Investigation of the surface crack inspection technique using electronic laser speckle pattern interferometry

摘要

Inspection of aged power plants and chemical plants has recently become important. These plants have many inspection regions and are various shapes, making it necessary to develop a non-contact inspection technique that enables flexible access to the objective inspection point. The optical inspection technique has therefore been well investigated as a non-contact inspection method. The authors investigated a new inspection method to detect surface cracks using electronic laser speckle pattern interferometry (ESPI) allows to inspect wide region to be inspected all at once. An elastic wave is generated on the object to be inspected, and vibration of this wave around a surface crack due to reflection or diffraction is measured by ESPI. This non-contact inspection thus enables inspection of a wide area at once. In this study, verification of principle for surface crack detection is performed using a steel ball that hits the surface to generate elastic wave. Detectability of the surface crack is confirmed using an EDM notch (length [mm], depth [mm]) = (60,12) to (15,3) made on a carbon steel plate by electrical discharge machining. The crack length can also be measured within an error of 15 to 30 percent.