Low-frequency seismic properties of thermally cracked and argon-saturated granite

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. F147-F159 ◽  
Author(s):  
Cao Lu ◽  
Ian Jackson
Keyword(s):  
Shear Modulus ◽  
Transient Flow ◽  
Crack Density ◽  
Fluid Pressure ◽  
Low Frequency ◽  
Confining Pressure ◽  
Seismic Properties ◽  
Aspect Ratios ◽  
In Situ Permeability

Torsional forced-oscillation techniques have been used to measure the shear modulus and strain-energy dissipation on cylindrical specimens of a fine-grained granite, Delegate aplite. The specimens were subjected to thermal cycling and associated microcracking under varying conditions of confining pressure [Formula: see text] and argon pore-fluid pressure [Formula: see text] within the low-frequency saturated isobaric regime. Complementary transient-flow studies of in-situ permeability and volumetric measurements of connected crack porosity allowed the modulus measurements to be interpreted in terms of the density and interconnectivity of the thermally generated cracks. The modulus measurements indicate that newly generated thermal cracks are closed by a differential pressure, [Formula: see text], which ranges from [Formula: see text] for temperatures of [Formula: see text]. This suggests crack aspect ratios on the order of [Formula: see text]. The covariation of in-situ permeability [Formula: see text] and thermal crack density [Formula: see text] that we infer from the modulus deficit is consistent with percolation theory. There is a well-defined threshold at [Formula: see text], beyond which [Formula: see text] increases markedly as [Formula: see text], with [Formula: see text]. At lower crack densities, it is difficult to measure the sensitivity of shear modulus to variations of confining and pore pressures because pore-pressure equilibrium is approached so sluggishly. At temperatures beyond the percolation threshold, the modulus variation is a function of the effective pressure, [Formula: see text], with the value of [Formula: see text] increasing toward one with increasing crack connectivity.

Low-frequency seismic properties of olivine-orthopyroxene mixtures

2020 ◽  
Author(s):  
Tongzhang Qu ◽  
Ian Jackson ◽  
Ulrich Faul
Keyword(s):  
Shear Modulus ◽  
Upper Mantle ◽  
Forced Oscillation ◽  
Low Frequency ◽  
Secondary Phase ◽  
Confining Pressure ◽  
Creep Function ◽  
Seismic Properties ◽  
New Findings

<p>Although the seismic properties of polycrystalline olivine have been the subject of systematic and comprehensive study at seismic frequencies, the role of orthopyroxene as the major secondary phase in the shallow parts of the Earth’s upper mantle has so far received little attention. Accordingly, we have newly prepared synthetic melt-free polycrystalline specimens containing different proportions of olivine (Ol, Fo<sub>90</sub>) and orthopyroxene (Opx, En<sub>90</sub>) by the solution-gelation method. The resulting specimens, ranging in composition between Ol<sub>95</sub>Opx<sub>5</sub> and Ol<sub>5</sub>Opx<sub>95</sub> composition, were mechanically tested by torsional forced oscillation at temperatures of 1200 ºC to 400 ºC accessed during staged cooling under a confining pressure of 200 MPa. The microstructures of tested specimens were evaluated by BSE, EBSD and TEM. The forced-oscillation data, i.e. shear modulus and associated strain-energy dissipation at 1-1000 s period, were closely fitted by a model based on an extended Burgers-type creep function. This model was also required to fit data from previous ultrasonic and Brillouin spectroscopic measurements at ns-µs periods. Within the observational window (1-1000 s), the shear modulus and dissipation vary monotonically with period and temperature for each of the tested specimens, which is broadly comparable with that previously reported for olivine-only samples. There is no evidence of the superimposed dissipation peak reported by Sundberg and Cooper (2010) for an Ol<sub>60</sub>Opx<sub>40</sub> specimen prepared from natural precursor materials and containing a melt fraction of 1.5%. The higher orthopyroxene concentrations are associated with systematically somewhat lower levels of dissipation and corresponding weaker modulus dispersion. The new findings suggest that the olivine-based model for high-temperature viscoelasticity in upper-mantle olivine requires only modest modification to accommodate the role of orthopyroxene, including appropriate compositional dependence of the unrelaxed modulus and its temperature derivative.</p>

