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One of the main mechanisms for dislocation multiplication under stress is the Frank-Read mill or Frank-Read source. The operation of a Frank-Read source can be observed on a dislocation segment pinned at its ends (movies FRsource.gif and source_film.gif)

Under stress, a dislocation segment pined at one end act as a spiral source. Similar features is also observed at the surface of solids during cristal growth (movie spiral.gif)

When a Frank-Read source interacts with other dislocations, its critical stress for dislocation multiplication is modified. Interactions between two sources illustrate this property. The critical stress for dislocation multiplication is decreased or increased when two repulsive (sources_repul.gif) or attractive (sources_atrac.gif) dislocations are respectively considered.


Annihilation of a screw dipole by cross-slip: Two dislocations of opposite sign glide in neighbouring parallel slip planes and annihilate each other by changing their slip planes (movie ys_film.gif).

Obstacle by-passing: A screw dislocation can by-pass an obstacle, here a sessile dislocation segment of same sign, by a double cross-slip process (movie dcs_film.gif).


Dislocation-Dislocation reactions:

Formation of a reaction junction between two attractive dislocations: When two dislocations gliding in non-coplanar slip planes intersect each other, the formation of a junction can be energetically favoured. The destruction of dislocation junctions under stress contributes to strain hardening in multislip. The mechanism of dislocation formation and destruction can be visualised as the zipping (tricotage.gif )and unzipping (TDT.gif) of dislocation sessile length 

Plasticity is the macroscopic outcome from the combination of many dislocation elementary properties at the micro and mesoscopic scale. This is illustrated here with the deformation of a fcc single crystal (Cu) of linear dimension 15 micrometers. The stress tensile axis is [100], the imposed strain rate is 50 per second and the plastic strain reached at the end of this sequence is 0.1 percent (movie boite_film.gif). 

Interaction of one single dislocation line with the forest: In fcc metals the yield stress and the strain hardening are governed by the forest interactions, i.e., the interactions with the dislocations intersecting the glide planes of moving dislocations (forest_film.gif).


The hardening of structural materials can be obtained by solving a boundary value problems when the plasticity is predicted by discrete dislocation simulation. Here the dislocation motions in a metal matrix composite, Al/Al2O3 reinforced by long fibres oriented along [001] (compo-DCM-45-1.mov). We observed an accumulation of dislocation along the interface matrix/fbers and also in the channel of small dimension.


A Frank Read source sends dislocations through a random set of cubic unshearable precipitates. They are by-passed according to the Orowan's model. 
    One can notice loop pile-up around each precipitates crossing the glide plane containing the source. The shape of the Orowan loops is either triangular or hexagonal corresponding to the intersection between a (100) cube and a (111) plane.  

When many loops are present, passages between precipitates are narrower. Consequently the passage of dislocations is more difficult and the rythm of the source is slowed down (precipitate.gif).
Random sources are introduced in a closed grain (lower dodecahedron). 
A tensile applied stress is applied along the vertical axis. Sources are then activated and a pile up is observed on the grain boundary. When the stress at the head dislocation in the pile up is high enough, a dislocation crosses the grain boundary and enters the upper grain. Such a situation naturally leads to the Hall-Petch relationship between the grain size and the yield stress (bicrystal.gif).  

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