Strain-Induced Fabric Development in Ice under Hydrostatic Pressure

通过改进对冰变形过程中晶界迁移过程的理解，为pi理解和模拟以下现象提供了支持：有利取向晶粒深度处广泛变形的存在和组织的支配；2 .滑移晶粒在剪切方向上的生长，以及这是邻近晶粒相对取向的函数还是滑移晶粒的基本特征；压力对织物深度发育过程的速率和/或平衡的影响。他们的工作假设是，滑移晶粒可以在不需要再结晶的情况下扩展，并且这一过程与变形过程中晶界迁移率的各向异性密切相关。为了寻找这些机制的证据，他们提出了以下一系列对颗粒状淡水冰的实验室观察：在低偏应力和一定压力、温度范围内进行密闭压缩实验，形成优选的c轴取向，并引起生长。使用标准技术记录在不同温度和剪切应力水平下变形显微组织的c轴方向、晶粒尺寸和形状。3 .利用电子背散射图（EBSP）分析记录变形材料中滑移和相邻晶粒的a轴和c轴方向。利用表面刻蚀来识别变形晶粒中的滑移线阵列，并将这些观测结果与EBSP结果中观察到的晶界结构相结合。从这项研究中得到的基本认识预计将促进对冰芯解释的古气候的更好理解，以及对冰川和冰盖力学模型的改进。

Support is provided to allow the PIs to understand and model, through an improved understanding of grain boundary migration processes in deforming ice, the following phenomena:1. The survival of extensive deformation and domination of the microstructure at depth of favorably-oriented grains, 2. The growth of slipping grains in the direction of shear, and whether this is a function of the relative orientations of neighboring grains or a fundamental characteristic of slipping grains, and3. The effects of pressure on the rate and/or balance of the processes responsible for fabric development at depth.Their working hypothesis is that slipping grains can propagate without requiring recrystallization, and that this process is closely associated with anisotropy in grain boundary mobility during deformation. To seek evidence of these mechanisms, they propose the following series of laboratory observations on granular freshwater ice:1. Conduct confined compression experiments at low deviatoric stresses and a range of pressure and temperature to develop a preferred c-axis orientation and cause growth.2. Use standard techniques to document c-axis orientations, grain size and shape of the deformed microstructures for several temperatures and shear stress levels.3. Employ electron backscatter pattern (EBSP) analysis to document a- and c-axis orientations of slipping and abutting grains in the deformed material.4. Use surface etching to identify slip line arrays in the deforming grains, and couple these observations with the grain boundary structures observed in the EBSP results.The fundamental understanding derived from this study is anticipated to foster improved understanding of paleoclimate as derived from the interpretation of ice cores, as well as improved models of glacier and ice sheet mechanics.