As explained in Chapter 1, the application of nondestructive techniques for NDT is intended for the early detection and characterization of anomalies in the material being evaluated. Because these defects have a negative influence on the mechanical performance of the mechanical part, NDT is an essential tool for quality assurance when manufacturing the part and maintaining it after the start of its service life.
There are several nondestructive techniques based on various physical principles. Usually the iteration between anomalies present in the material under study and the detecting medium (e.g., sound waves, electromagnetic radiation, etc.) is used to compare nondestructively measured or derived physical parameters with quantitative information generated by an anomaly present in the material. One such technique, based on eddy-current phenomena, involves measuring the change of the material impedance, which is affected by anomalies such as changes in the microstructure or cracks.
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