The mechanisms governing the activation of dislocation sources in aluminum at different strain rates

Research output: Contribution to journalArticlepeer-review

Authors

Colleges, School and Institutes

External organisations

  • Imperial College London

Abstract

This article examines the time to activate Frank-Read sources in response to macroscopic strain rates ranging from 101 s-1 to 1010 s-1 in aluminium under athermal conditions. We develop analytical models of the bowing of a pinned dislocation segment as well as numerical simulations of three dimensional dislocation dynamics. We find that the strain rate has a direct influence on both the activation time and the source strength of Frank-Read sources at strain rates up to 106 s-1, and the source strength increases in almost direct proportion to the strain rate. This contributes to the increase in the yield stress of materials at these strain rates. Above 106 s-1, the speed of the bowing segments reaches values that exceed the domain of validity of the linear viscous drag law, and the drag law is modified to account for inertial effects on the motion of the dislocation. As a result the activation times of Frank-Read sources reach a finite limit at strain rates greater than 108 s-1, suggesting that Frank-Read sources are unable to operate before homogeneous nucleation relaxes elastic stresses at the higher strain rates of shock loading. Elastodynamic calculations are carried out to compare the contributions of Frank-Read sources and homogeneous nucleation of dislocations to plastic relaxation. We find that at strain rates of 5×107 s-1 homogeneous nucleation becomes the dominant generation mechanism.

Details

Original languageEnglish
Pages (from-to)273-292
Number of pages20
JournalJournal of the Mechanics and Physics of Solids
Volume84
Early online date12 Aug 2015
Publication statusPublished - 1 Nov 2015

Keywords

  • Dislocation dynamics, Frank-Read sources, Homogeneous nucleation, Source activation time, Yield point