The Growth Mechanism Study And Three-Dimensional Reconstruction Of 2A12 Aluminum Alloy Fatigue Crack Under Complex Stress State

With the improvement of industry and the following increasing demands for kinds of materials, make the study of materials’fatigue mechanism to be more and more urgent. Since the fatigue problem has been studied for more than 100 years, a lot of remarkable achievements have gained through the huge efforts by researchers and engineers, and investigations of the fatigue crack are no longer confined to the surface and two dimensional level, besides the rapidly improving technology of CT(Computed Tomography) scanning recent years provides a new way to study fatigue cracks. This article is a combination of 2A12 aluminum alloy fatigue test and surface crack growth behavior track observation, industrial computed tomography scanning, image denoising processing technology and 3d reconstruction technology, comprehensively researched the three-dimensional growth feature of 2A12 aluminum alloy.The low cycle fatigue tests of 2A12 aluminum alloy bars with annular notch under complex stress state were firstly conducted, include the fatigue life study of different nominal strain amplitudes (0.30%,0.40,%0.50,0.60%) with the same specimen size (R4), and the life, crack initiation mechanism, and growth feature contrast research for specimens with R3, R4, R5 notches under the same strain amplitude (0.56%). Results of tests showed that the crack initiation life and whole fatigue life were about dozens of thousand cycles which is convenient to observe the crack growth behavior. The crack initiation most caused by the black impurity undissolved phase debonding from the basal body or self-fracture and then growth integranular. And after the one or several cracks initiated and propagating will accompany with new crack initiation which maintained independent growth until the distance between cracks became close sufficient. In addition, some cracks’propagation morphology presented as a zigzag path in crystallography crack with the influence of local microstructure like slip band, and had a slight protuberance shape and tree-branch-like damage morphology under the CCD camera.Computed Tomography scanning technology and image processing like contrast enhancement, binaryzation, and outliers remove have utilized to obtain the precise crack morphology and size. As the view of treatment effect, binaryzation is a potent way to separate the crack and alloy material information in tomography slices which in favor of following observation and process, and outliers remove is appropriate to deal with sections for specimens have simple structure and relatively continuous crack distribution, additionally more clear crack images are possible by adjusting the radius of denoising. Final three dimensional reconstruction used matlab software and gained the 3D visualization of crack which agree well with the actual specimen.