基于CT技术和灰度共生矩阵理论研究不同荷载#br# 作用下混凝土的细观损伤演化过程

混凝土CT试验可以通过CT图像记录外部荷载作用下混凝土内部细观损伤演化信息。峰值强度前不同应力阶段同一断面的CT图像所对应的原始数字矩阵中存在细微差异，而这些不能被直观观察到的细微差异正是研究混凝土损伤萌生、演化的关键。为了深度挖掘数字矩阵中的细微差异信息，文章建立了一套基于灰度共生矩阵理论的分析程序来研究混凝土细观损伤演化过程，并分别应用混凝土试件在单轴静力压缩和拉伸荷载作用下的CT试验结果来验证该方法的有效性。结果表明，该方法不仅能有效地评估混凝土试件的初始细观损伤分布及其在荷载作用下的演化过程，预测试件的断裂位置，确定最大损伤断面，而且能通过统计特征值建立细观损伤变量表达式来定量表征细观损伤。不同应力阶段的4个统计特征值(对比度、能量、相关性、同质性)的变化显示静压试件在应力达到峰值强度的96.2%时，试件内部第42-235幅混凝土横断面位置处损伤有明显发育，且这与试件破坏后的裂缝位置一致，静拉试件在峰值强度前其内部细观损伤未见发育，试件破坏后裂缝出现在89-116幅混凝土横断面CT图像之间。另外，混凝土试件破坏前后的CT图像的灰度共生矩阵对应的彩色热图的对角线分布、峰值个数及带宽与细观损伤发育程度相关。

Coupled X-ray computed tomography and grey level co-occurrence matrices theory#br# as a method for detecting microscopic damage of concrete under different loads

The internal meso-scale damage evolution information of concrete under external load can be recorded by CT images. Subtle differences exist in the original digital matrix corresponding to the CT images of the same section at different stress stages before the peak strength. The subtle differences are the key to study the meso-scale damage initiation and evolution of concrete material,however,such differences cannot be intuitively observed with the naked eye in CT imagesIn this study,to dig out the subtle difference information and investigate meso-scale damage evolution process of concrete,a procedure based on the theory of grey level co-occurrence matrices was established,and the effectiveness of this procedure was verified by the CT test results of statically uniaxial compression and tension of concrete specimens. Results shown that this method not only can evaluate the distribution of initial meso-scale damage and the process of meso-scale damage evolution,predict the fracture position of the specimen,and determine the maximum meso-damage section,but it can also establish the quantitative relationship between statistical characteristic value and meso-scale damage. The changes of the four statistical characteristic values (contrast,energy,correlation,and homogeneity) at different stress stages shown that the meso-scale damage has a considerable development between the 42th and 235th cross-sectional CT image when the stress reaches to 96.2% of the peak strength in the specimen subjected to statically compressive load,and the cracks appear in this area after specimen failure. Before peak load,meso-scale damage cannot be found in the statically tensile specimen,and cracks appear between the 89th and 116th cross-sectional CT images after the peak load. In addition,the GLCM of the CT images was illustrated as colored heatmaps. The changes of diagonal distribution,peak number,and bandwidth in the colored heatmap can reflect the intensity of the gray distribution and the degree of damage.