Magnetic indicators for evaluating plastic strains in electrical steel: Toward non-destructive assessment of the magnetic losses

Electric steel is widely used for magnetic conversion of electrical energy such as in electric motors and power transformers. Electric steel sheets are cut using mechanical methods (such as punching) during manufacturing. These methods induce local plastic strains, which lead to overall degradation in magnetic performance. Plasticity and magnetic losses are physically related in electrical steel. It is impossible to measure the magnetic losses on the production line using standard methods. Non-destructive testing (NDT) based on magnetization mechanisms is a promising alternative, giving access to local plastic strains and indirectly to local magnetic losses. In this study, a setup was designed to stimulate the magnetization mechanisms separately while maintaining the same experimental conditions. The magnetization processes related to the domain wall kinetics were revealed to be more correlated to plastic strain. The magnetic incremental permeability hysteresis area and maximal value, and the coercivity associated with Barkhausen noise were found to be the best plastic strain indicators. Additional tests in an NDT context confirmed the correlations, the equal applicability of the proposed indicators, and their viability in predicting static hysteresis loss.

Automated summary

Electric steel is commonly used in electrical energy conversion applications and is subject to plastic strain during manufacturing processes, which can degrade its magnetic performance. This study proposes non-destructive testing based on magnetization mechanisms to measure local plastic strains and indirectly assess local magnetic losses. Experimental results show that magnetization processes related to domain wall kinetics are more correlated with plastic strain. The magnetic incremental permeability hysteresis area and maximal value, as well as the coercivity associated with Barkhausen noise, are identified as effective plastic strain indicators. Additional tests confirm the correlations and applicability of these indicators and their capability to predict static hysteresis loss.