Elastic waves Research Papers - Academia.edu (original) (raw)

A series of experiments were performed to further investigate the phenomenon of shear-banding in surfactant solutions. Many surfactant solutions, through their unique amphiphilic chemistry, form long wormlike micelle structures which... more

A series of experiments were performed to further investigate the phenomenon of shear-banding in surfactant solutions. Many surfactant solutions, through their unique amphiphilic chemistry, form long wormlike micelle structures which behave like living polymers. These wormlike micelles have interesting viscoelastic properties and have been the subject of a number of recent studies. These water-based surfactant systems are widely used in

Упругие волны это векторные волны смещений материальных точек. В отличии от элек-тромагнитных волн они могут быть и поперечными и продольными. Обычно для них записывают разные уравнения. Здесь такого разделения не будет. При наличии... more

Упругие волны это векторные волны смещений материальных точек. В отличии от элек-тромагнитных волн они могут быть и поперечными и продольными. Обычно для них записывают разные уравнения. Здесь такого разделения не будет. При наличии поверхно-сти раздела между двумя разными средами граничные условия определяются не самими уравнениями, а некоторыми дополнительными условиями. Большой интерес представля-ют поверхностные волны, особенно в связи с землетрясениями, а также волны в анизо-тропных средах. Здесь так же, как в электродинамике, удается построить решения в виде плоских волн, что облегчает исследование процессов отражения от упругих пластин. 6.1 Упругие волны в изотропных средах В теории упругости основным объектом является вектор смещения u(r, t) точки r в мо-мент времени t. Компоненты вектора смещения u j (r, t) определяются с помощью уравне-ния ρ ∂ 2 u j (r, t) ∂t 2 = ∂σ jk (r,

This thesis is devoted to the study of the high frequency Dirichlet and Neumann problems for the elasticity system. We study the reflection phenomenon at the boundary by means of two techniques: Gaussian beams summation and Wigner... more

This thesis is devoted to the study of the high frequency Dirichlet and Neumann problems for the elasticity system. We study the reflection phenomenon at the boundary by means of two techniques: Gaussian beams summation and Wigner measures. In chapters 1 and 2, we start by studying the simpler problem of the scalar wave equation with one speed. Under some hypotheses on the initial conditions, we build an approximate solution by a Gaussian beams superposition. Justification of the asymptotics is based on norms estimate of some integral operators with complex phases. For more general initial conditions, we use Wigner measures to compute the microlocal energy density. We compute Wigner transforms of Gaussian beams integrals in an explicit way. The behaviour of the microlocal energy density for the exact solution is deduced from the one for the approximate solution. In chapter 3, we use the established results on infinite sums of Gaussian beams to build an approximate solution for the elasticity equations and to compute its microlocal energy density. We treat new difficulties arising from the existence of two different speeds in the elasticity system.

In this paper we evaluate coating-substrate adherence in galvanized steel with the Acoustic Emission (AE) technique applied during scratch tests (ST), analyzing in this way the elastic waves emitted during microfracture processes. Hot-dip... more

In this paper we evaluate coating-substrate adherence in galvanized steel with the Acoustic Emission (AE) technique applied during scratch tests (ST), analyzing in this way the elastic waves emitted during microfracture processes. Hot-dip galvanized samples were obtained, with different ...

Seismic anisotropy is a key property to understand the structure of the crust and mantle. In this contribution, we investigate the influence of shape (morphological) preferred orientation (SPO), crystallographic preferred orientation... more

Seismic anisotropy is a key property to understand the structure of the crust and mantle. In this contribution, we investigate the influence of shape (morphological) preferred orientation (SPO), crystallographic preferred orientation (CPO) and the spatial distribution of grains on seismic anisotropy in rocks (Bazargan et al., 2018). A numerical toolset has been developed with COMSOL to investigate these effects numerically, which has been benchmarked analytically and against other numerical models. Numerical samples modelled in 2D and 3D can determine anisotropy, by measurements along different sample axes, using different geometrical setups and mineral compositions. This numerical tool can include a variety of mineral arrangements and propagate P and S waves from different directions to calculate anisotropy. Current numerical results confirm directly the relations between the structural framework of the rocks (foliation, lineation) and velocity anisotropy, shear wave splitting and shear wave polarisation. This has been proven numerically with the effects of layering, which represents foliation and lineation in 2D. One of the aims of this work is to apply the fundamental results and effects of effective medium to improve our finite element method (FEM) toolbox to provide a numerical modelling tool for seismic data that have been collected in the field. Since the numerical and laboratory measurements are worked on together to verify the numerical results, to compare the models and explain the laboratory measurements have been conducted. Here we also present laboratory measurements of directional dependence of elastic waves velocity and shear wave splitting to the internal rock structure. In the experimental part of this study, we illustrate the contribution of microstructural parameters (grain sizes, SPO and microcracks) to the elastic anisotropy of relatively similar quartzites and granites. An objective with the laboratory measurements is to investigate the effect of grain size and its possible influence on elastic wave speed and potential scattering effects due to wavelength effects. Granites are the one we use to investigate anisotropy related to SPO and CPO. Our experimental data consist of the measurements of elastic wave velocities (Vp, Vs 1 and Vs 2) at confining pressures up to 600 MPa (Bazargan et al., 2019). numerical modelling together with laboratory measurements are used to obtain a better understanding of the role of microstructures in elastic wave propagation and its anisotropy

