Abstract This work focuses on the behaviour of granular materials under unsteady, simple shear conditions and, in particular, on from solid- to fluid-like phase transition. The authors introduce a theoretical model, based on continuum mechanics, able of predicting the mechanical behaviour of granular media under both quasi-static and dynamic conditions. The model assumes a parallel scheme where confining and shear stresses are computed as the sum of two contributions: the quasi-static and the collisional one. The quasi-static contribution is obtained by employing an elastic–plastic model including the critical state concept, while the collisional one is derived from the kinetic theory of granular gases. In order to test the model under unsteady conditions, DEM numerical simulations of time evolving homogeneous shear flows have been performed by considering an assembly of frictional, deformable spheres, under constant volume conditions. Simulations have been performed by systematically changing both void ratio and shear rate. The comparison between theoretical model predictions and DEM results is done in terms of time evolution of stresses and granular temperature. Suitable initial conditions are imposed to reproduce both solid to fluid (liquefaction) and fluid to solid (solidification) phase transitions.

中文翻译：

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模拟颗粒材料的相变：从不连续体到连续体

摘要 这项工作的重点是在不稳定的简单剪切条件下颗粒材料的行为，特别是从固体到类流体的相变。作者介绍了一种基于连续介质力学的理论模型，该模型能够预测准静态和动态条件下颗粒介质的机械行为。该模型假设一种并行方案，其中围压和剪应力计算为两个贡献的总和：准静态和碰撞贡献。准静态贡献是通过采用包含临界状态概念的弹塑性模型获得的，而碰撞模型则来自颗粒气体的动力学理论。为了在非稳态条件下测试模型，在恒定体积条件下，通过考虑摩擦、可变形球体的组件，已经执行了随时间演变的均匀剪切流的 DEM 数值模拟。通过系统地改变空隙比和剪切速率来进行模拟。理论模型预测和 DEM 结果之间的比较是在应力和颗粒温度的时间演变方面进行的。施加合适的初始条件以再现固体到流体（液化）和流体到固体（凝固）的相变。理论模型预测和 DEM 结果之间的比较是在应力和颗粒温度的时间演变方面进行的。施加合适的初始条件以再现固体到流体（液化）和流体到固体（凝固）的相变。理论模型预测和 DEM 结果之间的比较是在应力和颗粒温度的时间演变方面进行的。施加合适的初始条件以再现固体到流体（液化）和流体到固体（凝固）的相变。