China
Africa
Explore chapters and articles related to this topic
Robotic Electromagnetic Eddy Current Testing Technique
Published in Chunguang Xu, Robotic Nondestructive Testing Technology, 2022
Flaw detection is the main application of eddy current testing technique. It can be used to detect the defects on the surface or subsurface of conductive materials [5–9]. The operating principle of eddy current testing is electromagnetic induction. Therefore, when the material, shape, size and other factors of the specimen are changing, the induced magnetic field and the eddy current distribution will change to generate the corresponding eddy current signals. The frequency range commonly used in eddy current flaw detection is about tens of Hz to 10 MHz. Before detection, an appropriate eddy current probe should be selected according to the component material, the defect location and type, the detection sensitivity and other conditions. While meeting the detection requirements, a higher detection frequency should be considered to achieve better detection sensitivity. For example, a probe up to several megahertz can be selected to detect the surface cracks. Electrical conductivity and magnetic conductivity are two important factors affecting the penetration depth and distribution density of eddy currents. They can be analyzed by the following formula: δ=1/πfμ0μrσ
Fatigue Design Philosophy of an Aero Engine Combustor Casing
Published in Sashi Kanta Panigrahi, Niranjan Sarangi, Aero Engine Combustor Casing, 2017
Sashi Kanta Panigrahi, Niranjan Sarangi
Eddy current testing uses the fact that, when an alternating current coil induces an electromagnetic field into a conductive test piece, a small current is created around the magnetic flux field, much like a magnetic field is generated around an electric current. Eddy currents can be produced in any electrically conducting material that is subjected to an alternating magnetic field (typically 10 Hz–10 MHz). The alternating magnetic field is normally generated by passing an alternating current through a coil. The coil can have many shapes and can comprise between 10 and 500 turns of wire. The magnitude of the eddy currents generated in the product is dependent on conductivity, permeability, and the setup geometry. Any change in the material or geometry can be detected by the excitation coil as a change in the coil impedance. The most simple coil comprises a ferrite rod with several turns of wire wound at one end; and is positioned close to the surface of the product to be tested. When a crack, for example, occurs in the surface of the test piece, the eddy currents must travel further around the crack and this is detected by a change in the impedance. The flow pattern of this secondary current, called an “eddy” current, will be affected when it encounters a discontinuity in the test piece, and the change in the eddy current density can be detected and used to characterize the discontinuity causing that change. A simplified schematic of eddy currents generated by an alternating current coil (“probe”) is shown in Figure 2.11. By varying the type of coil, this test method can be applied to flat surfaces or tubular products. This technique works best on smooth surfaces and has limited penetration, usually less than ¼ in.
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
Eddy current testing is a versatile technique for inspecting electrically conductive materials. The impedance of an inspection coil is affected by the presence of an adjacent test piece, in which alternating (eddy) currents have been induced by the coil. The net impedance is a function of the composition or geometry of the test piece. The popularity of eddy current testing is due to the convenient, rapid, and non-contact nature of the method. By varying the test frequency the method can be used for both surface and subsurface flaws. Limitations include the qualitative nature and the need for an electrically conductive test piece.
Fundamental study on smart eddy current testing for identification of crack orientation by controlling electromagnetic field using electrically anisotropic plate
Published in Advanced Composite Materials, 2023
Xiaojuan Xu, Wataru Matsunaga, Koichi Mizukami, Yoshihiro Mizutani, Akira Todoroki
As mentioned earlier, eddy current testing is an electromagnetic NDT&E technique based on inducing electrical currents in the conductive material. The secondary magnetic field generated by the induced eddy currents impedes and affects the propagation of the primary electromagnetic field penetrated into a test piece. In our previous work [28], it was found that the distribution of the eddy current density induced in the electrically anisotropic materials depends on their electrical anisotropy heavily, and thus, inserting an additional electrically anisotropic plate between an EC probe and a test piece is proposed in this work. The idea for controlling the electromagnetic field using the inserted anisotropic plate is that the response signal given by the EC probe can be affected by the anisotropic conductivity of the plate. In other words, the space magnetic field can be changed and regulated by rotating the plate (electrical conductivity of the inserted conductor), thus making the field directional.
Non-contact visualization of fiber waviness distribution in carbon fiber composites using eddy current testing
Published in Advanced Composite Materials, 2018
In the present study, we developed eddy current testing to overcome the difficulties described above. Eddy current testing is a non-contact, non-destructive testing method that induces eddy current in a tested conductive material, and then find defects by detecting changes in eddy current near the defective zone through measuring magnetic field. Because eddy current testing allows single-sided measurements, it can easily inspect large areas. Eddy current testing can be used to inspect CFRPs because carbon fiber is electrically conductive. Bardl et al. reported that the fiber orientation distribution of woven CFRP can be visualized by eddy current testing [7]. Because a woven CFRP has periodically aligned carbon fiber bundles, the signals from the eddy current sensor will also be spatially periodic. Thus, a two-dimensional Fourier transform of the periodic signals can give the in-plane fiber orientation. However, there are no reports of a non-contact eddy current technique that can visualize in-plane waviness distribution and measure the size of waviness in non-woven CFRP. In the present study, we visualize in-plane waviness by visualizing the path of the eddy current flowing along the carbon fiber. We propose a method to obtain the in-plane waviness distribution and a magnetic imaging method for non-contact measurement of waviness size. To validate these methods, we performed experiments and used the finite element method (FEM).
Influence of Core and Shield of Coil on Skin Depth in Eddy Current Testing
Published in Research in Nondestructive Evaluation, 2022
Maosen Chen, Yanfei Liao, Zhiwei Zeng, Junming Lin, Yonghong Dai
Eddy current testing (ECT) is widely used to detect surface and subsurface defects in conductive materials nondestructively. Due to the skin effect, which states that eddy current (EC) density decreases with increasing depth inside the conductor, deeply hidden defect is difficult to detect. The speed of EC attenuation in the depth direction is characterized by the skin depth, which is defined as the depth at which the EC density equals 1/e of the EC density at the surface of the conductor. When the excitation magnetic field is uniformly distributed, the skin depth in a linear, uniform, and isotropic good conductor with infinite thickness is given by