Emissivity correction of eddy current pulsed thermography for rail inspection

摘要

Eddy current pulsed thermography (ECPT) is an emerging non-destructive testing and evaluation (NDT&E) technique for conductive material. However, surface emissivity variation of metallic object influences accurate temperature mapping in infrared thermography, which leads to false alarm of defect detection. This paper proposes a new emissivity correction method for ECPT based on spectral reflectance measurement in infrared and visible wavelengths. A graphical indicator was calculated based on normalized difference vegetation index (NDVI) algorithm and utilized for reducing the influence of emissivity variation. Experimental studies were conducted on steel plate and rail samples with different calibrated emissivity to verify its capability for artificial and natural rail cracks characterization. Results demonstrated this method can effectively improve defect detectability of ECPT for rail inspection.