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Ultrasonic Beam Propagation in Highly Anisotropic Materials Simulated by Multi-Gaussian Beams
Hyunjo Jeong,Lester W. Schmerr,Jr 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.8
The necessity of nondestructively inspecting fiber-reinforced composites, austenitic steels, and other inherently anisotropic materials has stimulated considerable interest in developing beam models for anisotropic media. The properties of slowness surface play a key role in the beam models based on the paraxial approximation. In this paper, we apply a modular multi-Gaussian beam (MMGB) model to study the effects of material anisotropy on ultrasonic beam profile. It is shown that the anisotropic effects of beam skew and excess beam divergence enter into the MMGB model through parameters defining the slope and curvature of the slowness surface. The overall beam profile is found when the quasilongitudinal (qL) beam propagates in the symmetry plane of a transversely isotropic gr/ep composite. Simulation results are presented to illustrate the effects of these parameters on ultrasonic beam diffraction and beam skew. The MMGB calculations are also checked by comparing the anisotropy factor and beam skew angle with other analytical solutions.
Complete Modeling of an Ultrasonic NDE Measurement System : An Electroacoustic Measurement Model
Dang, Chang-jiu,Schmerr Jr., W. Lester 한국비파괴검사학회 2001 한국비파괴검사학회지 Vol.21 No.1
It will be shown how models can simulate all the elements of an ultrasonic NDE measurement system, including the pulser/receiver, cabling, transducer(s), and the acoustic/elastic waves fields. When combined, these models form what is called the electroacoustic measurement model. It will be demonstrated how this electroacoustic measurement model can be used to conduct parametric transducer and system studies and how the model can form the basis for experimentally characterizing all the elements of the ultrasonic measurement system using purely electrical measurements.
Effects of Material Anisotropy on Ultrasonic Beam Propagation: Diffraction and Beam Skew
Jeong, Hyun-Jo,Schmerr, W. The Korean Society for Nondestructive Testing 2006 한국비파괴검사학회지 Vol.26 No.3
The necessity of nondestructively inspecting austenitic steels, fiber-reinforced composites, and other inherently anisotropic materials has stimulated considerable interest in developing beam models for anisotropic media. The properties of slowness surface playa key role in the beam models based on the paraxial approximation. In this paper, we apply a modular multi-Gaussian beam (MMGB) model to study the effects of material anisotropy on ultrasonic beam profile. It is shown that the anisotropic effects of beam skew and excess beam divergence enter into the MMGB model through parameters defining the slope and curvature of the slowness surface. The overall beam profile is found when the quasilongitudinal(qL) beam propagates in the symmetry plane of transversely isotropic austenitic steels. Simulation results are presented to illustrate the effects of these parameters on ultrasonic beam diffraction and beam skew. The MMGB calculations are also checked by comparing the anisotropy factor and beam skew angle with other analytical solutions.
