Panoramic Digital Image Correlation Method And Its Application In Pipe Deformation Measurement

At present,the pipeline is widely used in power machinery.The damage and deformation during service can cause serious consequences.Therefore,it is necessary to conduct comprehensive deformation measurements on them.Among various deformation measurement methods,digital image correlation(DIC)is widely used in engineering measurement due to its advantages such as simple experimental equipment,less impact from environmental conditions,and no damage to the specimen during the measurement process.The traditional dual camera 3D digital image correlation system is difficult to directly apply to the deformation measurement of pipelines due to its inherent shortcomings,such as the inability of two cameras to simultaneously capture a 360 degree full circumference image of the inner wall of the pipeline,and the inability to capture the same position of the inner wall of the pipeline when shooting at a certain angle.In order to solve the above problems,this paper combines panoramic imaging with unfolding technology and digital image correlation methods,and proposes a panoramic measurement technology for pipeline interior based on digital image correlation methods.The main research and work contents of this article are as follows:1.A three-dimensional panoramic digital image correlation system of flat mirror is developed,which uses prismatic mirror to measure the full 360 degree internal surface deformation.The system reflects the image information of the inner wall of the pipeline through the four faces of the right prism to realize panoramic observation,and converts the reflected image information of the four faces of the prism into the real digital image information of the inner wall of the pipeline through mirror coordinates.The three-dimensional displacement and strain distributions are reconstructed.The efficiency and accuracy of 3D shape and displacement measurement were evaluated by shape recovery and rigid body displacement experiments.The experimental results are in good agreement with the actual values and data obtained by many measurements using the traditional 3D digital image correlation method.In addition,the method has been successfully applied to the internal deformation distribution of pipeline under compression load,and the applicability of the method is further verified by the analysis of the experimental results.2.A curved mirror panoramic 3D digital image correlation system is proposed,which is composed of the principle of coaxial double camera,the principle of curved mirror panoramic reflection and expansion,the correlation method of double 3D digital image and pole coordinate transformation.Firstly,the optical path model of the coaxial system is established,and the measurement process is introduced.Finally,the accuracy of the coaxial principle is proved to meet the experimental requirements through verification experiments.The virtual image of the inner wall of the pipeline is reflected by a curved mirror and the panoramic image is developed into a plane rectangular image by using the principle of concentric ring approximate expansion.The three-dimensional digital image correlation method is used to match the expanded planar rectangular image and obtain the deformation distribution of the pipeline under the expanded state.Finally,coordinate transformation of plane coordinate points was carried out to obtain the morphology and deformation information of pipeline in real size.3.The curved mirror panoramic digital image correlation system was used to measure the size and displacement of the pipeline.In the topography reconstruction experiment,the error between the size of the pipeline measured by the system and the actual size of the pipeline was no more than 0.05 mm,and the maximum relative error in the overall displacement measurement of the pipeline was less than 2%.The subsequent load is applied to the pipeline,and the variation law of three kinds of displacements(lateral displacement,longitudinal displacement and out-of-plane displacement)under different loads is measured.Then the strain distribution of the pipeline under different loads is calculated through the displacement.Finally,the deformation information of the pipeline under different loads is analyzed to obtain the mechanical properties of the pipeline under compression.