velocity v_crit. Within this work, we first demonstrate through analytic analyses that the elastic energy of the host material diverges at a dislocation velocity (v_crit) which is greater than v_shear, i.e. v_crit>v_shear. We argue that it is this latter derived velocity (v_crit) which separates ‘subsonic’ and ‘supersonic’ regimes of dislocation motion in the analytic solution. In addition to our analyses, we also present a comprehensive suite of MD simulation results of steady state screw dislocation motion for a range of stresses and several cubic metals at both cryogenic and room temperatures. At room temperature, both our independent MD simulations and the earlier works find stable screw dislocation motion only below our derived v_crit. Nonetheless, in real-world polycrystalline materials v_crit cannot be interpreted as a hard limit for subsonic dislocation motion. In fact, at very low temperatures our MD simulations of Cu at 10 Kelvin confirm a recent claim in the literature that true ‘supersonic’ screw dislocations with dislocation velocities v>v_crit are possible at very low temperatures.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 1875792
• Report Number(s): LA-UR-20-25514
• Journal Information: Philosophical Magazine (2003, Print), Journal Name: Philosophical Magazine (2003, Print) Journal Issue: 8 Vol. 101; ISSN 1478-6435
• Publisher: Taylor & Francis
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
dislocations in crystals
limiting velocity
transonic motion