HR: 0800h
AN: T11A-0342    [Abstracts]
TI: Crack Coalescence in Molded Gypsum and Carrara Marble
AU: * Wong, N
EM: lnywong@hotmail.com
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave, Rm 1-339, Cambridge, MA 02139, United States
AU: Einstein, H H
EM: einstein@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave, Rm 1-339, Cambridge, MA 02139, United States
AB: This research investigates the fracturing and coalescence behavior in prismatic laboratory-molded gypsum and Carrara marble specimens, which consist of either one or two pre-existing open flaws, under uniaxial compression. The tests are monitored by a high speed video system with a frame rate up to 24,000 frames/second. It allows one to precisely observe the cracking mechanisms, in particular if shear or tensile fracturing takes place. Seven crack types and nine crack coalescence categories are identified. The flaw inclination angle, the ligament length and the bridging angle between two flaws have different extents of influence on the coalescence patterns. For coplanar flaws, as the flaw inclination angle increases, there is a general trend of variation from shear coalescence to tensile coalescence. For stepped flaws, as the bridging angle changes from negative to small positive, and further up to large positive values, the coalescence generally progresses from categories of no coalescence, indirect coalescence to direct coalescence. For direct coalescence, it generally progresses from shear, mixed shear-tensile to tensile as the bridging angle increases. Some differences in fracturing and coalescence processes are observed in gypsum and marble, particularly the crack initiation in marble is preceded by the development of macroscopic white patches, but not in gypsum. Scanning Electron Microprobe (SEM) study reveals that the white patches consist of zones of microcracks (process zones).
DE: 8010 Fractures and faults
DE: 8094 Instruments and techniques
DE: 8199 General or miscellaneous
SC: Tectonophysics [T]
MN: 2007 Fall Meeting