Research On The Spatial Carrier Shearography Based On Michelson Interferometer

Digital Shearography is an optical technique for measurement of displacement derivatives, which is developed from Electronic Speckle Pattern Interferometry (ESPI). Shearography not only exhibits such characteristics as non-contacting, real-time, high-sensitivity and full-field of ESPI, but it also has special advantages like simple optical setups, lax vibration isolation, insensitivity to environmental disturbances, high sensitivity to the strain concentration. The advantages have rendered shearography as a practical measurement tool for nondestructive testing in industry.For the rapid detection of the dynamic deformation of an object surface, this thesis researches key technologies about spatial carrier shearography and established a shearographic system. The main works of this thesis are as follows:1. Comparison analysis between several common shear imaging devices is investigated in detail. And spatial carrier technology both at home and abroad is researched as well. Michelson interferometer is proposed to be as both shear device and carrier device based on the above research.2. A spatial carrier shearographic system based on Michelson interferometer is designed. The optical path structure and the optical parameters are designed and chose in detail. The three major innovation of this system are analyzed: first, Michelson interferometer is used to generate spatial frequency shift; second, slit diaphragm is used for the spatial frequency division processing; third,4f system is used to achieve wide angle of view.3. The relevant image processing technologies of Shearography are studied, which mainly includes phase extraction method, phase map filtering and unwrapping algorithms. Different phase-shifting techniques are studied and compared with each other, verifying that the Fourier transform method has a great advantage for dynamic measurement.4. Experimental studies are conducted and show that the designed spatial carrier shearographic system can be applied to dynamic deformation measurements as well as NDT of composites effectively.