Research On Nondestructive Testing Technology Of Digital Speckle Shearing Interferometry

The key to digital shearing speckle interferometry(DSSPI)lies in the introduction of phase shift technology,which can directly detect the deformation or displacement derivative in the shear direction,and it is widely used in non-destructive testing of component materials-composite materials in aerospace,automobile industry,machinery manufacturing and other industries,but there may be various types of defects inside the composite material,which will seriously affect the service life of the product,and even cause loss of personnel and property.Although at present there are many ways to detect defects in composite materials,there are still many deficiencies in the simultaneous detection of different types of defects or the detection of some special materials(mirror or smooth surface objects).To solve these special problems,this paper proposes an optical non-contact nondestructive testing method of full-field speckle shear interference with high precision and high sensitivity,and establishes a coaxial cage measuring system with good stability to achieve real-time and dynamic measurement of defects.The research work of this paper mainly includes the following points:1.The principle of shear speckle interferometry,the basic principles of time phase shift interferometry and spatial phase shift interferometry are expounded,and the influence of various parameters in spatial phase shift interferometry on the test is explored,and proposed.corresponding improvements.2.Aiming at the possibility of missing detection of defects in a specific direction in the single carrier frequency method,the principle of shear speckle interference in two directions and two carrier frequencies is described in detail.The independent optical components are built into a coaxial cage structure system,and two-way verification experiments are carried out on the tested object.A set of 4f-based single-shear test system is also built,which can simultaneously obtain high quality images of temporal phase-shift interferometry and real-time dynamic measurement of space carrier interferometry.3.Aiming at the existence of interference noise in fringe image,and there will be large errors in the results of later phase unpacking and image inversion,etc.The filtering algorithms such as sines and cosines filter,fast non-local mean filter based on wavelet packet transformpath algorithm,and then unpack and verify the algorithm.4.In view of the fact that the system cannot directly measure the measured objects on mirror or smooth surface,the method of secondary scattering imaging is adopted,and the dual-direction dual-carrier system is used to measure the object with a mirror surface or smooth surface by thermal loading.Inspection,you can get a more obvious defect fringe pattern.The defects of composite materials can be measured by thermal loading or vacuum loading.At the same time,after thermal loading of a certain composite material,the shear directions are respectively detected,and the dynamics of the defects in the two shear directions can be clearly observed.The dynamic changes of defects can be observed more clearly after color processing of the filtered interference fringe pattern.The measuring sensitivity can reach 30 nm,the minimum detectable defect size is 5mm,and the measuring field of view can reach 1000mm×1000mm.