Magnetic Barkhausen Noise Testing: Steel Grades and Stress Response
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Magnetic Barkhausen Noise emissions are discontinuous magnetization changes within ferromagnetic materials that have been subjected to changing applied magnetic fields. These emissions are sensitive to microstrutural variations and stress states of the material, which can adversely affect magnetic properties or structural integrity of engineering components. Therefore, magnetic Barkhausen noise has potential as a non-destructive testing technique for indirect materials evaluation. However, simultaneous dependence of Barkhausen noise emissions on metallurgical variables, physical features and stress state of the material complicates its data interpretation. The purpose of the present thesis was, therefore, to address these complexities by comparing Barkhausen noise signal characteristics from different ferromagnetic steel grades, all using the same measuring system under reproducible flux-controlled magnetization conditions. This is in contrast to the majority of literature Barkhausen noise investigations, which have focused on case studies using different probes and systems under unknown conditions of flux, which therefore limits their comparability. Various steel grades were tested, including transformer and electric motor laminates, submarine hull steel, deep-drawing steel and low to high plain carbon steels. Barkhausen noise signal parameters were correlated with core loss, grain size, crystallographic texture, hysteresis characteristics and the amount of carbon content. The significant contribution of this thesis was to examine the influence of steel grade on tensile stress-response of Barkhausen noise. The experimental results were explained in terms of domain wall dynamics and a basic theory was developed as a starting point to model the behavior mechanism of Barkhausen noise under tensile stress. This work contributes to the further development and calibration of Barkhausen noise technology for magnetic non-destructive assessment of ferromagnetic steel components.