Characterization of spherically focused transducers using an ultrasonic measurement model approach

A new and computationally efficient method is developed for characterizing a spherically focused, ultrasonic transducer (and its accompanying test system). Procedures for determining the probe's effective radius, effective focal length, and system efficiency factor are described. Predicted responses that make use of these effective parameters are shown to correspond very well to measured responses for a number of different transducers.     

A frequency domain ultrasonic model for the pulse-echo transducer response of an arbitrary scatterer in a fluid

A very general model formulation is presented in the frequency domain for the pulse-echo ultrasonic response of an arbitrary scatterer in a fluid. The transducer is modeled as a piston source and the scatterer can be located anywhere in the transducer wavefield. The model is computationally efficient and is shown to agree well with initial experiments.     

Ultrasonic crack characterization via a constrained inversion algorithm

The Kirchhoff approximation is used to show that the time domain impulse response of an isolated flat crack can be given a simple geometrical interpretation in terms of the derivative of a projected length function. For an elliptical crack, this derivative can be obtained explicitly to yield the two edge-diffracted waves which originate from the flashpoints of the crack. An explicit coordinate invariant expression is obtained from this elliptical crack solution which relates the time difference, t, between the arrival of these edge-diffracted waves and the crack size and orientation. Previously, we have proposed that this expression, together with t measurements in different scattering directions, could be used in a regression analysis as the basis for performing a constrained inversion of crack scattering data (i.e., where we attempt to obtain the best equivalent flat elliptical crack that fits the scattering measurements). Here we will demonstrate some results of applying the proposed algorithm using noisy synthetic data. The sensitivity of the results to both, number of measurements and transducer orientation, will be discussed.     

Modeling Ultrasonic Pulse-Echo Signals from a Flat-Bottom Hole in Immersion Testing Using a Multi-Gaussian Beam

This paper proposes an ultrasonic measurement model that can predict the pulse-echo signals from a flat-bottom hole in an isotropic, homogeneous solid specimen immersed in water in a computationally efficient manner. To develop such a model, a measurement model approach is adopted based on two important assumptions: the paraxial approximation for the transducer beam and the small flaw assumption for the flat-bottom hole. The modular model that results from these two assumptions contains three terms: a diffraction correction term, a far-field scattering amplitude term and a system efficiency factor term. The diffraction correction is defined based on a multi-Gaussian beam model which allows the rapid evaluation of the wave field incident on the hole. The far-field scattering amplitude of the flat-bottom hole is obtained using the Kirchhoff approximation together with the small flaw assumption. The system efficiency factor is determined by deconvolution of an experimental front surface reflection signal by a reference reflector model. Here, the contribution of each of these three terms to the overall measurement model are described in detail and the accuracy of the proposed model is verified by the comparison of the model-based predictions to experiments.     

Modeling and Measuring All the Elements of an Ultrasonic Nondestructive Evaluation System I: Modeling Foundations

Abstract

A comprehensive model of an ultrasonic nondestructive evaluation (NDE) flaw measurement system is developed that combines models for the electrical components (pulser/receiver, cabling), electromechanical components [transducer(s)], and the acoustic/elastic processes present in the materials being inspected, including the scattering of ultrasonic waves from a flaw. This model is called the electroacoustic measurement (EAM) model. Here, in Part I, the underlying modeling foundations of the EAM model are described in detail and the use of the EAM model is demonstrated in a transducer design study. This EAM model provides a new, powerful tool for analyzing virtually any element in the measurement process. In Part II it will be shown that this power can be extended to characterizing typical commercial measurement systems through the use of models and purely electrical measurements of the system components.     

A unified constrained inversion model for ultrasonic flaw sizing

Equivalent flaw sizing using ultrasonic waves is an approach whereby shape and orientation information of a defect are obtained in terms of a best-fit simple geometry that is able to represent the major aspects of the flaw. Separate examples of this approach have previously been developed for volumetric flaws and cracks using the Born and Kirchhoff approximations, respectively. Here, these separate algorithms are unified into a single algorithm capable of sizing both volumetric flaws and cracks. Some examples of the performance of this unified algorithm on both synthetic and experimental data are also given.     

Modeling and Measuring All the Elements of an Ultrasonic Nondestructive Evaluation System II: Model-Based Measurements

In Part I: Modeling Foundations [1], a comprehensive model of an ultrasonic nondestructive evaluation (NDE) flaw measurement system was developed. Here, it will be shown that this comprehensive model can be used to completely characterize commercial measurement systems where all the elements of the system can be either modeled explicitly or measured, using purely electrical measurements. When combined, these models and measurements are shown to be able to predict accurately the measured signals in an ultrasonic test.     

Modeling Angle Beam Ultrasonic Testing Using Multi-Gaussian Beams

This paper proposes a new approach to modeling angle beam ultrasonic testing that can predict pulse-echo signals, in an absolute and computationally efficient manner, from various reflectors in steel welded joints. This approach relies on a model of the entire ultrasonic measurement process, a model which requires one to solve three subsidiary problems; 1) determination of a system efficiency factor, 2) evaluation of the ultrasonic beam field around the flaw, and 3) calculation of the scattering from the reflector. Here, solutions are offered for each of those three subsidiary problems. To solve the first problem we employ the specular reflection from the cylindrical part of a STB-A1 (Standard Test Block in compliance with Japanese Industrial Standards Z 2347) (equivalently IIW (International Institute of Welding) type 1) standard block to determine the system efficiency factor. To solve the second problem, we calculate the ultrasonic wave field at the flaw with a highly efficient multi-Gaussian beam model. For the third problem, we treat the scattering from a reflector by high frequency approximations. We explicitly give the solutions to all three of these subsidiary problems for counter bore, crack, and side-drilled hole reflectors. Experimental results that validate this approach are also given.