NDE Problems Research Articles

Complex Magnetic Permeability Evaluation of Steel Fibers Using Eddy Current NDE and Inverse Problem Methods

Complex Magnetic Permeability Evaluation of Steel Fibers Using Eddy Current NDE and Inverse Problem Methods

Multilevel Kernel Degeneration–Adaptive Cross Approximation Method to Model Eddy Current NDE Problems

Multilevel Kernel Degeneration–Adaptive Cross Approximation Method to Model Eddy Current NDE Problems

Reconsidering Ampere’s Double Layer Representation for Magnetic Field, Evaluation in a NDE Dection of a zero volume crack

The paper has two different objectives. The first one is to show that Ampere’s double layer method, which is equivalent to one of the Maxwell equations, leads to the integration of a simple closed form expression, thus avoiding the need to solve complicated partial differential equations. The second aim is to study the case of a zero volume defect in a NDE problem by a perturbation method and the introduction of a double layer. The combination of these two techniques leads to a very fast solution of the problem. A practical example including

Computer Modeling Solves Practical Problems in NDE

Abstract Modeling and simulation are proving to be an effective alternative to the trial-and-error practices often used when developing and evaluating nondestructive tests for materials characterization. This article demonstrates the benefits of modeling in different cases where eddy current and ultrasonic inspection methods are employed.

The DPSM method and its application to NDE problems with interfaces modelling

This paper deals with the new results of the distributed point source method (DPSM). This method has been first developed at the SATIE lab, located at the Ecole Normale Superieure of Cachan, France. This method now allows the modelling of interactions between an incident wave and an obstacle. It can be applied in the non destructive testing area, using eddy currents or ultrasonic waves.

3-D Eddy Current Analysis With the Cell Method for NDE Problems

An algebraic formulation has been developed for the solution of three-dimensional eddy current problems, according to the cell method philosophy. This formulation is presented in the frequency domain and it is based on the circulation of magnetic vector potential along primal edges and on time-integrated electric scalar potential in primal nodes of conducting region. The formulation has been applied to solve a nondestructive evaluation problem. The flaw has been modeled as a zero-thickness defect and the superposition of effects has been applied to compute the impedance variation with respect to the flawless configuration.

Time frequency and wavelet transform applied to selected problems in ultrasonics NDE

In this paper, we contribute by the development of some signal processing in order to enhance the sensibility of flaw detection, to measure thin materials thickness and to characterize defects in nature (planar or volumetric). Features for discrimination of detected echos are extracted in time domain, spectral domain and discrete wavelet representation. Compact feature vector obtained is then classified by different methods: K nearest neighbour algorithm, statistical Bayesian algorithm and artificial neural network. Mallat decomposition algorithm is also developed in order to enhance flaw detectability. Finally, time frequency algorithms based on STFT, Wigner–Ville, Gabor transform are developed and applied to thickness measurements of materials with small thickness.

A comb transducer model for guided wave NDE

Abstract A countless number of guided wave modes at particular frequencies could be selected for a particular NDE problem, each point producing special sensitivities by way of wave structure across the thickness of the component being studied and also specific penetration powers as a result of interface and surface displacement values and subsequent energy leakage into neighboring media. The mode and frequency choice has a strong influence on NDE and flaw detection, classification and sizing potential as well as an ability to propagate guided waves over long distances, despite the presence of coatings and other surrounding media. The approach to mode and frequency selection is therefore crucial, which can ultimately be based on theoretical and/or experimental means. One aspect of a theoretical approach beyond dispersion curve analysis includes theory of elasticity computations of displacement distributions across a structure. Focus can be on achieving in-plane or out-of-plane optimal values on a surface or at a specific location inside a structure in an attempt at flaw analysis or improved penetration power. From an experimental point of view, an angle beam transducer at a specific angle can be used to achieve a particular phase velocity value. Unfortunately, the presence of a phase velocity spectrum due to a transducer source influence, size and velocity pattern, as well as the frequency spectrum itself, often limits the ability to specifically achieve the particular mode and frequency of choice. Multiple modes can be obtained. An alternate transducer choice to the angle beam transducer can be a multiple element array or comb based on various design choices of element size, spacing and pulsing schedules to produce specific modes and frequencies. The purpose of this paper is to present a model and subsequent solution to a boundary value problem that can evaluate the source influence as a function of the comb transducer design parameters. Advantages of the comb transducer, the mathematical model and analysis, and sample experimental results are all presented in the paper along with an insight into future directions.

