Characteristics of Laser-Generated Visco-Elastic Rayleigh Waves

2013 ◽  
Vol 543 ◽  
pp. 22-25
Author(s):  
Qing Bang Han ◽  
Jian Li ◽  
Hao Wang ◽  
Chang Ping Zhu
Keyword(s):  
Elastic Modulus ◽  
Transient Response ◽  
Rayleigh Waves ◽  
Laser Ultrasonics ◽  
Normal Displacement ◽  
Space Structures ◽  
Propagation Characteristics ◽  
Elastic Parameters ◽  
Kelvin Model ◽  
Dispersion And Attenuation

This paper reports on a study of the propagation characteristics of visco-elastic, Rayleigh waves induced by laser ultrasonics in half space structures. Beginning with the Kelvin model, the characterization equation and the normal displacement of visco-elastic Rayleigh waves in are derived and the influence of the visco-elastic modulus on dispersion and attenuation are discussed. The transient response of a visco-elastic Rayleigh wave is also simulated by means of Laplace and Hankel inversion transforms. The papers results and conclusions will provide insights and guidance for estimating visco-elastic parameters

EXPERIMENTAL RESEARCH ON VISCOELASTICITY PROPERTY OF DIFFERENT LAYERS PERIODONTAL LIGAMENT UNDER COMPRESSION

2021 ◽  
pp. 2150050
Author(s):  
JINLAI ZHOU ◽  
YANG SONG ◽  
CHENGUANG XU ◽  
CHUNQIU ZHANG ◽  
XUE SHI
Keyword(s):  
Elastic Modulus ◽  
Periodontal Ligament ◽  
Creep Compliance ◽  
Relaxation Modulus ◽  
Maxwell Model ◽  
Kelvin Model ◽  
Generalized Maxwell Model ◽  
Relaxation Stress ◽  
Generalized Kelvin Model ◽  
Fitting Accuracy

The periodontal ligament (PDL) exhibits different material mechanical properties along the long axis of the teeth. To explore the creep and the relaxation effects of dissimilar layers of PDL, this paper took the central incisors of porcine mandibular as experimental subjects and divided them perpendicular to the teeth axis into five layers. Creep experiments and relaxation experiments on five layers were conducted to obtain the creep compliance and relaxation modulus at different layers. Linear elastic model, generalized Kelvin model, and generalized Maxwell model were used to describe the major characteristics of the PDL: Instantaneous elasticity, creep and relaxation. Fitting accuracy of three-parameter, five-parameter, and seven-parameter of the model was compared, and the constitutive equations of different layers were established by the least square method. The results presented that the creep strain and the relaxation stress of PDL were exponentially correlated with time under different loading conditions. Different layers showed a significant effect on the creep strain and relaxation stress of PDL. Along the long axis of the teeth, the changing rule of the creep compliance and relaxation modulus of each layer showed quite the contrary, and the instantaneous elastic modulus first decreased to the minimum, then increased to the maximum. Higher instantaneous elastic modulus led to lower creep compliance and higher relaxation modulus. The generalized Kelvin model and the generalized Maxwell model well characterized the creep and relaxation properties of PDL. Fitting accuracy increased with the number of model parameters. The relaxation time of PDL was about one order of magnitude shorter than the creep retardation time, which indicated that the relaxation effect lasted shorter than the creep effect.

scholarly journals Analysis of Viscoelastic Behavior of Polypropylene/Carbon Nanotube Nanocomposites by Instrumented Indentation

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2535
Author(s):  
Felicia Stan ◽  
Adriana-Madalina Turcanu (Constantinescu) ◽  
Catalin Fetecau
Keyword(s):  
Elastic Modulus ◽  
Carbon Nanotube ◽  
Viscoelastic Behavior ◽  
Creep Function ◽  
Indentation Hardness ◽  
Indentation Modulus ◽  
Shear Creep ◽  
Kelvin Model ◽  
Indentation Tests ◽  
Mwcnt Loading

In this work, the viscoelastic behavior of polypropylene (PP)/multi-walled carbon nanotube (MWCNT) nanocomposites was investigated by indentation testing and phenomenological modeling. Firstly, indentation tests including two-cycle indentation were carried out on PP/MWCNT nanocomposite with three MWCNT loadings (1, 3 and 5 wt %). Next, the Maxwell–Voigt–Kelvin model coupled with two-cycle indentation tests was used to predict the shear creep compliance function and the equivalent indentation modulus. The indentation hardness and elastic modulus of the PP/MWCNT nanocomposites extracted based on the Oliver and Pharr method were compared with the equivalent indentation modulus predicted based on the Maxwell–Voigt–Kelvin mode. The experimental results indicated that the addition of nanotubes into the polypropylene has a positive effect on the micro-mechanical properties of PP/MWCNT nanocomposites. Indentation hardness and elastic modulus increased significantly with increasing MWCNT loading. The creep resistance at the micro-scale of the PP/MWCNT nanocomposites improved with the addition of MWCNTs, with creep displacement reduced by up to 20% by increasing the carbon nanotube loading from 1 to 5 wt %. The Maxwell–Voigt–Kelvin model with three and five Voigt–Kelvin units accurately predicted the shear creep function and its change with increasing MWCNT loading. However, the equivalent indentation modulus was found to be sensitive to the number of Voigt–Kelvin units: the more Voigt–Kelvin units, the better the model predicts the equivalent indentation modulus.

scholarly journals Near surface reconstruction using the full waveform inversion method: a resolution analysis

