Research on Hardness Detection Method of Polyvinyl Chloride Cable Sheath Material Based on Laser-Induced Breakdown Spectroscopy

Surface hardness is one of the most important parameters which describes the degree of aging in polyvinyl chloride (PVC) cables. In this work, the hardness of PVC sheathing material was studied using laser-induced breakdown spectroscopy (LIBS). At first, the experimental samples were subjected to different time of aging. Then, the trends of ionic and atomic spectral line intensities of Ca elements in the samples were analyzed with the variation of sample hardness. The relationship between the ratio of intensity in Ca II and Ca I spectral lines and the hardness of samples was analyzed. It was found that there was an obvious linear relationship between the ratio of the intensity at Ca II 422.0071 nm and Ca I 429.8988 nm spectral lines with the hardness of samples. A hardness estimation model was built using the linear relationship between them. The coefficient of determination (R2), root mean square error of calibration (RMSEC), root mean square error of prediction (RMSEP), mean absolute error (MAE), and absolute relative error (ARE) of the model were 0.94749, 1.89411 HD, 2.78581 HD, 2.41794 HD, and 0.05981, respectively. In addition, the relationship between the plasma excitation temperature (Te) and the hardness of samples was investigated. There was a linear relationship between plasma excitation temperature and sample hardness. And the relationship between the plasma excitation temperature and sample hardness was used to build a shore harness tester (HD) estimation model. The R2, RMSEC, RMSEP, MAE and ARE of the model were 0.94802, 2.05762 HD, 1.90007 HD, 1.56976 HD and 0.0348, respectively. By comparing the above two models, it was found that the model for estimating the hardness of the plasma excitation temperature was better performing than the ion-to-atomic line ratio model. It was more suitable for estimating the surface hardness of PVC cables.