Hurley Ryan C, Shahin Ghassan, Kuwik Brett S, Lee Kwangmin
Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218.
Hopkins Extreme Materials Institute, Johns Hopkins University, Baltimore, MD 21218.
Proc Natl Acad Sci U S A. 2023 Aug 8;120(32):e2301607120. doi: 10.1073/pnas.2301607120. Epub 2023 Jul 31.
Critical state and continuum plasticity theories have been used in research and engineering practice in soil and rock mechanics for decades. These theories rely on postulated relationships between material stresses and strains. Some classical postulates include coaxiality between stress and strain rates, stress-dilatancy relationships, and kinematic assumptions in shear bands. Although numerical and experimental data have quantified the strains and grain kinematics in such experiments, little data quantifying grain stresses are available. Here, we report the first-known grain stress and local strain measurements in triaxial compression tests on synthetic quartz sands using synchrotron X-ray tomography and 3D X-ray diffraction. We use these data to examine the micromechanics of shear banding, with a focus on coaxiality, stress-dilatancy, and kinematics within bands. Our results indicate the following: 1) elevated deviatoric stress, strain, and stress ratios in shear bands throughout experiments; 2) coaxial principal compressive stresses and strains throughout samples; 3) significant contraction along shear bands; 4) vanishing volumetric strain but nonvanishing stress fluctuations throughout samples at all stages of deformation. Our results provide some of the first-known in situ stress and strain measurements able to aid in critically evaluating postulates employed in continuum plasticity and strain localization theories for sands.
临界状态和连续介质塑性理论已在岩土力学的研究和工程实践中应用了数十年。这些理论依赖于假定的材料应力与应变之间的关系。一些经典假设包括应力与应变速率的同轴性、应力剪胀关系以及剪切带中的运动学假设。尽管数值和实验数据已对这类实验中的应变和颗粒运动学进行了量化，但量化颗粒应力的数据却很少。在此，我们报告了首次利用同步加速器X射线断层扫描和三维X射线衍射对合成石英砂进行三轴压缩试验时测得的颗粒应力和局部应变。我们利用这些数据来研究剪切带的细观力学，重点关注带内的同轴性、应力剪胀和运动学。我们的结果表明：1）在整个实验过程中，剪切带内的偏应力、应变和应力比升高；2）整个样品中主压应力和应变同轴；3）沿剪切带显著收缩；4）在变形的所有阶段，整个样品的体积应变消失但应力波动不消失。我们的结果提供了一些首次测得的原位应力和应变数据，有助于严格评估连续介质塑性和砂土应变局部化理论中所采用的假设。
