Quasistatic loading of Berea sandstone

Запропонована феноменологiчна модель для опису властивостей напруження-деформацiя пiсковика пiд дiєю повiльного навантаження. Розглянута комбiнацiя трьох механiзмiв, якi пов’язуються з внутрiшнiми обмiнними процесами: механiзм стандартного релаксуючого твердого тiла, пружний механiзм з прилипанням, механiзм залишкової пластичної деформацiї. З малою кiлькiстю параметрiв модель вiдтворює як якiсно, так i кiлькiсно головнi експериментальнi данi по напруженню-деформацiї для пiсковика Береа. Модель правильно вiдтворює великi та малi петлi на траєкторiї напруження-деформацiя (пам’ять про кiнцеву точку). Власне запропонована залежнiсть деформацiї вiд напруження є не чим iншим, як рiвнянням стану пiсковика

Physical properties and mantle dynamics

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Because planetary interiors are remote, laboratory methods and associated theory are an essential step for interpreting geophysical measurements in terms of quantities that are needed for understanding Earth--temperature, composition, stress state, history, and hazards. One objective is the study of minerals and rocks as materials using experimental methods; another is to develop new methods, as in high pressure research, codes for computation in rock/soil physics, or nuclear-based analysis. Accomplishments include developing a single-crystal x-ray diffraction apparatus with application to materials at extremely high pressure and temperature; P-V-T equations of state and seismic velocity measurements for understanding the composition of Earth`s outer 1,000 km; creating computational tools to explain complex stress-strain histories of rocks; and measuring tungsten/thorium ratios W/Th that agree with the hypothesis that Earth accreted heterogeneously. Work performed in this project applies to geosciences, geothermal energy, mineral and rock properties, seismic detection, and isotope dating

Minerals of the earth's deep interior

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The project addresses the major geophysical issue of the nature of the seismic velocity and density discontinuity at 670 km depth (the boundary between upper and lower mantle with temperature about 1,900 K and pressure about 23 GPa). A phase change at this depth would represent a relatively small barrier to mantle convection through the discontinuity, but compositional change would inhibit thermal convection throughout the mantle. To address this problem the authors measured equation of state parameters in mantle minerals as functions of high P-T using single crystal x-ray diffraction with a unique, new diamond-anvil cell (DAC) at simultaneous high temperature and pressure. Single-crystal diffraction improves absolute accuracy in lattice constants over those from powder diffraction by a factor of 5 to 10. The authors have measured equations of state of orthoenstatite MgSiO{sub 3} and hexagonal boron nitride hBN

Pulse-mode measurement of harmonic generation in rock

One goal in our research is to quantify frequency content modification caused by nonlinear elasticity that may take place during seismic wave propagation. To this end, we have conducted ultrasonic experiments in rock, analogous to those conducted in gas, for study of spectral changes from harmonic generation that take place along the wave path. For a material with cubic anharmonicity, the amplitude of the 2[omega] harmonic is shown to be proportional to xk[sup 2]U[sup 2], where [omega] is the angular frequency, x is the propagation distance, k is the wave vector, and U is the displacement amplitude at [omega]. Experiments in sandstone focused on confirming this result showed that U[sub 2[omega]] was linearly proportional to distance x. At fixed x, the amplitude of [omega] scaled as frequency squared (k[sup 2]) and as sourceamplitude squared (U[sup 2]). Thus the fundamental prediction of the 2[omega] harmonic in rock with cubic anharmonicity was confirmed. The compressional nonlinear modulus [Beta] was measured to be [minus]7[times]10[sup 3]+/[minus]23%