Research On Displacement And Strain Measurement Of Rotating Object Based On Digital Image Correlation

Digital image correlation(DIC)is a non-contact optical measurement method.Because of its simple operation,full field measurement and high precision,it has been widely used in many fields and solved many practical engineering problems.However,with the development of science and technology,the requirement of measurement is higher and higher,and there are some problems to be solved.For example,for the deformation measurement of rotating objects,the traditional DIC method will appear a large error,which is difficult to meet the actual requirements.To solve this problem,this paper proposes an improved DIC algorithm,which solves the problem of decorrelation caused by rotation and improves the accuracy of full-field displacement and strain measurement of rotating objects.In order to solve the decorrelation problem of the traditional DIC method when measuring the deformation with large rotation,this paper improves the DIC method and applies the improved method to the measurement of rolling bearing.The proposed method is a DIC method based on the rotating subregion.Firstly,the rough rotation Angle of the deformed subregion relative to the reference subregion is obtained by using the feature point detection technique;Secondly,the deformed sub-region is rotated and matched with the reference sub-region by integer pixels;finally,the proposed NR iterative algorithm based on rotated sub-region is used for accurate sub-pixel matching.The simulation results show that the method can effectively measure the rotation deformation of any angle,and the average correlation coefficient is 0.99,which can achieve high-quality correlation matching.The method is used to measure the movement of the bearing,and the two-dimensional displacement of the bearing and the trajectories in two directions are obtained.The results show that the method is suitable for the measurement of bearing motion and has a great application prospect in the on-line deformation measurement of rotating objects.This paper improves the traditional pointwise least square DIC strain calculation method of local displacement field,introduces the rotation matrix and virtual displacement field before and after deformation,and proposes a high-precision strain calculation method suitable for rotation deformation measurement.This method can solve the error problem caused by rotation strain measurement,so as to achieve high-precision strain measurement at any angle.In the simulation experiment,the same strain under different rotation angles and different strains under the same rotation angle were measured respectively.Compared with the traditional DIC method,the RMSE average value of the two experimental strain measurements decreased from 0.00498 to 0.00011 and from 0.00703 to 0.00027 respectively.In the cupping experiment,compared with the traditional DIC method,the proposed method reduces the average RMSE of strain measurement from 0.0059 to 0.0016.The above two experimental results prove that the proposed DIC strain calculation method can reduce the error of strain measurement under rotation condition,so as to obtain high-precision strain.