拉伸荷载作用下含预制裂纹平板试样表面特征量演化规律研究

Evolution of the characteristic variables of plate specimens with prefabricated cracks under tension loads

为探究均匀性和非均匀性试样在拉伸荷载作用下,试样破坏前相关变量场演化特征,采用数字散斑相关方法,对比分析含双边预制裂纹的有机玻璃试样和砂浆试样在拉伸荷载作用下表面图像灰度相关性系数场和y方向应变场及其特征量的演化特征。结果表明:试样表面特征量与试样局部化在时间和空间都存在对应关系;图像灰度相关性系数场演化特征能反映试样变形局部化区域,其特征量演化特征能反映试样均匀变形阶段和非均匀变形阶段,在非均匀变形阶段,应变局部化"竞争"激烈,图像灰度相关性系数特征量随时间波动较大,整体上呈急剧增加趋势,可以作为含双边预制裂纹试样破坏前的征兆;y方向应变场演化特征反映了试样应变局部化区域和"竞争"位置以及裂纹起裂位置,其特征量演化特征与载荷随时间变化相关,试样的非均匀性造成特征量处于不断的波动状态,可以区分均匀性试样与非均匀性试样。

In order to investigate the evolution characteristics of relevant variable fields of uniform and non-uniform specimens under tensile loads,the correlation coefficient field of image gray,the strain field in y-direction and their characteristic variables of PMMA and mortar specimens with bilateral prefabricated cracks under tension loads were analyzed and compared using the digital speckle correlation method. The results show that there exist temporal and spatial corresponding relations between the surface characteristic variable and the localization of specimens. The evolution characteristics of the correlation coefficient field of the image gray can reflect the deformation localization area of the specimen,and the uniform and non-uniform deformation stages can be distinguished by the evolution of the characteristics variable of the correlation coefficient. In the non-uniform deformation stage where strain localization‘competes’ intensely,the characteristics variable of the gray correlation coefficient of images fluctuates with time and increases sharply on the whole,which signifies the failure precursor of the specimen with bilateral prefabricated cracks. The evolution characteristics of the strain field in y-direction can reflect the strain localization area,and the positions of strain localization‘competition’and crack initiation. The evolution process of the characteristic variable of the strain field in y-direction is related to the change of the load over time,and the heterogeneity of the specimen results in continuous fluctuation of the characteristic variable,which can be used to distinguish homogeneity and heterogeneity specimens.