Modeling wave propagation in cracked porous media with penny-shaped inclusions

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. WA141-WA151 ◽  
Author(s):  
Lin Zhang ◽  
Jing Ba ◽  
José M. Carcione ◽  
Weitao Sun
Keyword(s):  
Wave Propagation ◽  
Aspect Ratio ◽  
Crack Density ◽  
Low Frequency ◽  
Confining Pressure ◽  
Wave Dispersion ◽  
Fluid Viscosity ◽  
Porous Rocks ◽  
Flow Models ◽  
Dispersion And Attenuation

Understanding acoustic wave dispersion and attenuation induced by local (squirt) fluid flow between pores and cracks (compliant pores) is fundamental for better characterization of the porous rocks. To describe this phenomenon, some squirt-flow models have been developed based on the conservation of the fluid mass in the fluid mechanics. By assuming that the cracks are represented by isotropically distributed (i.e., randomly oriented) penny-shaped inclusions, this study applies the periodically oscillating squirt flow through inclusions based on the Biot-Rayleigh theory, so that the local squirt flow and global wave oscillation of rock are analyzed in the same theoretical framework of Hamilton’s principle. The governing wave-propagation equations are derived by incorporating all of the crack characteristics (such as the crack radius, crack density, and aspect ratio). In comparison with the previous squirt models, our model predicts the similar characteristics of wave velocity dispersion and attenuation, and our results are in agreement with Gassmann equations at the low-frequency limit. In addition, we find that the fluid viscosity and crack radius only affect the relaxation frequency of the squirt-flow attenuation peak, whereas the crack density and aspect ratio also affect the magnitudes of dispersion and attenuation. The application of this study to experimental data demonstrates that when the differential pressure (the difference between confining pressure and pore pressure) increases, the closure of cracks can lead to a decrease of attenuation. The results confirm that our model can be used to analyze and interpret the observed wave dispersion and attenuation of real rocks.

scholarly journals Fluid pressure heterogeneity during fluid flow in rocks: new laboratory measurement device and method

2021 ◽  
Vol 225 (2) ◽  
pp. 968-983
Author(s):  
Nicolas Brantut ◽  
Franciscus M Aben
Keyword(s):  
Pore Pressure ◽  
Transient Flow ◽  
Fluid Pressure ◽  
Confining Pressure ◽  
Dead Volume ◽  
Low Permeability ◽  
Pore Fluid Pressure ◽  
Working Pressure ◽  
New Type ◽  
Internal Pore

SUMMARY We present a new type of transducer capable of measuring local pore fluid pressure in jacketed rock samples under elevated confining pressure conditions. The transducers are passive (strain-gauge based), of small size (7 mm in diameter at the contact with the rock and around 10 mm in length), and have minimal dead volume (a few mm3). The transducers measure the differential pressure between the confining fluid and the internal pore pressure. The design is easily adaptable to tune the sensitivity and working pressure range up to several hundred megapascals. An array of four such transducers was tested during hydrostatic pressurization cycles on Darley Dale sandstone and Westerly granite. The prototypes show very good linearity up to 80 MPa with maximum deviations of the order of 0.25 MPa, regardless of the combination of pore and confining pressure. Multiple internal pore pressure measurements allow us to quantify the local decrease in permeability associated with faulting in Darley Dale sandstone, and also prove useful in tracking the development of pore pressure fronts during transient flow in low permeability Westerly granite.

scholarly journals Chlorosulfuric acid-assisted production of functional 2D materials

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Mohsen Moazzami Gudarzi ◽  
Maryana Asaad ◽  
Boyang Mao ◽  
Gergo Pinter ◽  
Jianqiang Guo ◽  
...  
Keyword(s):  
Hexagonal Boron Nitride ◽  
2D Materials ◽  
Real Life ◽  
Large Area ◽  
Polar Solvents ◽  
Aspect Ratios ◽  
Two Dimensional Materials ◽  
Liquid Phase Exfoliation

