Increasing contribution of grain boundary compliance to polycrystalline ice elasticity as temperature increases

• Published in: Journal of Glaciology
• Main Author: COLIN M. SAYERS
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2018
• Subjects: glacier geophysics; ice physics; ice temperature; Environmental sciences; GE1-350; Meteorology. Climatology; QC851-999; Journal of Glaciology
• Online Access: https://doi.org/10.1017/jog.2018.56; https://doaj.org/article/e5e556b2eb8a4e40a42366fba5b21028

Measured elastic stiffnesses of ice polycrystals decrease with increasing temperature due to a decrease in grain boundary stiffness with increasing temperature. In this paper, we represent grain boundaries as imperfectly bonded interfaces, across which traction is continuous, but displacement may be discontinuous. We express the additional compliance due to grain boundaries in terms of a second-rank and a fourth-rank tensor, which quantify the effect on elastic wave velocities of the orientation distribution as well as the normal and shear compliances of the grain boundaries. Measurement of the elastic stiffnesses allows determination of the components of these tensors. Application of the method to resonant ultrasound spectroscopy measurements made on ice polycrystals enables determination of the ratio BN/BS of the normal to shear compliance of the grain boundaries, which are found to be more compliant in shear than in compression. The ratio BN/BS is small at low temperatures, but increases as temperature increases, implying that the normal compliance increases relative to the shear compliance as temperature increases.