Research And Application Of Digital Image Correlation Method Based On Finite Element Formulation

Digital image correlation (DIC) method is an optical measurement mechanicsmethod which was originally developed from the1980’s of last century. It has manyremarkable advantages: non-contacted, full-field, low requirements on theenvironment, simple optical setup, measurement field adjustable, high degreeautomation etc, and can realize multiscale mechanical behavior test in combinationwith microscope. It can be said that DIC method is the most active and mostperspective one of modern optical metrologies. The main content of this paper is toimprove the theory of DIC and expand the scope of it.Digital image correlation method based on finite element formulation putforward by this paper is that the subset adopts finite element displacement mode. Forcontinuous subset, it is studied detailedly that measurement precision of DIC whensubset displacement mode takes4,8,9,12,16nodes unit displacement moderespectively. In view of uniform tensile deformation field and the deformation fieldnear the crack tip, it is raised that the optimal option of subset displacement mode.Uniform tensile deformation field measurement should adopt4-node unitdisplacement mode. The measurement of the deformation field near the crack tipshould adopt9-node unit displacement mode. For discontinuous subset, it is proposedthat the optimal options of iteration region of subset. It avoids the misconvergencephenomenon which is caused with the error of sub-pixel interpolation.The feasibility of DIC based on finite element formulation measuring elasticconstants for aviation composite materials accurately is studied. By proposing rationalplan for average strain test (two-dot method based on the extended meter principle)according to ASTM, it makes the strain measurement precision reach50με, meet thetest requirement of aviation composite materials. The elastic constants for threedifferent composite materials are measured by DIC and strain gauge methodsimultaneously. The results of the two methods are consistent. It demonstrates thatDIC can measure the strain of aviation composite materials accurately.The stress intensity factors of the mixed-mode crack of superhard aviationaluminum alloy are measured by DIC based on finite element formulation. It is raisedthat the crack tip coordinates is fixed by trying related calculation of crack-tip element. When the stress intensity factors of the mixed-mode crack measurement are based onthe least-square fitting of local displacement field, it is put forward that the optimalregion of fitting data is annular region in order to improve the test precision. Finally,the test values are made a comparison with the data from handbook. They meet witheach other well. It proves that this method can measure the stress intensity factors ofthe mixed-mode crack accurately.