Void formation during non-basal glide in ice single crystals under tension

Abstract

Experiments in tensile deformation of ice single crystals were carried out with rectangular specimens crystallographically oriented so that only non-basal glide on planes could occur. In the process of deformation, it was found that many small voids formed in rows parallel to the direction. These voids were thin, circular or hexagonal plates distributed in layers lying on the basal plane. The number and size of these voids increased with increasing strain, and some of them formed large cavities which finally fractured the specimens. When specimens were strain aged, the number of voids decreased while the volume of remaining voids increased. A dislocation climb model was proposed to interpret the void formation. Theoretical calculations were made for the volume of the voids with the assumption that they were formed as aggregates of vacancies left behind climbing edge dislocations lying on the planes. The results of the calculations agree quite well with the observed volumes if the edge dislocation density is taken as 10⁴ cm⁻² and the diffusion coefficient for ³H₂ or ¹⁸O is adopted for the vacancies. The orientation dependence of the volume was explained as well as its time and temperature dependence. The fact that voids are not formed by compression tests is additional support for the dislocation climb model.