AbstractThe use of two-dimensional materials in bulk functional applications requires the ability to fabricate defect-free 2D sheets with large aspect ratios. Despite huge research efforts, current bulk exfoliation methods require a compromise between the quality of the final flakes and their lateral size, restricting the effectiveness of the product. In this work, we describe an intercalation-assisted exfoliation route, which allows the production of high-quality graphene, hexagonal boron nitride, and molybdenum disulfide 2D sheets with average aspect ratios 30 times larger than that obtained via conventional liquid-phase exfoliation. The combination of chlorosulfuric acid intercalation with in situ pyrene sulfonate functionalisation produces a suspension of thin large-area flakes, which are stable in various polar solvents. The described method is simple and requires no special laboratory conditions. We demonstrate that these suspensions can be used for fabrication of laminates and coatings with electrical properties suitable for a number of real-life applications.

scholarly journals Moduli and modes in the Mikado model

Soft Matter ◽  
2021 ◽  
Author(s):  
Brian Tighe ◽  
Karsten Baumgarten
Keyword(s):  
Shear Modulus ◽  
Mechanical Model ◽  
Low Frequency ◽  
Vibrational Modes ◽  
Prior Work ◽  
Fiber Networks ◽  
Elastic Shear Modulus ◽  
Flexible Fiber ◽  
Elastic Shear

We determine how low frequency vibrational modes control the elastic shear modulus of Mikado networks, a minimal mechanical model for semi-flexible fiber networks. From prior work it is known that...

scholarly journals Hearing at threshold intensities: by slow mechanical traveling waves or by fast cochlear fluid pressure waves

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Haim Sohmer
Keyword(s):  
Soft Tissue ◽  
Hair Cells ◽  
Traveling Wave ◽  
Basilar Membrane ◽  
Fluid Pressure ◽  
Low Frequency ◽  
Frequency Discrimination ◽  
Outer Hair Cells ◽  
Common Mechanism ◽  
Frequency Stimulation

The three modes of auditory stimulation (air, bone and soft tissue conduction) at threshold intensities are thought to share a common excitation mechanism: the stimuli induce passive displacements of the basilar membrane propagating from the base to the apex (slow mechanical traveling wave), which activate the outer hair cells, producing active displacements, which sum with the passive displacements. However, theoretical analyses and modeling of cochlear mechanics provide indications that the slow mechanical basilar membrane traveling wave may not be able to excite the cochlea at threshold intensities with the frequency discrimination observed. These analyses are complemented by several independent lines of research results supporting the notion that cochlear excitation at threshold may not involve a passive traveling wave, and the fast cochlear fluid pressures may directly activate the outer hair cells: opening of the sealed inner ear in patients undergoing cochlear implantation is not accompanied by threshold elevations to low frequency stimulation which would be expected to result from opening the cochlea, reducing cochlear impedance, altering hydrodynamics. The magnitude of the passive displacements at threshold is negligible. Isolated outer hair cells in fluid display tuned mechanical motility to fluid pressures which likely act on stretch sensitive ion channels in the walls of the cells. Vibrations delivered to soft tissue body sites elicit hearing. Thus, based on theoretical and experimental evidence, the common mechanism eliciting hearing during threshold stimulation by air, bone and soft tissue conduction may involve the fast-cochlear fluid pressures which directly activate the outer hair cells.

scholarly journals Atmospheric Ice Particle Shape Estimates from Polarimetric Radar Measurements and In Situ Observations

2017 ◽  
Vol 34 (12) ◽  
pp. 2569-2587 ◽  
Author(s):  
Sergey Y. Matrosov ◽  
Carl G. Schmitt ◽  
Maximilian Maahn ◽  
Gijs de Boer
Keyword(s):  
Aspect Ratio ◽  
Particle Shape ◽  
Characteristic Size ◽  
In Situ Measurements ◽  
Department Of Energy ◽  
Depolarization Ratio ◽  
Suggested Approach ◽  
Aspect Ratios ◽  
Radar Measurements

