SGER: Experimental Investigation of Stress Rotation Effects in Soils

在过去，模拟土体在大应力反转时的行为和模拟交叉各向异性的土体行为都是根据应力不变量并结合各向同性和旋转运动硬化的组合而建立的。这项技术似乎捕捉到了在三轴压缩和立方体三轴试验中观察到的土的特性，并具有很好的准确性。然而，将扭剪试验中大应力反转时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，在旋转运动学模型中包含应力旋转效应的尝试说明了为什么这种类型的模型不能涵盖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，都不能正确地预测在一般应力条件下的土壤行为，正如有限元或有限差分设置所要求的那样。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。这一条件将突出现有各向同性和运动强化模型的缺点。这项研究的主要目的是：(A)证明现有本构模型的缺陷，(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性，(C)启动数据收集，以指出正确预测应力旋转影响的缺失能力所需的新建模工作的方向，以及(D)根据这里提出的探索性实验的结果，制定更广泛的实验计划。应力旋转扭剪试验的实验结果将展示和突出现有各向同性本构模型以及运动硬化本构模型的局限性。这些局限性包括它们在大多数情况下未能正确地预测土壤行为，这些情况发生在现实的边值问题中，据说它们是为这些问题而开发的。这项工作将产生更广泛的影响，即将重新努力更新或重新制定能够包括应力旋转影响的本构模型。因此，所提出的研究将对本构模型的未来产生重大影响，并将影响涉及工程材料的边值问题的有限元和有限差分计算。

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.