A Three-Dimensional Boundary Element Model for Eddy Current NDE

The long-range objective of the work reported here is to provide a theoretical basis for the prediction of the probability of flaw detection in eddy current nondestructive evaluation (NDE). As demonstrated in a previous communication [1], much of the labor involved in probability of detection analyses can be transferred to a computer if one has available a reliable algorithm for the prediction of flaw signals as a function of flaw size and shape, probe geometry, and the other parameters defining an eddy current inspection. Because there is no simplifying symmetry in the interaction of a general eddy current field with a flaw of arbitrary shape and position, the model used for flaw signal predictions must be three dimensional, and capable of predicting the probe impedance change for a flaw at an arbitrary position in the field of an eddy current probe. The immediate objective of the present work is to develop such a three-dimensional model

Theory of Eddy Currents in Metal Matrix Composites

Eddy current nondestructive characterization of composite materials is complicated by the anisotropic nature of their electrical conductivities. Earlier calculations for anisotropic materials show that eddy current distributions can be quite different from the rather simple patterns produced in isotropic media, and this can have a profound effect on probe response [1-3]. It follows that proper interpretation of eddy current data in terms of microstructural material properties requires understanding of how microstructure affects electrical anisotropy and how this anisotropy is reflected in the response of an eddy current probe

Deformation mechanics of deep surface flaw cracks

A combined analytical and experimental program was conducted to determine the deformation characteristics of deep surface cracks in Mode I loading. An approximate plane finite element analysis was performed to make a parameter study on the influence of crack depth, crack geometry, and stress level on plastic zones, crack opening displacement, and back surface dimpling in Fe-3Si steel and 2219-T87 aluminum. Surface replication and profiling techniques were used to examine back surface dimple configurations in 2219-T87 aluminum. Interferometry and holography were used to evaluate the potential of various optical techniques to detect small surface dimples on large surface areas

Calculation of Eddy Current Fields for Coils of Arbitrary Shape

In the design of an eddy current inspection device, it is useful to have available a means of visualizing the eddy current distribution produced in the material to be tested. This is evidenced by the widespread use of the early models of Dodd and Deeds [1], who provided analytic solutions for the field in a number of axisymmetric probe geometries. The analytic approach was later extended [2–4] to include a more general class of coils, and was applied to the case of a circular, air-core horizontal coil [4]

Electric Current Perturbation Calculations for Half-Penny Cracks

The electric current perturbation (ECP) method1–4 consists of inducing or injecting an electric current flow in the material to be examined and then detecting localized perturbations of the magnetic flux associated with current flow around material defects such as cracks or inclusions. Empirically, ECP data has shown strong correlations among certain signal features and crack size characteristics, and thus promises to be a useful method for quantitative NDE. To aid in the further development of the method, the objectives of the work reported in this paper are (1) to develop a mathematical model of the ECP flux distribution for a half-penny crack, (2) to determine the degree of validity of the model through comparisons with experimental data, and (3) to develop a detailed theory of sizing relationships for half-penny cracks

Eddy Current measurement of Fiber Volume Fraction in Metal Matrix Composite Extrusions

The objective of this work was to develop an eddy current method for measuring fiber volume fraction in continuous-fiber metal matrix composites. Because an eddy current measurement can be affected by the spatial distribution of fibers as well as the overall fiber density, the measurement method had to be tolerant of possible variations in spatial distribution that might be encountered in practice. For this reason, the work began with the development of models of the effective resistivity tensor for a composite with an arbitrary fiber distribution and the resulting eddy current probe response [1,2]. The intent was to use these models to help design a measurement method and to test the method for ordered and disordered arrangements of fibers

Eddy Current Detection of Subsurface Cracks in Engine Disk Boltholes

The development of a reliable eddy current inspection system to detect second layer cracks in sleeved engine disk bolt holes poses serious difficulties. This paper discusses some initial results obtained in two separate investigations that are aimed at advancing the state-of-the-art in eddy current detection of subsurface cracks. Both finite element design optimization results of a horseshoe shaped ferrite core probe, and the results of preliminary evaluation of the applicability of electric current perturbation (ECP) technique to the current problem are presented in this paper

Eddy current probe design for second-layer cracks under installed fasteners

The United States Air Force has an operational need to reliably detect second-layer cracks around fastener holes in two-layer airframe structures with the fasteners in place. Because access to the second layer is usually not available, the inspection must be performed by placing a probe on the outer surface of the structure and detecting cracks through the first layer. Eddy current methods have been applied to this inspection problem [1–6], and have met with some success; however, much improvement is still needed to achieve the desired sensitivity to cracks and rejection of signals caused by the geometry of the structure under inspection

AN Ultrasonic Ray-Trance Code for Complex Geometry Applications

Many applications of ultrasonic testing (UT) are made difficult by the complex geometrical shape of the part to be inspected. A simple ray-trace analysis of the geometry may suffice to determine transducer positions and beam angles to provide adequate coverage of the region to be interrogated. In addition, however, the analyst must have estimates of backscattered amplitudes to determine if flaw signals are measurable. Thus, a combination of complex-geometry ray tracing with calculations of flaw-scattering amplitudes is required for the design and optimization of UT procedures

The Somatosensory Link in Fibromyalgia: Functional Connectivity of the Primary Somatosensory Cortex Is Altered by Sustained Pain and Is Associated With Clinical/Autonomic Dysfunction

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111091/1/art39043.pd