Slide 1
MeVArc Summary: DislocationsNick Shipman - Wednesday, 03 August
2011
1
Marc Fivel 3D Discrete Dislocation Dynamics SimulationsTEM video
showing a Frank Read Source in actionPersistent Slip Band formation
Model/Simulation/Experimental Evidence
Aarne Pohjonen Dislocation mechanisms on a near surface
voidSteve Fitzgerald Dislocations
Model for protrusion formation under E field supported by
simulationsDetails of the experimental evidence for the required
voidsMay explain conditioning and BD resistance ranking by crystal
structure{
TRDIS simulation of Frank Read sourceTaken using
Transverse-Electron-MicroscopyA Frank-Read Source is a mechanism
explaining the generation of multiple dislocations in specific well
spaced slip planes in crystals when they are deformed. Wikipedia1.
TEM video showing a Frank-Read source in action2
2. Persistent Slip Band Formation
The diagrams on the right show a way in which slip bands can be
formed by a dislocation moving sideways across and interacting with
other dislocations.
A schematic view of persistent slip bands and a composite TEM
image in which the channels are clearly visible.
2. Persistent Slip Band Formation~10umOne frame from the new
nodal 3D discrete dislocation simulation code Numodis which was
used to simulate low strain fatigue in AISI 316L Steel.An SEM image
courtesy of Markus Aicheler showing the damage due to pulse surface
heating on copper.3. Model for protrusion formation under
externally applied E field The concept is as follows:-Protrusions
can be created by prismatic loops which are drawn to the surface
due to an externally applied E filed.But how are the prismatic
loops formed?By the interaction of dislocations with near surface
voids.
DefinitionsPrismatic loop platelet of extra atoms
Void3. Model for protrusion formation under externally applied E
field
4. Details of experimental evidence of required voids5. Things
this theory can help explain
Possible reason for conditioning: voids are used up
Possible reason for rank by crystal structure: dislocations
travel at different speeds in different structures
Steel has highest breakdown resistance: full of C which
significantly impedes dislocation motion