Research On Upsampling And Determing Displacement Location Method Under Frequency Domain

Digital image correlation method has the characteristic of non-contact and full-field detection and it is widely used in in many subjects and fields.However,at present the research of digital image correlation method is mainly carried out in spatial domain and there is no breakthrough in frequency domain research.One of the main reasons is that no effective method for obtaining sub-pixel spectrum information has been found.In this paper,the frequency spectrum sampling technology is studied from the perspective of frequency domain and a full set of displacement location method is proposed.The main conclusions and achievements of this paper are as follows:The upsampling technology is studied based on the two forms of frequency domain method—single peak method and double peak method,making the expanded spectrum distinguished to the sub-pixel level of displacement,which lays the foundation for subsequent accurate displacement location.In order to overcome the problem of low computational efficiency caused by direct use of upsampling technology and the inadequacy of computer memory,a method of applying upsampling technology in the range of 3×3 centered on the initial peak of spectrum—peak location method is proposed.The peak location method rapidly performs displacement positioning from coarse to fine according to a multiple of 1/k.In order to eliminate the influence of noise on the spectrum value,the quadratic surface fitting of the final data is used to further improve the displacement positioning accuracy.Because the frequency domain method performs a Fourier transform for a finite size window image,there will be spectrum leakage in the frequency domain.In order to reduce the interference of spectrum leakage on the spectrum value,a suitable window function is applied to the transformed data before the Fourier transform in frequency domain.In this paper,the spectrum properties of four window functions are discussed.It is found through simulation experiments that the accuracy of displacement location has been greatly improved after windowing operation.Finally,for the displacement of more than one whole pixel,the method of window translation is used to solve the problem that the calculation error increases with the increase of the whole pixel part of the displacement.The validity and accuracy of the displacement location method discussed in this paper are verified by the rigid body translation experiment.In addition,the oscillation frequency of the object and the elastic modulus of the nickel film were measured through this method.The above experiments show that the frequency domain displacement location method proposed in this paper is accurate and effective,and has broad potential application prospects in engineering measurement.