Measurement System Based On Digital Image Correlation For Large Size Components And Experimental Research

In order to monitor the protection condition of the shipwreck of Song Dynasty in Quanzhou Bay,a method called digital image correlation,which is recognized by the industry,was introduced to measure the surface deformation of the shipwreck of Song Dynasty.Because there are more large size components in the shipwreck of Song Dynasty,and the environmental illumination for protecting shipwreck is low and varying,the application of digital image correlation method meet a challenge.As a monitoring system for comprehensive analysis of the deformation conditions of shipwreck,it should by ensured that the accuracy of calculation is consistent.There is a speckle image with high contrast on the surface of the object during using digital image correlation method.Because the environment illumination for protecting shipwreck is Iow and varying,and the natural textures on the surface of the shipwreck are different,the contrast of the speckle image on the surface will change due to the change of time and position,and it's impossible to ensure that the calculation accuracy of the digital image correlation method is consistent at all times.By deriving the error formula of digital image correlation method based on zero-mean normalized sum of squared difference,a method to control the error by adjusting the exposure time is proposed.Industrial cameras commonly used in digital image correlation field have a smaller field of view than large size components of the shipwreck that are several meters long.Therefore,it is not possible to monitor the large size components of the shipwreck simultaneously using a single camera.Considering that the surface deformation of the shipwreck is quasi-static deformation,the camera is attached to the single-axis slide.The camera is moved by the slide table,and the images collected at different positions are stitched together to generate a panoramic image.Through the secondary development of the sliding table and camera control program,the open source soffware of digital image correlation is modified to realize the automatic process of image acquisition,image stitching and strain solution.