Computational Modeling of Strain Localization in Frictional Granular Materials

这项研究项目涉及与颗粒材料的变形和破坏有关的基本过程；具体地说，应变局部化，以及它在地震引起的地面破坏中所起的作用。实验观察表明，应变局部化是地面破坏机制的一个组成部分，即使在由于强烈地面震动而液化的土壤中也是如此。我们的目标是在现有实验数据的基础上将其量化，以便开发一个基于微观力学的统一计算本构模型来分析和量化实验观测。该模型广泛应用于颗粒材料中的许多问题，特别是地震中的地面破坏问题。该程序通过以下步骤建立了一个基于科学的计算模型：1.从微观尺度和颗粒之间的相互作用入手，明确地将组构及其演化与宏观背应力及其演化联系起来。基于颗粒与颗粒的接触力和接触法向分布密度函数(表征织物的特性)，得到光弹实验中观察到并定量记录的抗胀剪阻力的显式表达式。在细观膨胀滑移模型的基础上，建立了仅涉及少量明确本构参数的显式本构关系。利用现有的大量实验数据库，将本构参数与试验数据进行关联。开发基于塑性预报器-弹性校正器概念的计算算法。利用DYNA3D中的本构算法，对剪切带试验结果进行了量化。这也将验证该模型应用于其他问题的有效性。

This research project addresses fundamental processes associated with the deformation and failure of granular materials; specifically strain localization, and the role that it plays in earthquake-induced ground failures. Experimental observations suggest that strain localization is an integral part of the ground failure mechanism, even in soil that has liquefied as result of strong ground shaking. The goal is to quantify this, based on existing experimental data, in order to develop a micromechanically-based unified computational constitutive model to analyze and quantify experimental observations. The model has broad application to many problems in granular materials, in particular to ground failure in earthquakes.The program involves the creation of a science-based computational model through the following steps:1. Starting with the micro-scale and grain-to-grain interaction, toexplicitly relate fabric and its evolution to macroscopic backstress and its evolution.2. Based on grain-to-grain contact forces and the distribution density function of the contact normals (which characterizes the fabric), obtain explicit expressions for the resistance to the dilatant shearing observed and quantitatively documented in photoelasic experiments.3. Based on the dilatant sliding model at the meso-scale, develop explicit constitutive relations involving just a few well-defined constitutive parameters.4. Using an existing extensive experimental database, relate the constitutive parameters to test data.5. Develop computational algorithms based on the plastic predictor-elastic corrector concept.6. Using the constitutive algorithm in DYNA3D, quantify experimental results on shearbanding. This also will verify the effectiveness of the model for application to other problems.