摘要:

Ultrasonic wave scattering at interface of a cylindrical solder embedded in an aluminum block is analyzed by finite element method under plane strain. For nondestructive characterization of inclusion, the analysis of ultrasonic wave scattering at heterogeneous, anisotropic and irregular shaped inclusions is necessary. Theoretical analysis is limited for only idealized geometry and material properties, therefore only numerical analysis is applicable for inclusions of irregular shape and real material properties. As a first step, FEM analysis is applied for an aluminum block with an inclusion of cylindrical solder. Longitudinal short pulse is given over a width larger than the diameter of the cylinder on one face of the aluminum block perpendicular to the axis of the cylinder. The refracted longitudinal wave at aluminum/solder interface is focused within the solder, and this wave partially reflected at another solder/aluminum boundary. The amplitude of the reflected wave is comparable to those reflected at the aluminum/solder interface. The shear wave which have excited by mode change at the aluminum/solder interface are backscattered in the directions of +.50 degree and superposed incoming shear wave. The numerical results are close to the surface wave propagation measured by laser ultrasonic method. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306039

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Since wave speeds in anisotropic materials depend on the direction of propagation, the characteristics of scattering and propagation of elastic waves are different from those in isotropic materials. It is therefore necessary to solve scattering problems of elastic waves to establish a quantitative ultrasonic nondestructive method for anisotropic materials. In this study, a time domain boundary element method is developed with use of fundamental solutions for a general anisotropic solid obtained by Wang and Achenbach [Geophysical J. Int., Vol. 118, pp. 384–392, 1994]. The boundary element method is applied to scattering problems of elastic waves by various defects such as a cavity and an inclusion in an infinite anisotropic solid. It is shown that the amplitudes and phases of backscattered waves are quite different from those in isotropic materials and the scattering characteristics are very important factors in the nondestructive ultrasonic evaluation of anisotropic materials. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306040

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We report the development of new techniques for modeling pulse-echo scattering using a water-coupled transducer, and their success in accurately predicting both the size and shape of the echoes from small solid defects. Our new methods use separate grids to model the solid and the liquid, and these are only related along the interface using pseudonode formulations based on the boundary conditions. The twin grid formulation does not have any problems with discontinuities along the interface. It has also been shown to have excellent stability properties. When we compare our finite difference predictions with experimental data from known defects, we take care to subtract measurements made without the defect (with all else unchanged) from the measurements with the defect, in order to avoid spurious interface echoes. We do this for both the experimental and the finite-difference “data.” The finite difference predictions match the experimental measurements to high accuracy. Having validated the finite difference techniques, we can use them to monitor and visualize the various scattered and reflected waves, giving valuable insights into their physical origins. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306041

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

An integral equation is formulated for the scattering problem by the planar periodic array of scatterers. In this case, the fundamental solution is in a form of double series and the series may converge very slowly in a certain configuration of periodic scatterers. In this paper, a practical numerical integration based on Ewald method is investigated for the fundamental solution with the double infinite series. In more detail, the fundamental solution is converted into the integral form with rapidly convergent integrand and the Gauss’ numerical integration is performed here to evaluate the integral. The convergence and the efficiency of the method are demonstrated numerically for the integral equation by the planar array of scatterers. The reflection and transmission coefficients are calculated as an application of the present numerical evaluation for the fundamental solution. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306042

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The influence of particle mass density on the reflection and transmission spectra of a plane longitudinal wave normally incident on a periodic (square) array of identical spherical particles in a polyester matrix are measured at wavelengths which are comparable to the particle radius and the inter-particle distance. The spectra are characterized by several resonances whose frequencies are close to the cut-off frequencies for the shear wave modes, which are analogs of spectral orders in diffraction gratings. Arrays of heavy particles (lead and steel) exhibit a pronounced resonance anomaly which occurs when the lattice resonant frequency is close to the frequency of the rigid body translation (dipole) resonance of an isolated sphere in an unbounded matrix. An approximate low frequency theory is developed which takes into account the multiple scattering effect. The theory shows good comparison with the experimental data for arrays with particle area fractions as high as 32&percent;. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306043

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

It may be shown formally that one possible approach to evaluating the dynamic response of a multi-ply fiber composite plate to an impulsive point load is by integrating the response to a line load over all orientations of the load line. This is a computationally intensive exercise and as a preliminary step, it is instructive to consider the simpler generic problem of the dynamic response of a two-dimensional elastic medium to a point load. For a two-dimensional isotropic material, integration of the line load solutions may be performed analytically and leads, as is well known, to the Bessel function solution. For an isotropic material, analytic integration is not possible and it is necessary to carry out the integration numerically. The paper will report the results of the numerical integration for both the isotropic and anisotropic media, showing some of the contributions at a fixed location arising from the individual line loads. For any orientation of the line load, the contribution to the overall response is non-causal but complete integration leads to a properly casual solution. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306044

