Dislocation Mechanisms of Plastic Deformation of Ice

Characters and properties of dislocations in ice are thoroughly reviewed on the basis of the knowledge hitherto obtained by the X-ray topographic method as well as recently found dynamical behavior. Extremely low energy of the faults on the basal plane found by the method leads us to conclude that all of the dislocations in ice should be extended as wide as several tens to one hundred nano-meter, depending upon their Burgers vectors, on the basal plane. The motion of dislocations, therefore, is severely restricted on the basal plane. The strong anisotropy of plastic deformation of ice single crystal is interpreted in terms of this restriction; i.e., the primary slip caused by glide motion of the (1/3)<1120> dislocations on (0001) is a unique easy slip system in ice because glide planes of the other dislocations do not coincide with their extended plane or the basal plane. It is also shown that the secondary slip system <1120>/{1010} is due to glide motion of the constricted (1/3)<1120> dislocations on the-prismatic planes {lOTO). Since only very short segments can glide on {1010) owing 'to the tendency of the dislocations to lie on (0001), this slip system is far less easier than the primary one in spite of larger velocities of the segments than the basal Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987124