1 Twin boundary migration

This movie is comparable to the experiment shown in fig. 3 of Urai (1987). Wet carnallite, deformed at 100 degrees C and 5x10^-5 s^-1 strain rate usually develops a set of twins at the onset of deformation. These twins replace the ones which developed during sample preparation and are un-twinned by the new stress directions. Twinning is accompanied by dislocation creep. Note that the twins do not propagate into areas of undulose extinction. In the left side of the sample there is a small hard halite inclusion. After about 10% strain the twin boundaries become mobile and twin boundary migration is the main process of recrystallization at this stage.

After considerable shortening and recrystallization, strain is localized into a network of semibrittle shear zones, originating at the small halite grain mentioned above. Carnallite in these zones is recrystallized into a very fine grained aggregate, and movement along the shearzones is accompanied by ductile deformation of the moving fragments.

I would like to thank G. Spanjersberg of the Hochschuldidaktische Dienst, RWTH Aachen for digitizing the cine films.

I wish to thank Win Means for many wonderful discussions, for guidance, friendship, and fun over the past twenty or so years.