An Expert System for Ultrasonic Materials Characterization and NDE

Science, engineering, and manufacturing all depend on accurate measurements. These measurements can be made either by a human or by an automated system. In both NDE and materials characterization, there are numerous evaluations and decisions which must be made based on the experience and judgment of an operator or engineer. Current automated systems are not capable of making these judgments. Instead, typically, the operator or engineer evaluates the results after the measurements have been made. Expert systems provide a method for building the expertise of the human into the measurement apparatus, thereby causing all decisions made during the measurement process to be made with the skill of expert operators

Nondestructive Detection of Voids by a High Frequency Technique

A direct solution of the ultrasonic inverse scattering problem, known by the acronym POFFIS, which stands for Physical Optics Far Field lnverse Scattering, has been developed. This technique has been used to reconstruct the shape and size of both simulated and real void flaws in materials

Dependence of the Accuracy of the Born Inversion on Noise and Bandwidth

The Born Inversions are a set of techniques for reconstructing the shape of a flaw based on the scattering of ultrasound from the flaw. One technique is the one-dimensional Born Inversion, which estimates the radius of a flaw in one direction based on one pulse-echo (i.e., backscattering) measurement in that direction. The robustness of this technique with respect to limitations on the available bandwidth and with respect to the presence of noise in the data have been investigated. The Born Inversion requires a bandwidth sufficient to include at least the range 0.5 \u3c ka \u3c 2 to give accurate estimates. The estimates continue to be accurate even when the amount of noise energy is comparable to the amount of flaw signal energy in the measurement

Measurements of Ultrasonic Scattering from Bulk Flaws of Complex Shape

The report summarizes the design and early results of scattering experiments on fl aw.s of complex shape. In close collaboration with the varied theoretical groups representing different inversion algorithms, a unique set of diffusion bonded samples have been designed. These samples contain a variety of irregular and multiple flaws whose scattering characteristics will be obtained in order to guide and evaluate developments of theoretical approaches and test specific theoretical predictions. The majority of these samples have been received an.d the measurements have begun. Results on selected samples are presented an.d compared with scattering from ellipsoidal voids. The measurements will include angular, frequency and time domain variations of the scattered signals made possible with a new ultrasonic data acquisition system

Low Frequency Characterization of Flaws in Ceramics

There is an increasing need for the characterization of small flaws in ceramic components. This project is concerned with detecting and characterizing flaws in the bulk of ceramic parts. Cylindrical tensile test specimens of hot pressed Si3N4 are being prepared and, when available, will be inspected. In preparation for the arrival of the samples, measurement techniques have been developed for inspection of cylindrical shaped samples, signal processing techniques have been developed for obtaining flaw scattering data over a broad range of frequencies and analysis techniques have been developed to automatically extract flaw characteristics from measured data

Long Wave Ultrasonic Characterization of Inclusions in Silicon Nitride

The size and material content of Fe and Si inclusions in Si3N4 have been measured by means of pulse-echo scattering of elastic waves in the frequency range 5 to 100 MHz. The inclusions were of 100 μm and 400 μm nominal diameters and were located 3 mm deep in the Si3N4. The electronic noise was reduced by signal averaging and, in some cases, the noise due to grain scattering was reduced by averaging over transducer position. The scattering amplitude A(ω) and the impulse function R(t) were obtained by a desensitized deconvolution of the reference waveform obtained by reflecting the transmitted pulse from the back surface of the sample in a defect-free region. Comparison of theory and experiment are given for A(ω) and estimates of flaw size and material content are presented

An EMAT System for Detecting Flaws in Steam Generator Tubes

The detection of flaws in steam generator tubing is often made difficult by environmental considerations. The small diameter, 7/8 inch (2.2 cm), long, 70 feet (21.3m), tubes occur in large bundles with access only being possible from the inside of the end of each tube. Furthermore, inspection must be fully automatic when the steam generator is part of a nuclear power plant because of radiation exposure limits. Consequently, a couplant free probe which can be operated remotely at the end of an automatic probe puller is needed. This paper SUillllarizes the development of an EMAT systan for this application. The device uses periodic permanent magnet probes to excite the fundamental torsional mode traveling along the axis of the tube. Included is a discussion of data obtained during a recently completed feasibility study and a description of a prototype system presently under construction

Testing the Inverse Born Procedure for Spheroidal Voids

Previously we have shown that the inverse Born approximation allows an accurate determination of the radius of spherical flaws in Ti. Here we report the results of extending that analysis to spheroidal voids. Both oblate and prolate spheroids are considered. Using scattering amplitude generated by the T-matrix method, we find that both the major and minor axes of 2-1 spheroids are accurately determined. Inversion results using experimental data will be presented for the 2-1 oblate spheroid: a comparison of the experimental and theoretical results will be given