基于高分辨率CT成像的疲劳裂纹扩展行为研究

发布时间：2018-05-08 01:13

本文选题：高分辨率CT + 图像配准　；参考：《南昌航空大学》2015年硕士论文

【摘要】：2A50铝合金由于其塑性好、强度高,因此在航空工业中得到了大量的应用。飞机结构在飞行过程中受弯曲载荷作用易产生疲劳裂纹,对飞机安全飞行带来严重威胁。裂纹信息的确定是裂纹扩展分析的前提,而裂纹扩展具有典型的三维特征,常规无损检测方法无法获取裂纹的三维信息。因此,本文以2A50锻铝材料作为研究对象,提出采用高分辨率CT研究弯曲载荷作用下材料三维裂纹扩展行为和损伤表征。通过2A50锻铝三点弯曲试验得到不同裂纹扩展阶段的疲劳试样,通过扫描电镜分析表面裂纹扩展信息。利用高分辨率显微CT对疲劳试样进行扫描与重建获取不同阶段的裂纹扩展CT演化图像。对不同扩展阶段裂纹CT演化图像进行了图像配准,根据配准图像对不同疲劳扩展阶段二维CT裂纹图像进行了对比分析。利用区域提取法成功提取裂纹特征,并通过三维可视化方法获得裂纹三维形态。利用液态镓渗入到裂纹体内,提高了裂纹图像对比度,得到了增强显示的裂纹CT图像,通过三维可视化获得了液态镓的三维分布。将4个疲劳阶段裂纹图像投影在二维平面上,通过计算平面上裂纹前沿裂纹长度研究二维平面上裂纹扩展特性。提出了一种单像素厚度的裂纹扩展曲面提取算法,可用于提取裂纹体的中曲面,将4个疲劳阶段裂纹投影到该中曲面上获得了单像素厚度裂纹扩展曲面增量图形,根据单像素厚度裂纹扩展曲面分析了裂纹扩展长度和裂纹扩展速率,并计算得到单像素厚度裂纹扩展曲面的表面粗糙度为2.2206个像素点,可用于反映裂纹在厚度方向上扩展的剧烈程度。提出了裂纹扩展危度因子计算模型,计算得到当前危险度因子为0.25,当前裂纹扩展处于危险阶段。结果表明,高分辨率CT技术可用于检测材料中存在的疲劳裂纹,三维可视化得到的裂纹三维信息可用于分析裂纹的三维扩展行为。
[Abstract]:2A50 aluminum alloy has been widely used in aviation industry because of its good plasticity and high strength. The fatigue crack of aircraft structure is easy to be caused by bending load during flight, which is a serious threat to the flight safety of aircraft. The determination of crack information is the premise of crack growth analysis, and crack propagation has typical three-dimensional characteristics. Conventional nondestructive testing methods can not obtain three-dimensional crack information. Therefore, in this paper, high-resolution CT is used to study the three-dimensional crack propagation behavior and damage characterization of 2A50 wrought aluminum material under bending load. The fatigue specimens of different crack growth stages were obtained by three-point bending test of 2A50 wrought aluminum. The surface crack propagation information was analyzed by scanning electron microscope (SEM). Fatigue specimens were scanned and reconstructed with high resolution microCT to obtain the evolution images of crack propagation CT at different stages. In this paper, the CT evolution images of cracks in different growth stages are registered, and the 2D CT crack images of different fatigue growth stages are compared and analyzed according to the registration images. The crack feature is extracted successfully by region extraction method, and the 3D shape of crack is obtained by 3D visualization method. Using liquid gallium to infiltrate into the crack body, the contrast of the crack image is improved, the enhanced CT image of the crack is obtained, and the three-dimensional distribution of liquid gallium is obtained by 3D visualization. Four fatigue phase crack images were projected on a two-dimensional plane, and the crack propagation characteristics on the two-dimensional plane were studied by calculating the crack front length of the crack front in the plane. A single pixel thickness crack propagation surface extraction algorithm is proposed, which can be used to extract the middle surface of the cracked body. Four fatigue stage cracks are projected onto the middle surface to obtain the incremental figure of the crack propagation surface with single pixel thickness. According to the single pixel thickness crack propagation surface, the crack growth length and crack growth rate are analyzed, and the surface roughness of the single pixel thickness crack propagation surface is calculated to be 2.2206 pixels. It can be used to reflect the intensity of crack propagation in the thickness direction. A model for calculating the risk factor of crack growth is proposed. The current risk factor is 0.25, and the current crack growth is at a dangerous stage. The results show that the high resolution CT technique can be used to detect the fatigue crack in the material, and the 3D visualization of the crack can be used to analyze the three-dimensional propagation behavior of the crack.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.21;TP391.41

【参考文献】