Evaluation of the Residual Plastic Deformation in Low-Carbon Steel with the Oscillatory Rotating Eddy Current Method

Residual plastic deformation induced in low-carbon steels usually demonstrates anisotropy. Eddy current method is applicable for the residual plastic deformation evaluation. However, it is difficult to efficiently evaluate both the principal strain direction and magnitude of residual plastic deformation with the conventional eddy current method. To solve these limitations, a novel method of oscillatory rotating eddy current (OREC) was developed and successfully applied in characterizing the anisotropy of residual plastic deformation in low-carbon steels. The parameters of eddy current response obtained under different frequencies were extracted to characterize the plastic deformation and then the characterization performances of extracted parameters were compared. The compound voltage signal and real part of the impedance could better characterize the residual plastic deformation than the imaginary part of the impedance. It was found that the angle of the major axis of the selected 8-shaped patterns measured with OREC was a good indicator of the principal strain direction. As the residual plastic deformation was increased, the length of the major axis of the 8-shaped patterns monotonously increased despite its sensitivity to the plastic deformation was frequency-dependent.