Self-calibration Digital Image Correlation Technique For Testing In Engineering Measurement

With the rapid development of economy,science and technology,the scale of construction is expanding every day.In order to meet the needs of large-scale structure and bridge measurement,the continuous innovation and development of civil engineering experiment technology is important.Strain gauge,displacement meter,dial indicator and other traditional measurement methods are limited by the measurement conditions.Only a single point of single-direction approximation deformation can be measured.Digital image correlation method as a full-field,non-contact optical measurement method,can reflect the overall deformation of the specimen.However,for the large-scale components in the project and bridge,the general three-dimensional digital image correlation technology is facing the calibration difficulties and low accuracy.Therefore,this paper aims at engineering application,and uses the three-dimensional digital image correlation system based on speckle self-calibration.The basic principle,hardware construction and measurement precision of the system are studied and analyzed,which can meet the experimental requirements of engineering survey.The self-calibration digital image correlation system is applied to engineering experiments such as deformation of wood structure and large tank drop.The measurement parameters include point tracking,three-dimensional displacement,full-field strain and so on.In order to realize the long distance measurement at the engineering site,an image acquisition system based on the self-calibration digital image correlation method is build.The equipment parameters and arrangement of the system are given in the paper.The basic technology of three-dimensional digital image correlation method and the core principle of self-calibration of the external parameters of self-calibration camera are described.The advantages of self-calibration method relative to calibration plate are compared.The measurement accuracy is divided into two parts:displacement and strain.Through the accuracy verification experiment,the measurement accuracy of the self-calibration digital image correlation method is studied.The accuracy of in-plane displacement by self-calibration method can reach 0.3%and the displacement accuracy of the surface can be up to 0.6%,which is consistent with the accuracy of ordinary 3D DIC system.For the strain precision experiment,when the same four-point bending beam is measured,the results show that the average relative error of the two systems is 4%and the absolute error is within 50??.It is relative to the strain gauge measurement error of about 6%and meet the requirements of engineering measurement.For the structure of the long-range deformation measurement needs,the self-calibration digital image correlation system is applied to the test of the wooden structure.The deformation of several reinforced structure of the tenon structure of the wooden structure is measured.The deformation field on the whole structure of the component is obtained,and the displacement of the loading point in the test process is matched with the data of the displacement meter.The bending moment curve is drawn to provide the experimental basis for the reinforcement of the wood structure.Self-calibration digital image correlation is an effective way to achieve large field measurement.It was used to monitor the free fall and collision ground process of ductile iron high integrity container.The displacement and strain of the container surface were obtained.The measured values of the points are compared with the results of dynamic strain gauge near the collision point.The mechanical properties of the container under the impact can be given.It provides a reliable way for engineering measurement.