Investigation Of Digital Image Correlation Method In Damage And Fracture Experiment

Digital Image Correlation method (DIC), which is an optical measurementmechanics method, was originally developed from the1980’s of last century. It hasmany remarkable advantages such as non-contacted, full-field, low requirements onthe environment, simple optical setup, measurement field adjustable, and high degreeautomation etc. DIC method is one of the most active and perspective modern opticalmetrologies. The main content of this paper is to expand the scope of DIC method bysolving important problems appeared in the damage and fracture experiment. In orderto solve important problems appearing in the damage and fracture experiment, theextended DIC method is developed in this paper. The main achievements are asfollows:1. An effective method combining the deformation information and gray changeinformation, which is suitable for both brittle materials and plastic materials, ispresented to identify the material’s damage area. According to the experimentalresults, the method is suitable for identifying in terms of the damaged area of bothbrittle and plastic materials, especially the area with larger out-of-plane displacement.The experimental information of the whole entity deformation is also collected in thismethod, which can be used for real-time monitoring.2. An image stitching method is developed to measure percentage elongation ofbrittle material precisely. The relationship between the image before and afterdeformation is described by matrix, and the testing accuracy of rigid body translationand rotation is also investigated. Use method to measure What’s more, residual plasticdeformation of the local fracture area and the percentage elongation of standarddistance are measured. According to the comparison between the latter result withextensometer measurement result, the method is feasible with better applicability.3. Multiple fracture parameters are measured during three-point bending test.DIC method and gray correlation method is combined to identify crack, which canmake drawing the crack growth curve accurately. Crack opening displacement ismeasured to obtain the CTOD/CMOD-time curve, CTOD/CMOD-load curve. Sincethe stress intensity factors is based on the least-square fitting of local displacementfield, U-shaped area around crack tip is chosen as the fitting area. There is a good correlation between the theoretical results and the test results. Through the aboveparameters test, the DIC method can effective test a variety parameters in fractureexperiments.