Flaw Reconstruction Research Articles

Apparatus and technique for reconstruction of flaws using model-based elastic wave inverse ultrasonic scattering

An automated multiviewing ultrasonic apparatus and signal processing routine have been developed for utilization in nondestructive evaluation (NDE) of materials. The instrument has been developed to take advantage of recent advances in long and intermediate wavelength inverse scattering of elastic waves, and provides a 3-D reconstruction of a flaw. Although the reconstruction obtained does not contain fine details of the flaw’s structure, it provides sufficient information about the flaw (size, orientation, and selected materials properties) so that failure-predictive decisions can be made.

Products of research and development in NDT

The Nondestructive Ultrasonic Testing and Evaluation is directed to describe flaws microstructure, structure residual stress, reliability or quality insurance. An overview is given on the scientific background, interpretation capability based upon mathematic-numerical models, new design of equipments and demonstrated at components containing relevant flaws. Emphasis is laid upon SNR-improvement in the UT of austenitic weldings. Examples are shown using the backscattering technique with linear polarized shear waves. Stress measurements are performed with electromagnetic ultrasonic probes (EMAT). The surface inspection with magnetic imaging of the eddy current field or the multi-frequency eddy current methods are described. The possibilities of detection, classification and reconstruction of flaws are demonstrated in the time- and frequency domain with the satellite pulse echo technique, focal probes and the synthetic aperture methods like ALOK, Phased Array, Holography and SAFT.

Quantitative characterization of flaws near a surface using inverse born approximation

Quantitative reconstruction of volumetric flaws near a surface of an elastic solid has been carried out experimentally by analyzing the scattered ultrasonic waves. The inverse Born approximation (developed for flaws in bulk materials) was tested for the first time in the determination of the size, shape, and orientation of near-surface flaws. We have studied spherical solid inclusions at various depths below the surface. In addition we examined an approximately 2:1 prolate spheroidal inclusion which was located one major axis below the surface. The determination of the flaw's size, shape, and orientation in terms of an equivalent ellipsoid is realized by performing nonlinear least-squares iteration of the one-dimensional Born inversion results obtained at various scattering directions within a finite aperture. The reconstruction is in good agreement with the actual parameters of the flaw.

Geometric reconstruction of flaws by one‐dimensional inverse Born approximation

We report a three‐dimensional reconstruction of the size, shape, and orientation of volumetric flaws (inclusions and voids) based on the results of one‐dimensional Born inversions of the scattering amplitudes for observation directions confined to a finite angular aperture. The reconstruction is realized by performing nonlinear least squares iteration of the Born inversion results in terms of an equivalent ellipsoid. We have successfully reconstructed spherical and nonspherical inclusions in the bulk of plastic samples and an oblate spheroidal void in a titanium disk. In addition we have applied the ellipsoidal reconstruction method to a spheroidlike inclusion very near the surface of a sample and obtained good results. The method was found to remain quite successful even with experimental data confined to a rather limited aperture. Effects on the one‐dimensional inverse Born algorithm due to characteristic resonances of the inclusions and flaw‐surface interactions will be discussed. [Work sponsored by En...

Non-Destructive Testing of Materials

This text reviews the current state of all types of electromagnetic testing techniques and considers the implications of innovations for future inspection practice. Topics covered include: inversion; imaging and flaw reconstruction; advanced signal processing; artificial intelligence and neural networks; modelling; simulation and benchmark problems; reliability of inspections; new techniques and novel sensors; and automation of data acquisition and processing.