College Park, Maryland June 6 - 10 , 2004 |
T3-C6 (5:15 PM): Quantitative Texture Analysis of Experimentally Deformed Fine-grained D2O ice by Neutron Diffraction
S.M. McDaniel (Los Alamos National Laboratory; University of Washington), K.A. Bennett (Office Of Basic Energy Sciences/DOE), W.B. Durham (Lawrence Livermore National Laboratory), E.D. Waddington (University of Washington), V. Luzin (NIST Center for Neutron Research)
Quantitative textures measurements of fine-grain D20 ice experimentally deformed polycrystalline D20 ice cylinders were performed by neutron diffraction on BT-8 at the NIST Neutron Research Reactor. The aim was to determine the primary mechanism of ice deformation, grain-size sensitive (GSS) creep or dislocation creep. Textures in three samples (2 samples approximately 1 inch diameter X 1 inch long, 1 sample a 8mm sphere, grain size 10-100 microns) of deuterated hexagonal ice were measured by neutron diffraction using 4 principal diffraction peaks (100), (002), (101) and (102), with lambda= 1.878 angstrom, and a He-3 displex closed-cycle cryostat in conjunction with a four-circle gonimeter. Experimental pole figures were collected using the so-called hexagonal grid with angular resolution of less than 5 degrees. The Orientation Distribution Functions for each sample were calculated using POPLA and BEARTEX texture packages.
Comparison of experimental pole figures to recalculated figures show good experimental accuracy. Samples were deformed at T=222K, 224K, and 226 K, and to 30%, 22.5% and 30% strain, respectively. All samples show typical fiber texture common to hexagonal ice, with (001) parallel to the sample axes, and the axes of compression. Texture analyses reveal a similar pole distribution in all samples, with twice as many (001) poles parallel to the compression axis than to the perpendicular axis. Under the deformation conditions, grain-size sensitive (GSS) creep was expected to dominate, resulting in no texture development. However, the neutron data results indicate significant texture and grain growth, suggesting that deformation may be dominated by dislocation creep over GSS and temperature conditions, even at very low temperatures, for fine-grained ice.
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