基于X-ray CT原位三轴剪切试验的砂土颗粒材料微观动力学

Microscopic dynamics of sand particles based on X-ray computed tomography and in-situ triaxial compression

将X射线断层扫描技术(CT)与原位三轴剪切试验相结合,分析渥太华砂在剪切过程中的微观动力学演化规律.在试验过程中共完成15次X射线扫描,使用图像分割算法进行颗粒分割并使用球谐函数重构颗粒的表面形貌,根据颗粒的多尺度形态指标序列实现整个加载过程中颗粒的准确匹配与追踪,并分析颗粒位移、转动、局部非仿射运动和局部孔隙率等微观动力学和微观结构指标的演化规律.在剪切过程中颗粒体系的竖向位移分布呈现2个锥形区域,颗粒的转动分布出现明显的X型剪切带.用于度量局部塑性变形程度的局部非仿射运动和局部体积分数呈现出较为明显的相关关系,表明颗粒微观动力学与其微观结构之间存在因果关系,局部自由体积较大的地方更易发生塑性变形.

X-ray computed tomography(CT)and in-situ triaxial shear test were combined to analyze the microscopic dynamics evolution of Ottawa sand under triaxial compression.A total of 15 X-ray scans were taken during the experiment.The particles were separated by the image segmentation algorithm and reconstructed by spherical harmonic functions.The particles were matched exactly and tracked during the loading process based on the multi-scale morphological indicators of particles,and the evolution of microscopic dynamics and microscopic structural indicators,such as particle displacement,rotation,local non-affine motion,and local porosity were analyzed.During the shear process,the vertical displacement distribution of the particle system presents two conical regions,and the rotational distribution of the particles exhibits obvious X-shaped shear bands.The local non-affine motion,which was used to measure the local plastic deformation,was significantly correlated with the local volume fraction,suggesting a causal relationship between the microscopic dynamics and particle microstructure,i.e.,plastic deformation was more likely to occur where the local free volume was large.