Development of a Quantitative Flaw Characterization Module — A Status Report

Abstract

Ultrasonic waves returning from an internal bulk flaw to a wideband transducer contain information on several characteristics of this flaw. Measurements made with waves of different mode, dominant frequency, incidence angle, beamwidth, etc. are, therefore, necessary to solve the inverse problem for flaw composition, size, and orientation in an unambiguous manner.The plan for the development of a reliable and accurate volumetric-flaw characterization module encompasses three basic elements: a transducer selection protocol, a deconvolution algorithm, and the Born as well as the Franz-Gruber (satellite pulse) models for the interaction of weakly and strongly scattering internal bulk flaws, respectively. The flaw-diameter estimates obtained by applying the Born Inversion Technique (BIT) and the Satellite-Pulse Observation Technique (SPOT), based on the above models, to the results of ultrasonic backscattering experiments are compared in this paper with the nominal effective diameters of five spherical voids in a titanium-alloy specimen tested under blind conditions.

Deconvolution by Design — an Approach to the Inverse Problem of Ultrasonic Testing

“…This is essentially the method used at the National Bureau of Standards (NBS) to calibrate transducers as receivers [1]. Another example of an inverse problem in ultrasonics is the use of the Born approximation to attempt to size defects; see for example [2,3]. In this example, essentially an approximate Green's function is assumed, it being the Green's function for a weak spherical scatterer.…”

“…Then a characterization of the flaw is attempted by using the measured voltages from the scattered field and the assumed Green's function. This procedure leads to mixed results [2].…”

Status of Implementation of the Inverse Born Sizing Algorithm

“…Gruber conducted a performance evaluation on a set of spherical voids in titanium (15). The protocol of a blind test was adopted.…”