Measurement Of Surface Field Deformation Of Cylinder Specimen Based On DIC Method

In recent years,digital image processing and analysis of the development of technology has made great strides,and has been widely used in many fields of national economy,such as machining parts size detection,in the process of material science and analysis of metallographic figure identification,robot visual perception,etc.Among them,the digital image correlation method is a new method of experimental mechanics,to analyze the whole displacement and strain,and become an important civil engineering test image measurement method.Geotechnical triaxial tester is a kind of device to simulate the seismic state in the laboratory.In the process of test,triaxial test samples are usually made into cylinders to study the relationship between stress and strain.For a long time,it has been a difficult problem for geotechnical testing to measure the deformation on the whole cylinder specimen surface,which is especially important for studying the strength and deformation characteristics of the specimen.In order to solve this problem,a digital image correlation method is used to measure the surface deformation of cylinder specimen.The research contents and results of this paper are as follows:First,details refer to the relevant research literature at home and abroad,this paper introduces the basic principle of 2D digital image correlation method,and describes the system based on binocular stereo vision imaging model of 3D digital image correlation method and the implementation process of measurement system.Secondly,by using 2-d digital image correlation method to measure the deformation of the rubber film on the outer surface of the sample,the full-field deformation of the triaxial test sample surface can be measured.Against the cylinder sample test in the process of local small in-plane distortion problems,combined with its imaging characteristics in monocular camera image measuring system,this paper puts forward a cylindrical reverse projection algorithm for cylinder sample images to correct image distortion,and use the 2 d DIC across the surface deformation field information.Experiments in the process of precision calibration in elastomer as test object,selecting the load displacement curve as reference,the actual measurement results and the load displacement data,verify the accuracy and reliability of the algorithm in this paper.Finally,based on binocular stereo vision technology,a 3d image acquisition scheme of cylinder specimen is proposed,and the off-plane displacement information of cylinder triaxial test specimen surface is obtained.The internal and external parameters of the camera were calculated by using Zhang Zhengyou calibration method.Using the internal and external parameters of the camera,the surface image of speckle sample was reconstructed in three dimensions to obtain the three-dimensional spatial coordinates of the sample surface.Finally,the 3d deformation measurement of digital image correlation method is realized by solving the full-field displacement.