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In nondestructive testing the evaluation of austenitic steel welds with ultrasound is a commonly used method. But, since the wave propagation, scattering, and diffraction effects in such complicated media are hardly understood, computer simulations are very helpful to increase the knowledge of the physical phenomena in such samples. A particularly powerful numerical time domain modeling tool is the well established Elastodynamic Finite Integration Technique (EFIT). Recently, EFIT has been extended to simulate elastic waves in inhomogeneous anisotropic media. In this paper, the step-by-step evaluation of ultrasonic wave propagation in inhomogeneous anisotropic media will be described and the results will be validated against measurements. As a simplified model, a V-butt weld with perpendicular grain structure is investigated. The coincidence between the B Scans of the simulation and the measurement of an idealized V-butt weld is remarkable and even effects predicted by theory and simulation—the appearance of two coupled quasi-SV waves—can be observed. As a next step, an improved and more realistic model of the grain orientation inside the V-butt weld is introduced. This model has been implemented in the EFIT code and has been validated against measurements. For this verification, measured and simulated B-Scans for a real-life V-butt weld have been compared and a significant coincidence has been observed. Furthermore, the main pulses in the B-Scans are interpreted by analyzing the snapshot-movies of the wavefronts. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306045

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Electricite´ de France conducts a study on the effects of metallurgical structures of austenitic stainless steel welds on ultrasonic wave propagation for application to ultrasonic nondestructive testing. Two complementary methods are performed: a direct experimental study on various kinds of welds and a theoretical study using ultrasonic simulation tools. This simulation study makes use of two different models. The first, called ULTSON-2D, is a finite element code developed by the EDF Research and Development Division. It is adapted to orthotropic media and heterogeneous structures and takes into account the scattering of waves from flaws such as cracks and holes. The second, called Champ-Sons is a 3D semi-analytical code developed by the French Atomic Energy Commission (CEA) which allows to predict ultrasonic beam radiation into anisotropic and heterogeneous media. Both models deal with broadband excitation pulses since they are time-dependent. The present study aims at evaluating the ability of the two models to predict typical beam distortion effects in complex anisotropic and heterogeneous weld structures as compared to experimental measurements. This study is based on preliminary results of weld structural characterization presented in a companion paper. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306046

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The theory of plane wave propagation in layered structures has been applied in the formulation of Nayfeh in order to calculate scattering coefficients due to reflection and transmission at the grain boundaries in austenitic weld metal and cast material. Each layer is assumed to be a cubic homogeneous mono-crystal. Lower symmetries of the layer down to the triclinic case may also be assumed, e.g., transverse isotropy of the columnar grained texture in austenitic weld metal. The layers are rigidly bonded and the multi-layer package embedded in water or between solid substrates. Scattering coefficients are calculated by a transfer matrix approach. Ultrasonic properties of the single layers are algebraically linked together resulting in a simple operator for calculation of reflection and transmission coefficients at the multi-layer package boundaries. Critical angle phenomena may cause failure of solution and are limiting the range of application of the transfer matrix approach, as they cause the matrix numerical condition to decrease down to singularity. This is handled by using complex algebra. The transfer matrix method has been applied to multi-layer packages immersed in water. In case of solid substrates of the multi-layer package transmission is occurring at a larger range of incidence angles. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306047

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The elastic field of a time-harmonic point source acting in a transversely isotropic, homogeneous, linearly elastic solid is studied. First, the representation of the Green’s tensor as an integral over the unit sphere is obtained. It consists of three waves: quasi-longitudinal (P), shear-horizontal (SH) and quasi-shear (SV). Then, an original exact analytical solution for the SH wave in terms of elementary functions is derived. The complete far-field asymptotic approximation of P and SV waves is obtained next, using the uniform stationary phase method. For the P wave it involves the leading term of the ray series since there is only one arrival of this wave. The wave surface for the SV wave contains conical points and cuspidal edges. The asymptotic description applicable near these singular directions is derived involving the Airy and Bessel functions. The directions close to the points of tangential contact of the SH and SV sheets of the wave surface are also treated. Numerical results in both frequency and time domain are presented. They show that the agreement between the outputs of the asymptotic and direct numerical codes is very good throughout all regions but the former can be orders of magnitude faster. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306048

出版商:AIP    

年代:1900

数据来源: AIP