基于CT扫描的2A12铝合金疲劳裂纹三维重建方法研究

Three-dimensional Reconstruction Method Study of 2A12 Aluminum Alloy Fatigue Crack Based on Computed Tomography

对中心处含圆形缺口的2A12铝合金圆柱形试样进行复杂应力状态下的低周疲劳试验,总结出材料裂纹萌生及扩展机制。试验结果表明,复杂应力条件下2A12铝合金材料只有在疲劳循环较大时,由于第二相粒子与基体脱粘形成疲劳短裂纹。裂纹扩展过程中,沿着晶粒某一滑移系统滑动并且形成锯齿形状的晶体学裂纹路径。为了获得准确的裂纹三维形态及尺寸信息,采用计算机断层扫描(Computed tomography,CT)技术对试验件进行扫描,并对其断层图像进行对比度增强、离群滤噪等图像处理。从图像处理效果来看,离群滤噪方法对于试件结构较为简单,而内部裂纹信息分布相对连续的断层图像处理效果较为理想,且可通过调整其滤噪半径来获得更为清晰的裂纹图像。采用Matlab软件对处理后的断层图像进行三维重建,获得了裂纹的三维可视化图像及其尺寸信息,与裂纹实际情况吻合良好。

The fatigue test about a 2A12 Al alloy bar with an annular notch under complex stress state gave the mechanism of the crack initiation and propagation of the material. And the result shows that the short crack only generated with the second-phase particle detachment from the matrix under complex stress condition when the fatigue cycle is sufficient. The crack slid along the slip band of the grains and presented as a zigzag path of crystallography crack. Industrial computed tomography technique is used to get more useful three dimensional information about the shape and size of the crack. Then the tomographic image is handled with image processing like contrast enhancement and outliers remove. From the perspective of image processing effect, outliers remove is a relatively ideal handling method for specimens with simple structure and continuous crack information. Adjustment of denoising radius could obtain more clearly crack sections. The processed image is reconstructed for three dimensional with the software of Matlab, and the 3D visualization of the crack agrees well with the real crack size.