K Variations and Anisotropy: Microstructure Effect and Numerical Predictions

[+] Author and Article Information
Xu-Dong Li

School of Materials Science and Engineering, Gansu University of Technology, 85 Lan Gong Ping, Lanzhou, Gansu Province, 730050, P. R. China

J. Eng. Mater. Technol 125(1), 65-74 (Dec 31, 2002) (10 pages) doi:10.1115/1.1525252 History: Received June 05, 2002; Revised August 20, 2002; Online December 31, 2002
Copyright © 2003 by ASME
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A simulated polycrystalline aggregate consisting of 2114 arbitrarily polygon-shaped grains. Planar microcracks of different sizes are embedded in the aggregate of infinite medium. D denotes average grain size of the aggregate (D=10 microns). The dashed lines within Fig. 1 indicate microcracks of different sizes.
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Schematic illustration of broken grains (a) of varying crystallographic orientation with respect to loading direction; (b) in which reference and local crystallite co-ordinate frames are defined.
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(a) Illustration of numerical grids and refinement of boundary elements used to mesh the crack domain. Locations of centroid of elements are presented; (b) Illustration of an element shared by grains and shared area
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Duplicated local microstructure and mesoscopic stress distribution. (a) a microcrack of 2c/D=5 and broken grains; (b) spatial grain modulus ratios in grains intersected by the crack front; (c) appearance of computationally-scanned image of distribution of grain anisotropy ratio in broken grains; and (d) image of distribution of mesoscopic stress the broken grains.
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Illustration of grain geometry effect on K-Ratio evolution along a microcrack front. (a) The geometry effect imposes strong disturbances if grain shapes are treated differently rather than identically. (b) The grain geometry effect increases if the crack size is smaller.
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Demonstration, by (a) and (b), of the dependence of K Variation on local mesoscopic stress in intersected grains for a smaller crack (2c/D=5). (c) the effect of crystal anisotropy on K variations and deviations of anisotropic K away from isotropic counterparts.
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Crack size effect on K variation along the crack front (Ni material)
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Quantitative assessment of local dependence of anisotropic K for a crack of 2c/D=48. (a,d) inhomogeneous mesoscopic stress distributions due respectively to random and local preferential crystallographic orientations in grains nearby the location Q; (b,e) indications of contribution of 200 broken grains, closer to the location Q, to the anisotropic K; (c,f) local contribution per broken-grain-area in the 200 grains (the grain ID is indicated in a pair of brackets).




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