Research On Structural Response Measurement Base On DIC In Thermal Enviroment

The thermal deformation of the spacecraft structure under the solar radiation environment changes the mechanical properties of the structure and reduces the normal performance of the aircraft.In severe cases,it will affect the safety of the aircraft.Therefore,it is very important to conduct thermal tests on the key structures of the aircraft during the ground test Necessary.Digital Image Correlation(DIC)method is a high-precision optical measurement method for measuring the surface deformation of an object.Compared with the traditional single-point measurement method of strain gauges,DIC can achieve full-field deformation measurement of the object surface because the non-contact measurement characteristics enable DIC to achieve thermal deformation measurement of structures that cannot be achieved by ordinary measurement methods.The two-dimensional and three-dimensional measurement methods under normal temperature are studied in this paper.The monocular and binocular measurement systems are built,and the effectiveness of the test system is proved through experiments.Focusing on the two key issues of structural thermal response measurement,namely the effect of optical glass window and the problem of large size measurement,the error effect of optical glass window on DIC measurement is analyzed and a regularization correction method is introduced;in-plane for large size structure 2.The out-of-plane thermal response measurement proposes a twodimensional and three-dimensional image stitching method based on DIC feature recognition.Based on the self-built high-temperature optical measurement system,the thermal response measurement test of the actual structure was successfully carried out.The work of this article includes the following aspects:1)Based on the frequency domain whole pixel search and IC-GN sub-pixel positioning method,a two-dimensional DIC measurement program was written,and simulation and experiment verified that the noiseless DIC calculation accuracy is better than 0.01 pixel,and the actual in-plane strain measurement accuracy is better than 200 micro-strains,the calculation speed reaches 2500 pixel / min.Based on the principle of binocular vision,a three-dimensional DIC measurement program was written.The rigid body translation test proved that the measurement accuracy in three directions was better than 0.05 mm.2)In view of the influence of the optical glass window on the DIC measurement,the error caused by the surface pollution of the glass on the DIC measurement was first proposed,and the concept of the surface pollution area ratio was established using a random white noise model.Through theoretical derivation and numerical simulation,the errors caused by refractive index,thermal deformation of the profile and surface pollution are analyzed.The denoising effects of Tikhonov,Total variation,and sparse regularization methods are compared and analyzed.Based on the above research,the measurement test under thermal environment was carried out and the in-plane thermal deformation field of aluminum alloy specimens in the range of 20 ～ 511 ℃was successfully obtained,and the reliability of the measurement results was verified by the thermal expansion coefficient calculation.3)For the measurement of the in-plane thermal response of large-scale structures,a 2D image stitching method based on DIC feature recognition was carried out;for the measurement of the out-of-plane thermal response of structures,a 3D image stitching method under a noncommon calibration field of view was proposed.Different from the high requirements for the calibration of the field of view during the traditional camera array test,the dual camera measurement unit is used to perform three-dimensional reconstruction independently,based on the two-dimensional DIC,the high-precision positioning and matching of the speckles in the small overlapping area,and the conversion matrix after the three-dimensional reconstruction is realized Optimization calculation,and finally complete the splicing of three-dimensional space coordinates.The effectiveness of the two-dimensional and three-dimensional image stitching method was verified by the rigid body translation test under normal temperature.A quartz lamp heating module and a camera array acquisition system were designed.The in-plane thermal response measurement of the 400 mm × 300 mm solar wing model and the out-of-plane thermal response measurement of the 500 mm × 500 mm stainless steel plate were carried out,and the two/three-dimensional thermal deformation field.of the structure was successfully measured.