AbstractA remote sensing approach to retrieve the degree of nonsphericity of ice hydrometeors using scanning polarimetric Ka-band radar measurements from a U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program cloud radar operated in an alternate transmission–simultaneous reception mode is introduced. Nonsphericity is characterized by aspect ratios representing the ratios of particle minor-to-major dimensions. The approach is based on the use of a circular depolarization ratio (CDR) proxy reconstructed from differential reflectivity ZDR and copolar correlation coefficient ρhυ linear polarization measurements. Essentially combining information contained in ZDR and ρhυ, CDR-based retrievals of aspect ratios are fairly insensitive to hydrometeor orientation if measurements are performed at elevation angles of around 40°–50°. The suggested approach is applied to data collected using the third ARM Mobile Facility (AMF3), deployed to Oliktok Point, Alaska. Aspect ratio retrievals were also performed using ZDR measurements that are more strongly (compared to CDR) influenced by hydrometeor orientation. The results of radar-based retrievals are compared with in situ measurements from the tethered balloon system (TBS)-based video ice particle sampler and the ground-based multiangle snowflake camera. The observed ice hydrometeors were predominantly irregular-shaped ice crystals and aggregates, with aspect ratios varying between approximately 0.3 and 0.8. The retrievals assume that particle bulk density influencing (besides the particle shape) observed polarimetric variables can be deduced from the estimates of particle characteristic size. Uncertainties of CDR-based aspect ratio retrievals are estimated at about 0.1–0.15. Given these uncertainties, radar-based retrievals generally agreed with in situ measurements. The advantages of using the CDR proxy compared to the linear depolarization ratio are discussed.

Mechanical behaviour of powders using a medium pressure flexible boundary cubical triaxial tester

2003 ◽  
Vol 217 (3) ◽  
pp. 233-241 ◽  
Author(s):  
F Li ◽  
V M Puri
Keyword(s):  
Shear Modulus ◽  
Mechanical Behaviour ◽  
Triaxial Compression ◽  
Three Dimensional ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Alumina Powder ◽  
Medium Pressure ◽  
Mean Pressure ◽  
Confining Pressures

A medium pressure (<21 MPa) flexible boundary cubical triaxial tester was designed to measure the true three-dimensional response of powders. In this study, compression behaviour and strength of a microcrystalline cellulose powder (Avicel® PH102), a spray-dried alumina powder (A16SG), and a fluid-bed-granulated silicon nitride based powder (KY3500) were measured. To characterize the mechanical behaviour, three types of triaxial stress paths, that is, the hydrostatic triaxial compression (HTC), the conventional triaxial compression (CTC), and the constant mean pressure triaxial compression (CMPTC) tests were performed. The HTC test measured the volumetric response of the test powders under isostatic pressure from 0 to 13.79MPa, during which the three powders underwent a maximum volumetric strain of 40.8 per cent for Avicel® PH102, 30.5 per cent for A16SG, and 33.0 per cent for KY3500. The bulk modulus values increased 6.4-fold from 57 to 367MPa for Avicel® PH102, 3.7-fold from 174 to 637 MPa for A16SG, and 8.1-fold from 74 to 597MPa for KY3500, when the isotropic stress increased from 0.69 to 13.79 MPa. The CTC and CMPTC tests measured the shear response of the three powders. From 0.035 to 3.45MPa confining pressure, the shear modulus increased 28.7-fold from 1.6 to 45.9MPa for Avicel® PH102, 35-fold from 1.7 to 60.5MPa for A16SG, and 28.5-fold from 1.5 to 42.8MPa for KY3500. In addition, the failure stresses of the three powders increased from 0.129 to 4.41 MPa for Avicel® PH102, 0.082 to 3.62 MPa for A16SG, and 0.090 to 4.66MPa for KY3500, respectively, when consolidation pressure increased from 0.035 to 3.45MPa. In addition, the shear modulus and failure stress values determined from the CTC test at 2.07, 2.76, and 3.45MPa confining pressures are consistently greater than those from the CMPTC test at the same constant mean pressures. This observation demonstrates the influence of stress paths on material properties. The CTT is a useful tool for characterizing the three-dimensional response of powders and powder mixtures.

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