Wyniki wyszukiwania - Biblioteka Nauki

1

Analytical investigation of strain loading frequency effect on stress-strain-temperature relationship of shape-memory alloy

100%

Ikeda T.

Archives of Mechanics

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2015

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tom Vol. 67, nr 4

275--291

EN

In this paper a set of simple governing equations of shape-memory alloys was derived by introducing some assumptions and a formula giving temperature variation was obtained by integrating one of the governing equations. The factors affecting the temperature variation depending on loading frequency were analytically investigated from the formula. The obtained temperature variation agreed qualitatively with the measured data. The calculated stress-strain-temperature relationship also agreed qualitatively with the measured data. It was found from the formula that the temperature vibrates sinusoidally and approaches a certain value asymptotically, and that the temperature variation is affected by the ratio of frequency to heat transfer and the ratio of latent heat to generated heat.

2

Frequency and temperature dependent transport properties of NiCuZn ceramic oxide

86%

Hossen M. B. , Hossain A. K. M. A.

Materials Science Poland

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2015

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tom Vol. 33, No. 2

259--267

EN

A polycrystalline sample of ceramic oxide Ni0:27Cu0:10Zn0:63Fe2O4 was prepared by the solid state reaction method. The sintered sample was well polished to remove any oxide layer formed during sintering and the two surfaces of the pellet were coated with a silver paste as a contact material. Among dielectric properties, complex dielectric constant (ε* = ε' - jε"), loss tangent (tanδ) and ac conductivity (σac) in the frequency range of 20 Hz to 2 MHz were analyzed in the temperature range of 303 to 498 K using a Wayne Kerr impedance analyzer (model No. 6500B). The experimental results indicate that ε', ε", tanδ and σacdecrease with an increase in frequency and increase with increasing temperature. The transition temperature, as obtained from dispersion curve of ε', shifts towards higher temperature with an increase in frequency. The variation of dielectric properties with frequency and temperature shows the dispersion behavior which is explained in the light of Maxwell-Wagner type of interfacial polarization in accordance with the Koop’s phenomenological theory. The frequency dependent conductivity results satisfy the Jonscher’s power law, σT (ω) = σ(o)+Aωn, and the results show the occurrence of two types of conduction process at elevated temperature: (i) low frequency conductivity, due to long-range ordering (frequency independent, region I), (ii) mid frequency conductivity at the grain boundaries (region II, dispersion) and (iii) high frequency conductivity at the grain interior due to the short-range hopping mechanism (frequency independent plateau, region III).

3

Experimental study and modelling the evolution of viscoelastic hysteresis loop at different frequencies in myocardial tissue

72%

Smoluk A. , Smoluk L. , Lisin R. , Protsenko Y.

Acta of Bioengineering and Biomechanics

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2017

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tom Vol. 19, no. 3

11--17

EN

Our work involved experimental study of the influence of actomyosin complexes and the main structural components of the myocardial tissue – connective tissue collagen framework and cardiomyocytes – on the characteristics of viscoelastic hysteresis at different frequencies. In this paper a new method was introduced for the analysis of the viscoelastic characteristics of the force hysteresis in the isolated myocardial preparation for the assessment of mechanical energy expenditure in the tension-compression cycle. We established that basic myocardial structures have an impact on the to the characteristics of the viscoelastic hysteresis in many ways. It was shown that in rat’s myocardium cardiomyocytes one main factor that define the stiffness and viscosity of the myocardium in the physiological range of deformations, while binding of calcium ions with EGTA and calcium removal of sarcoplasmic reticulum with caffeine reduces viscoelasticity by ~30% and collagen framework is responsible for about 10% of viscoelasticity. It was revealed that in the physiological range of the hysteresis frequencies (3 to 7 Hz) expenditure of mechanical energy per unit of time increases linearly with increasing frequency. We proposed the structural and functional model that adequately describes the characteristics of the viscoelastic hysteresis in myocardial preparation in the range of strains and frequencies being under study.

4

Extracting static elastic moduli of rock through elastic wave velocities

72%

Zhang Y. , Gu Y. , Zhou H. , Yang L.

Acta Geophysica

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2024

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tom Vol. 72, no. 2

915--931

EN

In many geological conditions, obtaining the static elastic moduli of crustal rocks is an essential subject for accurate mechanical analyses of crust. The elastic wave method may be the best choice if rock specimens cannot be taken since elastic wave propagation can be applied to in-situ environments. Although many signs of progress have been made in the elastic wave method, some issues still restrict the accurate extraction of static moduli and its applications. A review of this method and its further research prospect is urgently needed. With this purpose, this paper summarized and analyzed the published experimental data about the relationship between the static and dynamic Young’s moduli of rock, and the frequency dependence of wave velocities and dynamic elastic moduli. P- and S-wave velocities, Young’s, and bulk moduli of rock, especially the saturated rock, have strong frequency dependence in a wide frequency range of 10-6-106 Hz. Different rocks or conditions (such as water content, amplitude, and pressure), have different frequency-dependent characteristics. The current elastic wave method can be classified into two methods: the empirical correlation method and the multifrequency ultrasonic method. The basic principle, advantages, and disadvantages of both methods are analyzed. Especially, the reasonability of the multifrequency ultrasonic method was elaborated given the nonlinear elasticity, strain level/rate, and pores/cracks in rock materials. Existing problems and prospects on the two methods are also pointed out, such as the choice of a proper empirical correlation, accurate determination of the critical P- and S-wave velocities, the prediction of Young’s modulus at each strain level, and the reasonability of the method under various water contents and fracture structures.

5

Fluid identification based on P-wave anisotropy dispersion gradient inversion for fractured reservoirs

58%

Zhang J. W. , Huang H. D. , Zhu B. H. , Liao W.

Acta Geophysica

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2017

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tom Vol. 65, no. 5

1081--1093

EN

Fluid identification in fractured reservoirs is a challenging issue and has drawn increasing attentions. As aligned fractures in subsurface formations can induce anisotropy, we must choose parameters independent with azimuths to characterize fractures and fluid effects such as anisotropy parameters for fractured reservoirs. Anisotropy is often frequency dependent due to wave-induced fluid flow between pores and fractures. This property is conducive for identifying fluid type using azimuthal seismic data in fractured reservoirs. Through the numerical simulation based on Chapman model, we choose the P-wave anisotropy parameter dispersion gradient (PADG) as the new fluid factor. PADG is dependent both on average fracture radius and fluid type but independent on azimuths. When the aligned fractures in the reservoir are meter-scaled, gas-bearing layer could be accurately identified using PADG attribute. The reflection coefficient formula for horizontal transverse isotropy media by Rüger is reformulated and simplified according to frequency and the target function for inverting PADG based on frequency-dependent amplitude versus azimuth is derived. A spectral decomposition method combining Orthogonal Matching Pursuit and Wigner–Ville distribution is used to prepare the frequency-division data. Through application to synthetic data and real seismic data, the results suggest that the method is useful for gas identification in reservoirs with meter-scaled fractures using high-qualified seismic data.