HR: 1330h
AN: T42A-0283    [PDF]
TI: Anomalous Thermal Relaxation Induced by the Granular Composition of Berea Sandstone
AU: * Ulrich, T
EM: tju@unr.edu
AF: University of Nevada, Reno, Dept. of Physics M.S. 220, Reno, NV 89557 United States
AU: McCall, K R
EM: mccall@unr.edu
AF: University of Nevada, Reno, Dept. of Physics M.S. 220, Reno, NV 89557 United States
AU: Guyer, R
EM: guyer@physics.umass.edu
AF: University of Massachusetts, Amherst, Dept. of Physics, Amherst, MA 01003 United States
AB: Berea sandstone is a well-studied material known to be nonlinearly elastic. For example, stress-strain measurements for stresses less than 30 MPa are repeatably hysteretic and display end-point memory. In an effort to understand the energy scales of the mechanisms causing nonlinear elasticity in Berea sandstone, we have studied the temperature dependence of sample resonances. Resonances are related to the elastic moduli of a sample, and thus indicate whether or not a sample is hardening or softening as a function of temperature. We find that for temperatures in the range 100 K -- 330 K, sample resonance frequencies display significant hysteresis, and several unusual behaviors. Elastic softening is observed as temperature decreases, rather than the expected monotonic increase. In addition, while measurements are repeatable, they are rate dependent on a timescale much longer than the calculated timescale for temperature equilibrium across the sample. It is our hypothesis that this unusual elastic behavior and the slow onset of thermal equilibrium arises from the granular nature of the material. A series of time and temperature dependent experiments was designed and executed to investigate this hypothesis. We will discuss the results of these measurements and their implications for future research.
DE: 5102 Acoustic properties
DE: 5112 Microstructure
DE: 5120 Plasticity, diffusion, and creep
DE: 5134 Thermal properties
DE: 5144 Wave attenuation
SC: Tectonophysics [T]
MN: 2003 Fall Meeting