A simple method for preparing artificial kidney stones with varying physical properties is described. BegoStone was prepared with a powder-to-water ratio ranging from 15:3 to 15:6. The acoustic properties of the phantoms were... more

A simple method for preparing artificial kidney stones with varying physical properties is described. BegoStone was prepared with a powder-to-water ratio ranging from 15:3 to 15:6. The acoustic properties of the phantoms were characterized using an ultrasound transmission technique, from which the corresponding mechanical properties were calculated based on elastic wave theory. The measured parameters for BegoStone phantoms of different water contents are: longitudinal wave speed (3,148–4,159 m/s), transverse wave speed (1,813–2,319 m/s), density (1,563–1,995 kg/m3), longitudinal acoustic impedance (4.92–8.30 kg/m2 s), transverse acoustic impedance (2.83–4.63 kg/m2 s), Young’s modulus (12.9–27.4 GPa), bulk modulus (8.6–20.2 GPa), and shear modulus (5.1–10.7 GPa), which cover the range of corresponding properties reported in natural kidney stones. In addition, diametral compression tests were carried out to determine tensile failure strength of the stone phantoms. BegoStone phantoms with varying water content at preparation have tensile failure strength from 6.9 to 16.3 MPa when tested dry and 3.2 to 7.1 MPa when tested in water-soaked condition. Overall, it is demonstrated that this new BegoStone preparation method can be used to fabricate artificial stones with physical properties matched with those of natural kidney stones of various chemical compositions.

Guided elastic waves in the frequency range of a few hundred kHz, generated and detected by appro- priate transducer arrays, are used to monitor the structural integrity of pipes by comparing their actual state with a predefined reference... more

Guided elastic waves in the frequency range of a few hundred kHz, generated and detected by appro- priate transducer arrays, are used to monitor the structural integrity of pipes by comparing their actual state with a predefined reference state. For these purposes, theoretical, numerical, and experimental results are combined to study guided wave propagation and wave interaction with relevant defects in detail. Based on these findings, a guided wave based multi-channel structural health monitoring (SHM) system is designed and applied to identify and monitor structural defects in various piping components. The potential use of synthetic aperture techniques is discussed yielding spatial distributions of damage parameters along the pipe. The results reveal that guided wave based SHM in the kHz frequency regime has great potential for online monitoring of piping systems. It combines imaging techniques with long range detection capabilities and therefore closes the gap between local high...

The detection and characterization of defects in structures is an important issue in non-destructive testing. To avoid the scanning of large samples, guided elastic waves, which propagate along the structure, are excited. These waves... more

The detection and characterization of defects in structures is an important issue in non-destructive testing. To avoid the scanning of large samples, guided elastic waves, which propagate along the structure, are excited. These waves interact with a defect, which results in a scattered wave field. In an experiment, the displacements of these scattered waves are recorded over time for a fixed axial coordinate at a number of circumferential positions of a circular cylindrical tube. Since in complex structures it is difficult to determine the axial and particularly circumferential position of the defect directly from the time signals, a time reversed numerical simulation is performed. There the measured displacement histories are reversed in time and used as displacement excitations in a simulation of the tested structure. A three-dimensional code in cylindrical coordinates, based on a velocity-stress finite-difference method, is used to simulate the wave propagation. As long as the ge...

In order to reduce the costs related to corrosion damage in aircraft structures, it is vital to develop new robust, accurate and reliable damage detection methods. A possible answer to this problem is offered by newly developed nonlinear... more

In order to reduce the costs related to corrosion damage in aircraft structures, it is vital to develop new robust, accurate and reliable damage detection methods. A possible answer to this problem is offered by newly developed nonlinear ultrasonic techniques, which monitors the nonlinear elastic wave propagation behaviour introduced by damage, to detect its presence and location.In this paper, a new nonlinear time reversal technique is presented for the detection and localization of a scattered zone (damage) in a multi-material medium. In particular, numerical findings on a friction stir-welded aluminium plate-like structure are reported. Damage was introduced in the heat affected zone and modelled using a multi-scale material constitutive model (Preisach–Mayergoyz space).Studies were conducted for two different transducer configurations. Particular attention was devoted to find the optimum time-reversed window to be re-emitted in the structures. The methodology was compared with traditional time-reversal acoustics (TRA), showing significant improvements. While the traditional TRA was not able to clearly localise the damage, the developed technique identified in a clear manner the faulted zone, showing its robustness to locate and characterize nonlinear sources, in presence of a multi-material medium.

The paper gives effective use of the elastic and plastic properties of the material pre-stressed in steel beams with a significant increase in dry capacity with a change in the cross section of the upper and lower shelves, reducing... more

The paper gives effective use of the elastic and plastic properties of the material pre-stressed in steel beams with a significant increase in dry capacity with a change in the cross section of the upper and lower shelves, reducing material consumption and cost of construction.

Active sensor wave propagation technique is a relatively new method for in-situ nondestructive evaluation (NDE). Elastic waves propagating in material carry the information of defects. These information can be extracted by analyzing the... more

Active sensor wave propagation technique is a relatively new method for in-situ nondestructive evaluation (NDE). Elastic waves propagating in material carry the information of defects. These information can be extracted by analyzing the signals picked up by active sensors. Due to the physical property of wave propagation, large area can be interrogated by a few transducers. This simplifies the process