Modal Parameter Identification Based On Digital Image Correlation Method In High Temperature Environment

The surface of hypersonic vehicle will become thousands of degrees due to aerodynamic heating in service environments,which can cause changes in the physical properties of materials.At the same time,the uneven temperature of each part of the structure will generate thermal stress,which will change the mechanical properties of the structure.Therefore,studying the influence of high temperature environment on structural vibration characteristics is significant.An improved algorithm is proposed to calculate the gray gradient of the image by the Tikhonov regularization method and the sub-pixel displacement of the image by the IC-GN method,which enhances the noise robustness of the algorithm in actual measurement.The dynamic response of the structure under normal temperature environment is obtained based on the non-contact optical measurement method.The modal parameters of the structure are calculated by the digital image correlation method,and the calculation results are compared with the traditional measurement results of hammer based on the acceleration sensor,which verifies the feasibility of applying the digital image correlation method to the measurement of structural modal parameters.A high temperature non-contact optical measurement system is built,and the modal parameters of the structure in high temperature environment are obtained.The detailed contents of the study are listed as follows:(1)An improved algorithm is proposed to calculate the gray gradient of the image by the Tikhonov regularization method and the sub-pixel displacement of the image by the IC-GN method.The anti-noise ability of the improved digital image correlation method is verified based on numerical simulation and experiment.(2)The normal temperature modal measurement experiment based on digital image correlation method is carried out,and the calculation results are compared with the traditional measurement results of hammer based on the acceleration sensor,which verifies the feasibility and effectiveness of applying digital image correlation method to modal measurement under normal temperature environment.(3)The digital image correlation method is further applied to high temperature modal measurement,and a high temperature non-contact measurement system is built.The use of band pass filters and blue illumination reduces the effect of high temperature intense light radiation on the measured data.The self-made high temperature speckle overcomes the shortcomings of the traditional speckle which is not resistant to high temperature.Finally,the modal parameters of the structure under high temperature environment are calculated by the digital image correlation method.