Remote inspection of surface cracks in metallic structures with fiber-guided laser array spots thermography

In this work, a fiber-guided laser array spots thermography (LAST) system with good flexibility is proposed for the inspection of surface cracks in metallic structural objects with difficult access. To generate an array of laser spots on the target surface, an optical head with fiber delivery is designed and fabricated at first, which has good adaptability and robustness. Second, a numerical simulation model is developed to optimize the spatial distribution of the laser spots. In addition, an improved image processing method with use of multiple background free images is developed to enhance the crack detectability from the LAST images. Finally, cracks of different types in stainless steel specimens are successfully detected from the thermal images obtained using the fiber-guided LAST system.