Evaluation for Crack Defects of Self-Lubricating Sliding Bearings Coating Based on Terahertz Non-Destructive Testing

In this study, a non-destructive testing method for crack defects of self-lubricating sliding bearing coating based on terahertz time-domain spectroscopy was proposed. The self-lubricating coating materials were revealed to have good penetration and characteristic response in the terahertz band through experiments. To solve the problem of difficulty in signal feature extraction caused by overlap, the broad learning system was used to classify and predict time-domain signals of crack defects. The identification accuracy for crack defects is 96.08%, and the mean relative errors of prediction for interface and internal cracks (5 to 95 mu m in size) are 4.16% and 3.40%, respectively. The method proved the applicability for qualitative and quantitative evaluation in crack defects, which is considered a new idea for the non-destructive testing of self-lubricating coating.