HR: 1340h
AN: MR33A-0140    [Abstracts]
TI: Controls of Fluid Chemistry on Subcritical Crack Growth
AU: * Bruton, C J
EM: bruton1@llnl.gov
AF: Lawrence Livermore National Laboratory Atmospheric, Earth and Energy Dept., L-221 7000 East Ave., Livermore, CA 94550 United States
AU: Knauss, K G
EM: knauss1@llnl.gov
AF: Lawrence Livermore National Laboratory Atmospheric, Earth and Energy Dept., L-221 7000 East Ave., Livermore, CA 94550 United States
AU: Viani, B E
EM: viani1@llnl.gov
AF: Lawrence Livermore National Laboratory Atmospheric, Earth and Energy Dept., L-221 7000 East Ave., Livermore, CA 94550 United States
AU: Bonner, B P
EM: bonner1@llnl.gov
AF: Lawrence Livermore National Laboratory Atmospheric, Earth and Energy Dept., L-221 7000 East Ave., Livermore, CA 94550 United States
AB: The role of water and its dissolved content in fracturing and rock deformation (e.g. water weakening) is recognized but poorly understood. Available experimental data are very limited, and constrained largely to 25°C. Dove (1995) proposed that subcritical crack growth in quartz is controlled by its surface chemistry, by analogy with models for mineral dissolution kinetics. The role of surface chemistry in fracturing and the relation between fracturing and the breakage of bonds during mineral dissolution suggest new ways to quantify and model the impact of fluid chemistry on fracturing. We are using a hydrothermal atomic force microscope (HAFM) to image and directly measure fracture growth velocity under hydrothermal conditions at sub-micron resolution at temperatures up to 150°C with precise control of fluid chemistry. We built a specially designed sample bending apparatus (jig) to fit within the HAFM sample chamber. A Vickers indenter is used to initiate a 5 μm long crack in float glass, our initial test material. When the glass plate is positioned in the bending jig such that the induced crack is directly over the pivot point, we apply bending stress to grow the crack to about 30 μm in the HAFM while tracking fracture growth. Starting with a 5 μm crack reduces residual stress, and limiting crack growth to 30 μm ensures constancy of the stress intensity factor. We are calculating the stress intensity factor at the crack tip using the curvature of the surface and the material properties, measuring the radius of curvature in the bending jig with a vertical scanning interferometer. Propagation of previously initiated fractures will be imaged as a function of temperature, pH and fluid composition. We are now testing the device in the HAFM, with the ultimate aim of developing mechanistic models for the impact of fluid chemistry on subcritical crack growth. This work was conducted under the auspices of the U.S. Dept. of Energy by the Univ. of California, Lawrence Livermore National Laboratory (LLNL) under Contract No. W-7405-Eng-48. The project (05-ERD-035) was funded by the Laboratory Directed Research and Development Program at LLNL.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1099 General or miscellaneous
DE: 3902 Creep and deformation
DE: 3999 General or miscellaneous
DE: 5104 Fracture and flow
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005