SGER: Experimental Investigation of Stress Rotation Effects in Soils

在大的应力逆转和建模交叉各向异性的土壤行为的建模过程中，在过去已经做了模型制定的应力不变量，并结合各向同性和旋转运动硬化的组合。这种技术似乎捕捉三轴压缩和立方三轴试验中观察到的土壤行为具有良好的精度。然而，将扭转剪切试验中的大应力反向过程中的测量行为纳入运动硬化模型已被证明是有问题的。事实上，尝试在旋转运动学模型中包括应力旋转效应已经阐明了为什么这种类型的模型不能捕获土壤行为的所有方面，以及为什么运动硬化模型背后的概念，无论是平移还是旋转，都不能正确预测一般应力条件下的土壤行为，如有限元或有限差分设置所需。 在实验研究中，将研究颗粒材料在纯应力旋转过程中的行为。这种情况将突出现有的各向同性和随动硬化模型的缺点。该研究将主要用于（a）证明现有本构模型的缺点，（B）评估缺失的塑性应变的大小，从而评估本构模型局限性的严重程度，（c）启动数据收集，这将指示新的建模工作的方向，以正确捕获缺失的预测应力旋转效应的能力，以及（d）根据本文提出的探索性实验结果制定更广泛的实验计划。应力旋转扭转剪切试验的实验结果将证明和突出目前现有的各向同性和运动硬化本构模型的局限性。这些局限性包括他们未能正确地预测土壤的行为在大多数情况下，发生在现实的边界值问题，他们据称是开发。这项工作将有更广泛的影响，新的努力将即将更新或重新制定本构模型，将能够包括应力旋转的影响。因此，拟议的研究将对本构建模的未来产生重大影响，它将影响有限元和FDM计算的边界值问题，涉及工程材料。

Modeling soil behavior during large stress reversals and modeling cross-anisotropic soil behavior have been done in the past by models formulated in terms of stress invariants and incorporating combinations of isotropic and rotational kinematic hardening. This technique seems to capture the soil behavior observed in triaxial compression and cubical triaxial tests with good accuracy. However, incorporation of measured behavior during large stress reversals in torsion shear tests into the kinematic hardening model has proved to be problematic. In fact, the attempt to include effects of stress rotation in the rotational kinematic model has illuminated why this type of model does not capture all aspects of soil behavior, and why the concepts behind the kinematic hardening models, whether translational or rotational, will not be able to correctly predict soil behavior under general stress conditions, as required in a finite element or finite difference setting. In the experimental investigation, the behavior of granular materials during pure stress rotation will be studied. This condition will highlight the shortcomings of existing isotropic and kinematic hardening models. The research will primarily be performed to (a) demonstrate the shortcoming of existing constitutive models, (b) evaluate the magnitude of the missing plastic strains and consequently the severity of the limitations of the constitutive models, (c) initiate data collection that will indicate the direction of new modeling efforts required to capture the missing capability of predicting effects of stress rotation correctly, and (d) formulate a plan for a more extensive experimental program on the basis of the findings from the exploratory experiments proposed here.Experimental results from torsion shear tests with stress rotation will demonstrate and highlight the extent of the limitations of currently existing isotropic, as well as kinematic hardening constitutive models. These limitations consist of their failure to predict soil behavior correctly in most situations that occur in realistic boundary value problems, and for which they purportedly were developed. This work will have the broader impact that renewed efforts will be forthcoming to update or reformulate constitutive models that will be able to include the effects of stress rotation. The proposed research will therefore have major impact on the future of constitutive modeling and it will impact the FEM and the FDM calculations of boundary value problems involving engineering materials.