The Fracture Surface 3D Reconstruction And Damage Analysis Of Welded Joint

This paper took fatigue fracture surface and fatigue characteristics of welded joint as the research subjects.Firstly, the stereo pairs technology and computer image processing technique were applied to reconstruct fracture surface. The scanning electron microscope (SEM) images of fatigue crack of welded joints obtained with two projection angles were used in the reconstruction. Initial matching were performed to extract and match feature points based on Scale Invariant Feature Transform (SIFT) algorithm, and the matched results were used to calculate fundamental matrix of the image pairs. In order to obtain good consistency with real fractures, this paper adopted Medial Absolute Difference (MAD) per-pixel matching method without interpolation process, in which epipolar constraint, unique constraint and maximum disparity constraint were used to find correct and dense matching points. Based on the per-pixel matching results, height calculating and 3D surface replaying method were applied to reconstruct crack surface.Secondly, fatigue tests of TC11 welded joint were also carried out, the fractal dimensions were calculated based on the actual 3D dimensions of the facture surfaces of welded joints, the relationships between fractal dimensions and fatigue test results were also obtained. On the basis of the fractal damage theory, a unified equation for fractal damage evolution of welded joint under fatigue load was derived.Finally,the evolution of fatigue damage of TC11 welded joint was studied. Based on the fatigue fracture mechanism, the micro-analysis of fracture surfaces were done to study the detail characteristics of crack source region, crack growth region and instantaneous crack area, and then the cause and evolution process of fatigue of TC11 welded joint were discussed.