The Research On The Fatigue Crack Propagation Behavior Based On The High-resolution CT Imaging

2A50 wrought aluminum alloy gets a large number of applications in the aerospace industry because of its good plasticity and high strength characteristics. The structures of the aircraft tend to produce fatigue cracks under the bending loads and will threaten the safety during the flight. Determining the crack information is the prerequisite for the crack propagation analysis, and the crack propagation has typical three-dimensional characteristics, while the conventional non-destructive testing methods can’t obtain three-dimensional information of cracks.Therefore, in this paper, 2A50 wrought aluminum material was selected as the object of the study, and the high-resolution CT imaging method was used to do the research on three-dimensional crack propagation behaviors and damage characterization under bending load. Obtaining the specimens with cracks of different stages of the crack propagation by three-point bending test of 2A50 material,analyzing the information of the surface crack propagation by scanning electron microscopy. Using the high-resolution micro-CT scanning and reconstruction of fatigue crack to obtain the CT evolution images of different stages of crack propagation. Doing image registration performed for different propagation stages of crack in the CT evolution images, giving comparative analysis for the two-dimensional CT crack images of different fatigue propagation stages based on the registration images. The crack feature was successfully extracted by using the method of regional extraction, by using the three- dimensional visualization method to obtain three-dimensional shape of the cracks. The contrast of the cracks were improved by proposing infiltrating gallium in cracks, so as to obtain the enhancement image of the cracks, by using the three- dimensional visualization method to obtain three-dimensional shape of the liquid gallium. The four stages of fatigue crack images were projected on a two-dimensional plane to obtaining the incremental plane of crack growth, doing research on the characteristic of crack propagation on tow-dimensional plane based on calculating the crack front length on the plane. Proposing an algorithm of extracting the curved surface of single pixel thickness crack propagation, which canbe used to extract the middle of the curved surface of the body of the cracks, The four stages of fatigue crack images were projected on the middle of curved surface to obtaining the incremental image of crack growth on the curved surface of single pixel thickness, analysis the length and rate of crack propagation based on the curved surface of single pixel thickness of crack propagation, and obtained that the surface roughness of the curved surface of single pixel thickness of crack propagation was2.2206 pixels by calculation, can be used to reflect the severity of crack propagation in the thickness direction. The calculation model of risk factors of the crack propagation was put forward to evaluate materials fatigue life, the current risk factor is 0.25 by calculation, the current crack propagation is at risk..The results show that high-resolution CT technique can be used to detect the fatigue crack in the material. The three-dimensional information of the crack based on three-dimensional visualization can be used to analysis the three-dimensional propagation behavior of crack.