2016 ◽  
pp. 487-499
Author(s):  
К.Г. Гадыльшин ◽  
Д.А. Неклюдов ◽  
И.Ю. Сильвестров
Keyword(s):  
Rayleigh Waves ◽  
Waveform Inversion ◽  
Observation System ◽  
Inversion Method ◽  
Elastic Model ◽  
Full Waveform Inversion ◽  
Elastic Parameters ◽  
Near Surface ◽  
Full Waveform ◽  
Resolution Analysis

Изучается влияние волны Рэлея на результат обращения полного волнового поля. Показано, что разрешающая способность борновского оператора выше в случае отсутствия рэлеевских волн в наблюдаемых данных. Предложен численный алгоритм, позволяющий анализировать влияние различных параметров обратной динамической задачи сейсмики на результат восстановления верхней части геологического разреза: геометрии системы наблюдений, частотного диапазона, параметризации упругой модели и др. В качестве демонстрационного примера показано, что для поверхностной системы наблюдений в задаче реконструкции макроскоростного строения среды наиболее приемлема параметризация упругой модели через скорости продольных и поперечных волн и плотность. The effect of the Rayleigh wave on full waveform inversion (FWI) is studied. It is shown that the Born operator resolution is better when the Rayleigh waves are not taken into account. A numerical algorithm to analyze the influence of different parameters of the inverse dynamical seismic problem (such as source/receiver geometry, frequency range, elastic model parametrization, etc.) on the near-surface geological section reconstruction is proposed. As a demonstrative example, we show that the best elastic parameters for macrovelocity reconstruction via FWI for a subsurface observation system are P- and S-velocities and density.

ON THE PROPAGATION OF RAYLEIGH WAVES ON THE SURFACE OF A VISCO‐ELASTIC SOLID

Geophysics ◽  
1953 ◽  
Vol 18 (1) ◽  
pp. 70-74 ◽  
Author(s):  
C. W. Horton
Keyword(s):  
Rayleigh Waves ◽  
Dimensionless Parameter ◽  
Attenuation Factor ◽  
Wave Length ◽  
Elastic Solid ◽  
Angular Frequency ◽  
Elastic Parameters ◽  
Lissajous Figure ◽  
The Waves ◽  
Horizontal Displacements

The propagation of Rayleigh waves over the surface of a visco‐elastic solid is examined. It is shown that for a Poisson solid (λ=μ), the behavior of the waves can be characterized by a dimensionless parameter δ=ωη/μ which is less than 0.1 for the frequencies and elastic parameters of interest in geophysics. In this expression ω=angular frequency, μ=shear modulus, η=viscosity. For small values of δ it is possible to modify the usual analysis of Rayleigh waves and obtain the new characteristics without much difficulty. It is shown that the motion of a particle on the earth’s surface is changed from an ellipse to a Lissajous’ figure and that the phase angle between the vertical and horizontal displacements is changed from [Formula: see text] to [Formula: see text] radians. The surface wave has an attenuation factor of [Formula: see text] where [Formula: see text] is the wave length of the Rayleigh wave in the absence of internal friction.

Effects of graphite porosity and anisotropy on measurements of elastic modulus using laser ultrasonics

2014 ◽  
Author(s):  
James B Spicer ◽  
Fan W Zeng ◽  
Karen Han ◽  
Lauren R Olasov ◽  
Nidia C Gallego ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Laser Ultrasonics

Lamb Wave Propagation Through Off-Axis Media

2011 ◽  
Author(s):  
Jacob Brown ◽  
Whitney Reynolds ◽  
Derek Doyle ◽  
Andrei Zagrai
Keyword(s):  
Wave Propagation ◽  
Elastic Wave ◽  
Wave Velocity ◽  
Lamb Wave ◽  
Composite Structures ◽  
Lamb Waves ◽  
Resin Matrix ◽  
Space Structures ◽  
Propagation Characteristics ◽  
Lamb Wave Propagation

The use of elastic wave based Structural Health Monitoring has shown its usefulness in both characterizing and diagnosing composite structures. Techniques using elastic wave SHM are being developed to allow for improved efficiency and assurance in all stages of space structure development and deployment. These techniques utilize precise understanding of wave propagation characteristics to extract meaningful information regarding the health and validity of a component, assembly, or structure. However, many of these techniques focus on the diagnostic of traditional, isotropic materials, and questions remain as to the effect of the orthotropic properties of resin matrix composite material on the propagation of elastic waves. As the demands and expectations placed upon composite structures continue to expand in the space community, these questions must be addressed to allow the development of elastic wave based SHM techniques that will enable advancements in areas such as automated build validation and qualification, and in-situ characterization and evaluation of increasingly complex space structures. This study attempts to aid this development by examines the effect of cross ply, off-axis fiber orientation on the propagation characteristics of lamb waves. This is achieved by observing the result of symmetric and anti-symmetric wave propagation across materials in cases containing both off-axis and axially-aligned elements. In both cases the surface plies of the test specimen are axially aligned with the wave propagation direction. Using these results, the relative effect of core ply orientation on lamb wave propagation, and lamb wave sensitivity to bulk properties, or alternatively, the dominance of surface properties on propagation characteristics, can be seen, and this information can be used to aid in future research and application of lamb waves for interrogation of advanced, high-strain composite space structures. It was found that the core orientation caused significant variation in the S0 wave velocity, while yielding little influence on the A0 wave velocity.

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