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Title: Instabilities of high speed dislocations
Author: Verschueren, Jonas
ISNI:       0000 0004 9350 7037
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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Despite numerous theoretical and computational works, a clear understanding of dislocations travelling at speeds comparable to those of the speed of sound of the material is lacking. In this thesis, a lattice dynamics model of uniformly moving dislocations is derived and used to uncover the existence of mechanical instabilities at characteristic dislocation speeds. These instabilities are shown to emanate from resonances in the atomic interactions between the dislocation and the lattice vibrations at material-dependent dislocation velocities. We then go on to explain how these resonances may be the onset for an atomistic kinematic generation mechanism, applicable to gliding edges as well as screws. The existence of these instabilities and subsequent kinematic generation mechanism are confirmed in equivalent molecular dynamics simulations of realistic metals. Since resonances are observed to be excited at dislocation speeds far below the shear wave speed of the material, kinematic generation may be more important than previously assumed in moderate and high strain rate phenomena including adiabatic shear banding and industrially relevant processes such as machining, forging and wear.
Supervisor: Dini, Daniele ; Balint, Daniel ; Sutton, Adrian Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral