Research On Second Order Shape Function Of DIC Method For Structural Deformation Measurement

In this paper,a digital image correlation method is used to measure the deformation(displacement and strain)of the structure.Digital Image Correlation method(DIC),a new non-contact optical measurement method,is used to measure structural deformation.Compared with traditional measurement methods,it has many advantages such as full-field measurement,strong anti-interference ability and high precision.After more than 30 years of development,Digital Image Correlation method are gradually perfected in theoretical research,and their application prospect is broad.It is a hot topic that domestic and foreign scholars study deeply.In civil engineering,mechanical engineering,aerospace engineering and other fields,DIC technology has a wide range of applications.However,there are still some thorny problems for researchers to solve in digital image correlation methods.Therefore,by reading Chinese and foreign references,review the relevant applied research results at home and abroad,and combining with the specific practice of this research team,this paper discusses the basic theory of digital image correlation method in detail.In this paper,the research on DIC strain measurement method is carried out by means of "Study on DIC method of second order Form function for Measurement of Structural deformation".The main work is summarized as follows:First of all,it reviews the research and development of digital image related methods over the past 30 years,introduces the breakthrough theoretical achievements and progress in this field,and summarizes the significant test applications of DIC methods in practical projects at home and abroad.Then the configuration and basic requirements of digital image correlation measurement system are introduced.This paper focuses on the basic principle of digital image correlation method and displacement search algorithm,including displacement shape function,correlation function,integral pixel displacement search algorithm,sub-pixel displacement measurement algorithm.Secondly,a main strain calculation method of digital image correlation method is introduced,and the strain calculation method of displacement field is calculated by local least square method.Aiming at non-uniform deformation,the influence of three mainstream subpixel displacement measurement algorithms on displacement accuracy is studied through digital simulation of speckle pattern.The newton-Raphson method is improved based on the second-order form function,the relevant theoretical formulas are derived in detail,and the technique of simulating speckle pattern formation is introduced,which is suitable for considering the displacement mode of the second-order form function.In order to verify the applicability of the proposed deformation measurement algorithm based on the second-order form function,the influence of mapping parameters on the displacement field was firstly studied,then the complex non-uniform deformation was calculated by numerical simulation,and the calculated results were analyzed.Then,the displacement measurement and strain measurement in the second order form function mode are carried out by using numerical simulation method for different orders and different calculation Windows,and the calculation results of this method and the classical Newton-Raphson method are examined.Finally,the GUI graphic calculation software suitable for the method in this paper is compiled by Matlab.Moreover,a practical example of the proposed method is given.