The Experimental Research Of Digital Holographic Photo-elasticity Method To Test Residual Stress Non- Destructively

Modern photo-mechanics techniques is an experimental subject which is mainly formed by the cross and combination of optics and mechanics, it uses modern optical measurement techniques and digital image processing techniques to measure engineering mechanical parameters fully with non-contact and high precision. There is a disadvantage in the traditional holographic photo-elastic method, that is the arithmetic line stripes, and line stripes will appear at the same time, mutual modulation will cause the confusion and error in stripe analysis, and line stripes are too close, arithmetic line stripes are too sparse, it’s not easy to calculate. Recently, there are some methods to separate the two groups of stripes, such as double model method, optical rotation method, and reflective interference method. But double model method needs to make two models with different materials and same sizes, and carries on the experiment under the identical conditions, otherwise it will affect the experimental results. Optical rotation method needs to add optical rotator, the light path is more complex, adjustment is difficult, so the error is great. Reflective interference method needs to coat with reflector on the model surface, the light path is also more complex, and the arithmetic line stripes is easy to deform. In order to solve these problems, the digital holographic photo-elastic method by rotating reference light polarization direction to detect transparent residual stress nondestructive putted forward by Li Junchang and Xu Wei who through the application of traditional holographic photo-elastic method combined with modern digital image correlation technique. With the completion basically of the experiment, we get the holographic images, images of object light and images of reference light, through the digital image processing and the solution of nonlinear equations to get the residual stress values finally.In order to verify the feasibility of this method, the following research work have been done in this paper:1. This paper using the basic theory of the digital holographic photo-elastic method by rotating reference light polarization direction to detect transparent residual stress nondestructive, we shoot on our new purchased epoxy resin specimens to get light intensity information distribution images.2. We test the residual stress values on the same specimens by drilling method, due to the small hole impacts the residual stress on the other position of the same specimen, we tested three photo-elastic specimens, the first two specimens were drilled in the central location to test the residual stress in the center position, the third piece of specimen was drilled in the two diagonal position, so the experiment tested the residual stress values of four points.3. Through the digital image processing, we extracted the light intensity of the corresponding points in the drilling method and got four equations, we solved the four equations and got the residual stress values of the corresponding points. Then to compare with the residual stress values by drilling method, the results of the two methods are basically identical, proving the correctness of the digital holographic photo-elasticity method.