Location

Williamsburg, VA

Start Date

1-1-1986 12:00 AM

Description

Obtaining flaw geometry and orientation information from ultrasonic measurements often involves time consuming scanning and data processing functions. One possible way of reducing the amount of information needed for flaw characterization purposes is to require that the fine details of the flaw not be resolved but instead to obtain the best “equivalent” flaw geometry and orientation that fits a predefined simple flaw shape of unknown size and orientation. Hsu et al. [1] have implemented such a procedure for isolated voids and inclusions by using the Born approximation and obtaining a non-linear least squares estimation of the best ellipsoid that fits the data. Here, we will demonstrate that a similar constrained inversion procedure can be developed using the Kirchhoff approximation [2-4] for a flat elliptical crack. Using the results of our previous paper [5], an explicit coordinate-invariant expression that relates the time difference, At, between the arrival of the waves diffracted from the flashpoints of the crack and the crack shape and orientation is obtained. This expression, together with At measurements in different scattering directions is placed into a regression analysis to obtain a set of equivalent flat elliptical crack parameters. A series of tests of this method using noisy synthetic data are considered and the sensitivity of the results to number of measurements and the viewing aperture of the transducer set-up is discussed.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

5A

Chapter

Chapter 2: Inversion, Imaging and Reconstruction

Section

Inversion

Pages

367-374

DOI

10.1007/978-1-4615-7763-8_37

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Ultrasonic Crack Characterization: A Constrained Inversion Algorithm

Williamsburg, VA

Obtaining flaw geometry and orientation information from ultrasonic measurements often involves time consuming scanning and data processing functions. One possible way of reducing the amount of information needed for flaw characterization purposes is to require that the fine details of the flaw not be resolved but instead to obtain the best “equivalent” flaw geometry and orientation that fits a predefined simple flaw shape of unknown size and orientation. Hsu et al. [1] have implemented such a procedure for isolated voids and inclusions by using the Born approximation and obtaining a non-linear least squares estimation of the best ellipsoid that fits the data. Here, we will demonstrate that a similar constrained inversion procedure can be developed using the Kirchhoff approximation [2-4] for a flat elliptical crack. Using the results of our previous paper [5], an explicit coordinate-invariant expression that relates the time difference, At, between the arrival of the waves diffracted from the flashpoints of the crack and the crack shape and orientation is obtained. This expression, together with At measurements in different scattering directions is placed into a regression analysis to obtain a set of equivalent flat elliptical crack parameters. A series of tests of this method using noisy synthetic data are considered and the sensitivity of the results to number of measurements and the viewing aperture of the transducer set-up is discussed.