Report on 6th Japanese-German Joint Seminar on Structural Strength and NDE Problems in Nuclear Engineering

Report on 6th Japanese-German Joint Seminar on Structural Strength and NDE Problems in Nuclear Engineering

Mathematical modelling for the practice of ultrasonic inspection

This paper deals with an advanced numerical approach applied to some problems in ultrasonic NDE. The first application concerns the calculation of the DGS-diagram for a single-probe technique. It is shown that, in comparison with a conventional scalar model, the exact consideration leads to different results. Further, the accurate process of elastic wave diffraction on flaws is considered using a boundary elements technique. It is noted that for short waves this method has a difficulty because a dimension of the corresponding matrix equation increases with defect size growth. The final part of the paper is devoted to the comparison of theoretical and experimental back-scattered diagrams for various complex flaws.

Design, develop and fabricate a prototype nondestructive inspection and monitoring system for structural cables and strands of suspension bridges, Volume 1 : Texas Research Inst., Austin, Texas (United States), PB91ndash;174078/GAR, 147pp. (May 1989)

This report describes the development of a prototype magnetic perturbation NDE system for inspecting and monitoring structural cables and strands of suspension bridges. Although this method had been applied successfully to a variety of NDE problems, including small diameter cables, the application to larger diameter cables was an extremely difficult endeavor. A limited parametric laboratory investigation was conducted using a rudimentary system consisting of a 200-lb (91 kg) electromagnet with an attached Hall probe to measure the magnetic perturbations as a simulated cable was scanned. The first specimen consisted of 370 steel rods (0.25-in. (6.4-mm) diameter by 20-ft (6.1-m) long) enclosed by a 6.0-in. (15.2-cm) I.D. by 0.28-in. (7.1-mm) wall thickness steel pipe 20-ft (6.1-m) long that supported the rods and also simulated the 0.2-in. (5.1-mm) diameter soft steel spiral protective wrap used on some main cables. Magnetic anomalies in the steel pipe obscured flaw signals except for very large flaws. After many changes in the experimental arrangement which included replacing the steel pipe with an aluminum pipe, detection of a 0.27% cross-sectional area flaw at a depth of 1.9 in. (4.8 cm) was achieved. Subsequently, a prototype Magnetic Perturbation Cable (MPC) NDE system was constructed and field demonstrations were successfully conducted on the 6.3-in. (16-cm) diameter Luling Bridge stay cables (12-15 December 1988). Approximately 420 data scans (each 100 in. (2.5 m) long) were recorded. Comprehensive analyses disclosed the possibility that grouting was so thin in several regions on top of a cable that segments of wires were moved by the magnetic attractive forces at each poleface. The MPC incorporates the high sensitivity, excellent resolution, long-term stability, etc., of the magnetic perturbation method with modern microprocessor control, digital communication, computer archival storage, digital signal analyses routines, etc., into an integrated, state-of-the-art, automated NDE system that now makes it possible to apply modern quantitative structural lifetime assurance strategies to suspension bridge cables.

Ultrasonic NDE of solid-state bonds: Inertia and friction welds

This paper discusses a number of special ultrasonic NDE problems of particular interest to inertia and friction welds, but most of the results can be readily applied to other similar or dissimilar solid-state bonds as well. One of the major problems associated with dissimilar bonds is the “blinding” effect of the strong interface reflection caused by the inherent elastic discontinuity at the otherwise flawless boundary. A novel signal-processing technique based on the symmetric part of the boundary reflections from the two opposite sides of the interface is introduced and shown to yield a quantitative measure of boundary imperfection even for very good, apparently flawless bonds. The second problem addressed in this paper is the so-called “cold-weld” effect. As a combined result of heat softening and external pressure, intimate mechanical contact can be achieved without real fusion. Frequency analysis of the reflected ultrasonic signal from such cold-welded areas is shown to be capable of measuring the degree of plastic deformation at the contacting surfaces and, indirectly, to assess interface pressure and temperature. The third problem considered in this paper is the ultrasonic evaluation of the characteristic layered distribution of the grain structure in flawless inertia and friction welds. As an example, the thickness of the heat-affected zone (HAZ) was determined by ultrasonic spectroscopy, and the results were found to be in good agreement with independent optical profile measurements. Furthermore, the HAZ thickness is shown to be strongly correlated to welding pressure, therefore it offers a sensitive indicator for bond quality assessment as well.

Stationary formulas for computing the response in eddy-current NDE

Stationary or variational formulations have been proven to be useful in a number of electromagnetic problems. This paper presents such a formulation for the response in the eddy-current NDE problem. It thus provides an approach to estimating the response due to arbitrary defects in cases where a reasonable “first guess” for the current distribution responsible for the scattered fields can be obtained.

Ill-posed and well-posed problems in inverse elastodynamic scattering for nondestructive evaluation

The practical significance of ill-posedness in a data reduction problem is reviewed. Inverse elastodynamic scattering is shown to be ill-posed in general, although suitably restricted problems may be well-posed. These results underscore the need to analyze carefully the errors of data reduction problems in NDE, and to focus attention on final results of an NDE exercise, rather than on intermediate steps.