Research On Dynamic Defect Detection In Shear Speckle Interferometry Based On Polarization Phase Shift

Laser shearing speckle interferometry is an optical measurement technique that can measure the surface displacement derivative of an object.In addition to inheriting the fullfield,non-contact,high precision,and high sensitivity characteristics of digital speckle interferometry,it also has the advantages of insensitivity to rigid displacement and strong environmental adaptability,and is widely used in non-destructive testing of composite materials.In this paper,aiming at the practical engineering application requirements for defect detection rate and deformation measurement of composite materials,a shearing speckle interferometry optical measurement method based on polarization phase-shifting is proposed.A shearographic interferometry measurement system with a simple and compact structure and strong anti-interference ability is designed to achieve real-time and fast dynamic measurement of defects.The main research contents of the paper are as follows:1.In the thesis,by studying the basic principles of laser shearing speckle interferometry measurement and comparing and analyzing several typical shear paths and phase-shifting techniques,a digital shearing speckle interferometry system based on a combination of a Wollaston prism and a micro-polarizer array is proposed for dynamic measurement requirements in composite material testing.Relevant digital models are established.The system adopts a micro-polarizer array phase-shifting method,which can instantly collect four shear speckle interferograms with phase shifting quantities that differ by n/ 2,achieving dynamic real-time measurement of defects.2.A window-adaptive sine-cosine filtering algorithm is proposed for high-frequency noise in speckle interferometry wrapped phase maps.The wrapped phase maps are denoised and filtered.Combined with the least-squares unwrapping algorithm based on fast Fourier transform,the phase solving speed and accuracy of the shearing speckle interferometry phase maps are effectively improved.At the same time,a large field of view and high uniformity laser illumination beam expander device is designed.The mechanical structure of the shearing speckle interferometry system is designed and assembled to meet practical requirements.3.For defects in different types of composite materials,the self-designed shearing speckle interferometry is used for full-field real-time and dynamic non-destructive testing verification.In the experiment,vacuum loading and thermal loading were used to cause deformation at the defects of the composite material test pieces.The results showed that the system designed in this paper not only has a high detection rate for defects of different sizes and positions in the composite material test pieces,with a maximum detection rate of 93%,and the smallest detected defect size is 2mm,but also can observe the dynamic deformation characteristics of composite material defects in real-time and accurately measure the displacement value of the defects off the surface at the micron level.