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基于亚像素角点检测的数字图像测量系统能够记录三轴试样表面方块角点的位移,从而获得试样表面每一时刻的局部应变及应变场。分析了试样不同位置的局部径向应变在剪切过程中的变化,获得了以不同初始成样含水率制备的松砂和密砂试样在不同特征时刻的应力与应变的特征值。通过轴向应变场的变化分析了从应变局部化出现到剪切带发育、形成的这一完整的渐进破坏过程,总结了剪切带形成时的局部最大轴向应变特征值,并定性地分析了剪切带内、外土体在渐进破坏过程中不同的轴向应变增长率。试验结果表明:在应变场中试样应变局部化明显,并可以依此确定应变局部化的出现、剪切带的形成;对于密砂及初始含水率为0%制备的松砂试样,应力在应变局部化出现之初即达到峰值,剪切带形成时应力已经开始下降,进入应变软化阶段;以初始含水率为6%和12%制备的松砂试样在达到应力峰值时剪切带已经形成;剪切带内土体的局部轴向应变增长幅度比剪切带外的土体大得多。试样整体轴向应变的增大主要是由剪切带内土体剪切破坏产生的较大轴向应变所致。
The digital image measuring system based on the sub-pixel corner detection can record the displacement of square corners of the triaxial specimen surface to obtain the local strain and strain field at every moment of the specimen surface. The variation of local radial strain at different positions of the specimen during the shearing process was analyzed. The characteristic values of stress and strain at different characteristic moments of sand and sand samples prepared with different initial sample-forming water contents were obtained. Through the analysis of the axial strain field, the complete asymptotic failure process from the occurrence of strain localization to the development and formation of shear zone is analyzed, and the local maximum axial strain eigenvalue of shear zone formation is summarized and analyzed qualitatively In the shear zone, the growth rates of different axial strains in the inner and outer soil during progressive failure are also presented. The experimental results show that the strain localization is obvious in the strain field and the occurrence of strain localization and shear band formation can be determined accordingly. For the sand and the loose sand sample with initial moisture content of 0%, the stress At the beginning of strain localization, the peak value is reached. The stress has begun to decrease when the shear band is formed, and enters into the strain softening stage. When the initial moisture content is 6% and 12% Has been formed; within the shear zone, the local axial strain of soil increases more than the soil outside the shear band. The overall axial strain increase of the specimen is mainly caused by the larger axial strain caused by soil shear failure in the shear zone.