Investigation of Skewness Feature for Evaluation of Defects Using Eddy Current Pulsed Thermography

The quantitative non-destructive evaluation (QNDE) of complex defects remains as challenges. The transient thermal responses of 3D eddy current pulsed thermography (ECPT) contains rich information for the defect characteristics. In this paper, a modified skewness feature extracted from the transient thermal responses is proposed for the QNDE in 3D ECPT. Different stages of the transient responses and their skewness features are experimentally investigated for angular cracks. The skewness feature is mapped to 3D point cloud captured by a 3D ranger in order to show the 3D skewness feature distribution. The heating stage is modified and inverted before the calculation of the entire transient thermal response due to different behaviors of skewness features at different transient stages. Results show that the modified skewness removed the counteracting effect of the temperature distribution in the heating stage and cooling stage, which make the modified skewness feature has higher sensitivity and linearity for the evaluation of defect depths.