SH 파의 균열 산란장 해석 : 근사혜와 엄밀혜의 비교 Comparisons of Approximate and Exact Solutions
정현조,박문철,송성진,Schmerr, Jr., L. W 한국비파괴검사학회 2004 한국비파괴검사학회지 Vol.24 No.4
SH파의 균열 산란장 해석을 위하여 먼저 균열개구변위(COD)를 미지수로 하는 경제적분방정식(BIE)을 수립하였다. 폭 2a의 고립된 2차원 균열(slit)에 임의의 각도로 입사하는 시간조화 평면파에 대하여 COD를 주파수 ka의 함수로 구하였으며, 다른 연구 결과와 잘 일치함을 확인하였다. 초음파 비파괴평가에서 중요한 변수로 취급되는 원거리 산란음장을 두 가지 방법으로 구하였다. 펄스-에코 모드에서 Kirchhoff 근사법과 BIE-COD에 기초한 엄밀해의 결과를 입사각도와 주파수의 함수로 계산하고 서로 비교하였다. SH파가 균열면에 수직으로 입사/반사한 경우 산란음장은 최대가 되고, 두 방법은 정확히 일치하였다. 수직입사에서 멀어질수록 산란진폭은 모두 급격히 감소하며, Kirchhoff 근사법은 엄밀해와 차이를 보였다. 시간 영역의 원거리 산란진폭 거동을 구하기 위하여 대역폭을 갖는 중심주파수 10MHz를 곱하고, 퓨리에 역변환으로 시간영역 신호를 계산하였다. 경사 입사시에 시간영역의 진폭은 좌우 균열 선단에 의해 분리되며, 두 신호 사이의 시간 간격은 균열의 크기와 관련된다. 엄밀해와 비교할 때 Kirchhoff 근사법은 정확한 시간 간격을 제공하나, 동일한 크기의 균열 선단 신호를 제공하는 부정확함이 있다. This paper describes a crack scattering model for SH wave based on the boundary integral equation (BIE) method, where the fundamental unknown is crack opening displacement (COD). When a time harmonic plane wave was incident on a 2-D isolated crack (slit) of width 2a, the COD distributions were numerically calculated as a function of ka. The calculated COD agreed well with results obtained with other methods. The far-field scattering amplitude, which completely characterizes the flaw response, was calculated in two ways. The Kirchhoff approximation and the BIE-COD exact formulation were compared in terms of incidence angle and frequency ka in a pulse-echo mode. Maximum response was obtained for both methods at the specular reflection direction. Away from the specular direction, the Kirchhoff approximation becomes less accurate. The time domain crack response was also calculated using a band-limited spectrum of center frequency 10MHz. At oblique incidence to the crack both methods show the existence of an antisymmetric flash points occurring from the crack edge. The Kirchhoff approximation provides an exact time interval between flash points, although it unrealistically gives the same amplitude.
Transferring Distance-Amplitude Correction Curves : A Model-based Approach
Kim, Hak-Joon,Schmerr Jr., Lester W.,Song, Sung-Jin,Sedov, Alexander 한국비파괴검사학회 2003 한국비파괴검사학회지 Vol.23 No.6
In practice, it is common to manufacture reference blocks containing simple reflectors to obtain distance-amplitude correction (DAC) curves. However, the construction of DAC curves in this manner requires the use of a large number of specimens with appropriate curvatures and reference reflectors located at various depths. Therefore, less costly and quantitative procedures are strongly needed. To address such a need, in this study, we have developed model-based transfer curves to relate a DAC curve obtained in a particular reference configuration with that for a completely different configuration. An example of transferring DAC curves, using the proposed transfer curves, is given.
Transferring Distance-Amplitude Correction Curves - A Model-based Approach
김학준,Lester W. Schmerr Jr,송성진,Alexander Sedov 한국비파괴검사학회 2003 한국비파괴검사학회지 Vol.23 No.6
In practice, it is common to manufacture reference blocks containing simple reflectors to obtain distance-amplitude correction (DAC) curves. However, the construction of DAC curves in this manner requires the use of a large number of specimens with appropriate curvatures and reference reflectors located at various depths. Therefore, less costly and quantitative procedures are strongly needed. To address such a need, in this study, we have developed model-based transfer curves to relate a DAC curve obtained in a particular reference configuration with that for a completely different configuration. An example of transferring DAC curves, using the proposed transfer curves, is given.
Jeong, Hyun-Jo,Park, Moon-Cheol,Schmerr Lester W. The Korean Society for Nondestructive Testing 2005 한국비파괴검사학회지 Vol.25 No.3
A modular Gaussian beam model is developed to simulate some ultrasonic testing configurations where multiple interfaces are involved. A general formulation is given in a modular matrix form to represent the Gaussian beam propagation with multiple interfaces. The ultrasonic transducer fields are modeled by a multi-Gaussian beam model which is formed by superposing 10 single Gaussian beams. The proposed model, referred to as "MMGB" (modular multi-Gaussian beam) model, is then applied to a typical contact and angle beam testing configuration to predict the output signal reflected from the corner of a vertical crack. The resulting expressions given in a modular matrix form are implemented in a personal computer using the MATLAB program. Simulation results are presented and compared with available experimental results.