Three-Dimension Strain Measurement Method Based On 3D-DIC

In the field of offshore oil and gas engineering,large structures such as offshore platform derricks and subsea pipelines are susceptible to fatigue breakdown due to wind,waves and corrosion.Marine accidents can cause significant economic loss and environmental pollution.One of the essential means to analyze the stability of structures is to accurately measure the displacement and strain on the surface of objects.Conventional contact measurement is complicated and can only apply to points.ThreeDimenson Digital Image Correlation(3D-DIC)is a multiscale,full-field,non-contact optical technique to measure deformation of structures.We utilize 3D-DIC and binocular stereo vision for 3D reconstruction of the object surface to achieve 3D coordinate,displacement and strain measurements.The main work is as follows:First,we propose a stereo measurement method based on 3D-DIC and study the principle of binocular stereo vision 3D reconstruction.We also build the experimental installation and analyze the applications of binocular convergent and binocular parallel reconstruction in detail.Finally,the optimal settings and experimental operation scheme in the process of camera calibration and image collection are summarized.Second,we test two key steps in the new approach.For camera calibration,we analyze the factors affecting camera calibration accuracy,including size,flatness,position and corner point accuracy of calibration plate.We provide a method to improve the camera calibration accuracy,and the reprojection error is reduced from 1.09 pixels to 0.40 pixels.Natural surface and speckle surface are selected for stereo matching test.The matching algorithm of this thesis is compared with Ncorr,and the mean error of two methods is 0.075 pixel.Finally,The core codes of reconstruction and displacement are written.Meanwhile,we also design the interface of software and package it.Rigid displacement of the cylinder is analyzed by 3D-DIC software.The results show that 3D coordinates and displacements are consistent with the truth.The software has a good feasibility in 3D measurement.