Research On Strain Measurement Based On DIC Technology

As a modern non-contact measurement method,digital image correlation(DIC)method has the advantages of simple operation,high measurement precision and full-field measurement compared with the traditional measurement method.DIC technology has been studied and developed for more than 30 years.With the efforts of many scholars,it now has a relatively complete theoretical system which is often applied to the deformation measurement of practical engineering.However,the DIC method has much room to improve the accuracy of strain calculation.Therefore,based on a large amount of literature,this paper conducted further research on the strain calculation in the DIC method.The specific contents are as follows:Firstly,the basic theory of DIC method is presented in detail,and the research progress in this field at home and abroad was summarized,as well as the application status in engineering.A complete DIC measurement system was introduced,and the characteristics of several different correlation functions were compared.In the relevant search methods,this paper introduced 3 main methods,stepwise searching method,coarse-fine searching method,cross searching method,three step searching method,and the gradient method,Newton-Raphson method,surface fitting method in subpixel searching method.Secondly,several common methods of displacement measurement and strain calculation were summarized,and 2 new methods were proposed based on these methods,improved local variance method based on S-G filtering,improved weight NLM method based on S-G filtering.The specific idea of the two calculation methods was to smooth the original displacement field data and then the strain was calculated by the local least square method,so as to improve the accuracy of the calculation results.In order to verify the applicability of the two new methods,4 deformation conditions,namely large uniform strain deformation,small uniform strain deformation,uniform strain deformation with noise added and non-uniform strain deformation,were generated through using the simulated speckle pattern respectively.Two new methods were put in to verify the feasibility of the method,and the calculated results were analyzed and compared.Finally,the DIC method was introduced into the GUI interface in Matlab for the compilation and design,and the unidirectional stretching experiment with elliptical orifice is designed to verify the two new methods proposed in this paper,The results show that the new method can improve the accuracy of strain calculation.