致密颗粒材料的热力学：粒子尺度视角
Thermomechanics of dense granular materials: a particle-scale perspective
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中文总结 AI 辅助
本文从粒子尺度视角提出致密颗粒材料的热力学框架，通过DEM模拟识别组构与结构变量，验证耗散普遍性及弹塑性假设失效，并展示三机制弹塑性模型的拟合与量化方法。
中文摘要 AI 辅助
本文提出了一个用于致密颗粒材料等温率无关本构行为的广义热力学框架。该框架中的基本量可直接在离散元（DEM）模拟中测量：自由能、耗散、应力和应变。本文提出能量和耗散由两组内部变量控制：控制可逆刚度的组构变量和与内部滑动相关的结构变量。通过模拟识别并测量了相关的组构变量。对于结构变量，考虑了两种假设：宏观尺度不可逆应变和滑动接触间微观尺度摩擦力的聚合度量。两种假设均通过模拟进行了测试，模拟允许直接计算内部变量。随后，本文展示了测量变量在增量本构模型中的应用方式。其他发现包括：（1）接触滑动产生的耗散普遍存在，并发生在增量加载的所有方向。（2）应变方向的反转不会导致接触运动的反转，且在加载反向时接触继续滑动。（3）自由能不能假设为光滑可微；相反，必须使用Gâteaux导数来处理不可逆效应。（4）弹塑性的基本假设被违反：不存在纯可逆应变区域，不存在统一屈服方向，不存在统一流动方向，且不可逆应变与投影总应变不成比例。然而，一个三机制弹塑性模型紧密拟合了DEM结果，并展示了量化该模型的方法。结果强调，需要先进的本构模型来捕捉颗粒材料的一般增量行为。
英文摘要
The paper presents a broad thermomechanic framework for the isothermal rate-independent constitutive behavior of dense granular materials. The essential quantities in this framework are directly measurable in discrete element (DEM) simulations: free energy, dissipation, stress, and strain. The paper proposes that energy and dissipation are governed by two sets of internal variables: fabric variables that control the reversible stiffness and structure variables associated with internal sliding. The relevant fabric variables are identified and measured with simulations. Two hypotheses are considered for the structure variables: the macro-scale irreversible strain and an aggregate measure of the micro-scale frictional forces among sliding contacts. Both hypotheses are tested with simulations, which allow direct calculation of the internal variables. The paper then demonstrates the manner in which the measured variables are applied in incremental constitutive models. Among other findings are the following. (1) Dissipation from contact sliding is pervasive and occurs in all directions of incremental loading. (2) Contact motions are not reversed by a reversal of the strain direction, and contacts continue to slide when loading is reversed. (3) The free energy can not be assumed smoothly differentiable; instead, Gâteaux derivatives must be used with irreversible effects. (4) Basic assumptions of elastoplasticity are contravened: no region of purely reversible strain exists, no uniform yield direction exists, no uniform flow direction exists, and irreversible strain is not proportional to the projected total strain. A three-mechanism elastoplasticity model, however, closely fit the DEM results, and methods are demonstrated for quantifying the model. The results emphasize that advanced constitutive models are needed for capturing the general incremental behavior of granular materials.
发表机构
- Donald P. Shiley School of Engr., Univ. of Portland（波特兰大学唐纳德·P·谢利工程学院）
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