Thermal nondestructive testing using active line-scanning infrared radiometry

A modular, versatile system for thermal nondestructive testing using active line-scanning infrared radiometry was designed, assembled, tested, and applied in practice. The concept is based on the localized line-heating of the sample under inspection. Possible defects affect the heat flow in the sample, and thus also its surface temperature distribution. By translating the sample perpendicular to the heating line and simultaneously monitoring its thermal response with an infrared line-scanner, it is possible to record thermal images which reveal sub-surface irregularities in the sample. Theoretical analysis with finite difference simulations facilitates optimizing the system setup and the measurement parameters. The feasibility of the system and specific advantages of the method are demonstrated with both experimental and actual nondestructive testing of traditionally impossible or difficult samples, including carbon fiber reinforced aerospace composites and plasma-spray coated critical nuclear power plant components. The system has proven to be ready for use as an efficient tool for near-surface (max. few millimeters) defect detection and mapping in intermediate-sized samples with planar or one-dimensionally curved geometries. In this application range, the system may often turn out to be the most attractive inspection device.