Infrared Lock-in Thermography Crack Localization on Metallic Surfaces for Industrial Diagnosis

Optical lock-in thermography with a modulated laser excitation is used for the qualitative assessment of surface cracks in metallic samples. In order to identify and localize an open defect, a novel dedicated image processing of the recorded IR amplitude sequence is proposed. The obtained results demonstrate the potentiality of active lock-in thermography as a contactless measurement tool for the localization of breaking cracks located into specific regions difficult to reach by other conventional non-destructive testing (NDT) techniques such as eddy currents or ultrasound techniques. Crack localization without a prior preparation of the inspected surface can be a possible alternative to penetrant inspection in industrial processes. Various applications illustrating the proposed procedure are presented.