HR: 15:10h
AN: T42D-07    [PDF]
TI: Nanoindentation Creep of Quartz, Olivine, and Calcite, with Implications for Rate and State Friction Laws
AU: * Goldsby, D L
EM: David_Goldsby@brown.edu
AF: Department of Geological Sciences, Brown University, 324 Brook Street, Providence, RI 02912 United States
AU: Rar, A
EM: 2ut@email.cind.ornl.gov
AF: Department of Materials Science, University of Tennessee, and Metals and Ceramics Division, Oak Ridge National Laboratory, 434 Dougherty Engineering Building, Knoxville, TN 37996-2200 United States
AU: Pharr, G M
EM: pharr@utk.edu
AF: Department of Materials Science, University of Tennessee, and Metals and Ceramics Division, Oak Ridge National Laboratory, 434 Dougherty Engineering Building, Knoxville, TN 37996-2200 United States
AU: Tullis, T E
EM: Terry_Tullis@brown.edu
AF: Department of Geological Sciences, Brown University, 324 Brook Street, Providence, RI 02912 United States
AB: A hallmark observation from friction experiments on rocks is that the coefficient of friction increases linearly with the log of time of quasi-stationary contact. This increase in friction, or {\it state} in the rate- and state-variable friction laws, is usually attributed to an increase in real area of contact between rough surfaces caused by deformation of highly stressed contacts. This behavior is typically explored in slide-hold-slide (SHS) friction experiments at ambient temperature. Despite the importance of the evolution of the state variable for determining conditions for which earthquakes may nucleate, contact-scale deformation mechanisms in rocks remain unknown. In an effort to identify these deformation mechanisms, nanoindentation creep experiments were conducted on single crystals of quartz, olivine and calcite at room temperature and constant loads of 50 to 250 mN. The amount of creep in a typical nanoindentation creep test is indicated by the increase in indentation area with time, determined from the measured displacement of indenter into the specimen and the well-characterized geometry of the indenter tip. A major limitation of such tests, that displacements are difficult to discern from thermal noise, was eliminated by employing {\it continuous stiffness} techniques. A 45-Hz oscillation in displacement of 2 nm amplitude was imposed on a diamond Berkovich indenter held at otherwise constant load for times comparable to those in SHS tests, up to 5$\times$10$^{4}$ s. By analyzing the resulting specimen response with a frequency-specific analyzer, a nearly continuous measure of the contact stiffness, proportional to contact area, was obtained. Thus, contact area is determined over times too short for significant thermal drift. Changes in area with time from indentation tests were compared with those inferred from complementary SHS tests on quartz, olivine and calcite rocks conducted in a high pressure rotary-shear apparatus. The contact area between indenter and specimen increased linearly with log time for each mineral, in qualitative agreement with the linear increase in area with log time inferred from SHS tests. However, the rate of fractional area increase from nanoindentation tests is much larger than inferred from SHS tests, by factors of ~2, 5, and 10 for quartz, olivine, and calcite, respectively. This discrepancy may indicate that contact stresses in the two tests are the same, but that area formed during the hold in SHS tests is partially destroyed during reloading after the holds, as demonstrated for acrylic plastic and glass ({\it Dieterich and Kilgore}, 1994). Alternatively, the difference may indicate that contact stresses in rock friction experiments are significantly less than determined from indentation tests.
DE: 3902 Creep and deformation
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 5104 Fracture and flow
DE: 5120 Plasticity, diffusion, and creep
SC: Tectonophysics [T]
MN: 2003 Fall Meeting