HR: 1330h
AN: V12A-0552    [PDF]
TI: Microstructural Analysis of Welding: Deformation and Strain
AU: * Quane, S L
EM: squane@eos.ubc.ca
AF: Igneous Petrology Lab, University of British Columbia, 6339 Stores Rd., Vancouver, BC V6T 1Z4 Canada
AU: Russell, K
EM: krussell@eos.ubc.ca
AF: Igneous Petrology Lab, University of British Columbia, 6339 Stores Rd., Vancouver, BC V6T 1Z4 Canada
AB: Welding in pyroclastic deposits involves the sintering, compaction and flattening of hot glassy particles and is attended by systematic changes in physical properties. Welded materials contain implicit information regarding the total accumulated strain as well as the mechanisms of deformation. Here, we use detailed microstructural analysis of synthetic and natural welded materials to make quantitative estimates of strain and constrain the rheology of these materials during the welding process. Part one of our study comprises microstructural analysis of end products from unconfined high temperature deformation experiments on sintered cores of soda-lime silica glass spheres. This analogue material has relatively simple and well-characterized starting properties. Furthermore, the initially spherical shapes of particles provide excellent strain markers. Experiments were run at a variety of temperatures, strain rates and stresses resulting in end products with varying degrees of total strain. The nature of strain partitioning and accumulation are evaluated using image analysis techniques on scanned images and photomicrographs of thin sections cut perpendicular to the loading direction of each experimental product. Shapes of the individual deformed particles (e.g., oblate spheroids) were determined and the Scion image analysis program was used to create a best-fit ellipse for each particle. Statistics collected on each particle include: axial dimension (a), vertical dimension (c) and angle from the horizontal. The data are used to calculate the oblateness of each particle (1-c/a) and the angle of deformation induced foliation. Furthermore, the relative proportions of visible blue epoxy in the sample scans determine bulk porosity. The average oblateness of the particles is a direct, independent measure of the accumulated strain in each sample. Results indicate that these measured values are equal to calculated theoretical values of oblateness for spheroids undergoing the amount of constant-volume strain as determined by machine displacement. This information, combined with the near horizontal foliation angle for all samples strongly suggests that, in these experiments, all deformation is coaxial. Total strain in these experiments is accommodated by both longitudinal strain (calculated from porosity loss) and axial strain ("bulging" of the sample). A goal of ongoing analysis is to determine the role and proportion of each type of strain with increasing deformation. Furthermore, we are micro-analyzing products from experiments performed on natural pyroclastic materials for comparison with our dataset of results from similar analyses of naturally occurring samples.
DE: 8404 Ash deposits
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting