The theoretical base of the low frequency impedance method and possibilities of its use in the diagnostics of paramagnetic and ferromagnetic alloys (including welds) used in transport and power engineering has been explained in the article. The main attention has been paid to the measurement of stresses in the material using low-cost measurement path, e.g. handheld automated LCR meter. During laboratory tests with five signal frequencies designated relationships describing the impact of stress on the parameters of impedance. Example results are illustrated. For quantitative analysis of observed changes in impedance used precise mathematical formulas that describe the measured resistance and inductance core with its geometry and identifiable material parameters (permeability, conductivity and permittivity). Based on the obtained results it demonstrated the possibility of using low-frequency impedance spectroscopy (multi-frequency eddy currents) and low-cost measuring equipment to monitor the level of stresses. The method can be used in NDE and SHM applications.
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