Shearography is a very effective non-destructive testing method for detecting the internal defects of composite materials. How to improve the detection efficiency of this technique to help achieve the rapid and automatic recognition of multiple defects has always been a hot research topic for researchers. Based on the results of the shearography, we propose a method to identify multiple defects in the phase map using the spatial characteristics of Freeman chain code. First of all, we use Canny operator to binarize the phase map, then refine the fringe by morphological means, and finally identify the defects by the spatial characteristics chain code. In addition, Otsu is used to assist in judging the fracture or incomplete defects. For the fringes under vacuum loading or thermal loading, this method can detect the defects quickly and successfully. The theoretical description is given and the effectiveness and practicability of the method are verified by experiments.
Digital speckle pattern interferometry (DSPI) is a high-precision measurement method for measuring the surface deformation of an object. Compared with other measurement techniques, it has the advantages of full-field measurement, real-time, non-contact, high precision and high sensitivity, which has made the technology widely concerned by the measurement community since its birth. However, the application calculation of most of the existing digital speckle interference is based on the paraxial and approximate vertical calculations, ignoring the large fluctuation range of the angle between the laser illumination direction and the CCD observation direction. It makes the measurement error of large field of view larger when the size of the object is large . Therefore, when measuring a large field of view, it is necessary to correct the existing measurement formula. This paper proposes a new method for applying digital speckle interference to large field of view measurement. Based on the basic principle of digital speckle interferometry, the corresponding compensation coefficient is obtained through mathematical relationship to compensate the measurement result of large field of view.
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