Single Beam Shearography와 실험식을 이용한 결함의 크기 예측

Abstract

In 1970's, a stress intensity factor in fracture mechanics had led to the need for quantitative nondestructive evaluation(QNDE) of a defect by NDT, which means that it is quantitatively determined with the characteristic of a defect such as position, size, shape and kind. Based on this factor, the reliability and life of a structure can be evaluated. With the advancement of science and technology, the demand for greater product quality and reliability has created a need for a highly efficient nondestructive testing method. Previous methods have been developing new techniques from contact to non-contact, from point by point to whole field, and with real-time. Among previous methods, UT and RT are well designed and rapidly developed for the inspection of inside defects. Laser application techniques have been applied for displacement measurement technique based on interferometer, laser based ultrasonic testing, Holography, speckle correlation interferometry etc. Particularly, speckle correlation interferometry can get the surface displacement on large area with real time, high resolution and non-contact basis, which gives the advantages in vibration analysis, deformation analysis and non-destructive testing. With computer science and image processing technology, film-based speckle correlation interferometry evolves into ESPI and Shearography, which substitute the film-based by the digitalized with CCD camera, frame grabber etc. Its basic idea was developed almost at the same time by Macovski, Ramasey and Scheafer in U.S.A. and Buttersand Leendertz. Phase shifting method developed by K. Creath makes ESPI more useful, which can automatically extract a phase from interference pattern and demodulate the surface displacement of a target. But ESPI has a vulnerable point that is sensitive to environmental disturbance for application to industry. That is a rule of general application in this field. The other side, Shearography is used widely for non-destructive inspection because of less sensitivity to environmental disturbance and simple interferometer. This paper proposes the out-of-plane displacement extraction technique from results of Shearography by numerical processing and measurement results of ESPI and Shearoraphy are compared quantitatively.