Location

La Jolla, CA

Start Date

1-1-1987 12:00 AM

Description

To exploit theoretical advances in elastic wave inverse scattering, an automated multiviewing ultrasonic transducer system and the associated signal processing algorithms have been developed at the Ames Laboratory for the reconstruction of the size, shape, and orientation of volumetric flaws [1]. The flaw sizing algorithm is based on elastic wave inverse scattering theories in the long and intermediate wavelength, regime [2,3] and the three-dimensional reconstruction algorithm finds the equivalent ellipsoid that best fits the flaw sizes in the various viewing directions [4,5]. The original multiprobe system consists of six peripheral transducers equally spaced in a circle surrounding one transducer at the center. The peripheral transducers may be tilted at an angle toward the center to increase the aperture and can also be translated along their respective axes to allow an equilization of the acoustic propagation time. The axis of the aperture cone is normally placed perpendicular to the part surface. The flaw sizing procedure was a one-dimensional inverse Born algorithm to determine the flaw’s centroid-to-tangent plane distances for a number (normally 13 or 19) of pulse-echo or pitch-catch scattering directions within a finite aperture cone. The flaw sizes are then used as inputs to a nonlinear least squares regression program to yield a complete geometric reconstruction in the form of three semi-axes and three Euler angles of the best-fit ellipsoid. Using this system, successful reconstructions have been obtained for both oblate spheroidal (disk-like) and prolate spheroidal (rod-like) inclusions and voids. The readers are referred to a complete description of the system in Ref. 1.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

6A

Chapter

Chapter 2: Imaging, Microscopy, Inversion and Reconstruction

Section

Inversion and Reconstruction

Pages

585-594

DOI

10.1007/978-1-4613-1893-4_66

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Characterization of Flaw Shape and Orientation Using Ultrasonic Angular Scans

La Jolla, CA

To exploit theoretical advances in elastic wave inverse scattering, an automated multiviewing ultrasonic transducer system and the associated signal processing algorithms have been developed at the Ames Laboratory for the reconstruction of the size, shape, and orientation of volumetric flaws [1]. The flaw sizing algorithm is based on elastic wave inverse scattering theories in the long and intermediate wavelength, regime [2,3] and the three-dimensional reconstruction algorithm finds the equivalent ellipsoid that best fits the flaw sizes in the various viewing directions [4,5]. The original multiprobe system consists of six peripheral transducers equally spaced in a circle surrounding one transducer at the center. The peripheral transducers may be tilted at an angle toward the center to increase the aperture and can also be translated along their respective axes to allow an equilization of the acoustic propagation time. The axis of the aperture cone is normally placed perpendicular to the part surface. The flaw sizing procedure was a one-dimensional inverse Born algorithm to determine the flaw’s centroid-to-tangent plane distances for a number (normally 13 or 19) of pulse-echo or pitch-catch scattering directions within a finite aperture cone. The flaw sizes are then used as inputs to a nonlinear least squares regression program to yield a complete geometric reconstruction in the form of three semi-axes and three Euler angles of the best-fit ellipsoid. Using this system, successful reconstructions have been obtained for both oblate spheroidal (disk-like) and prolate spheroidal (rod-like) inclusions and voids. The readers are referred to a complete description of the system in Ref. 1.