雪高应变率变形的离散元模型
Discrete element model for high strain rate deformations of snow
摘要：
在工程应用中，雪经常经历大而快的变形。在这些变形过程中，雪从烧结的多孔材料转变成颗粒状材料。为了捕捉这个过程的基本力学行为的离散元（DE）模型是物理上最合适的。它明确地包括所有相关的组成部分：雪的微观结构，包括粘结颗粒，键的断裂和随后的重排和松散颗粒的相互作用。我们开发和校准的DE雪模型的基础上开放源代码DE代码liggghts。在模型中，雪粒是由随机分布的弹性球连接的弹性-脆性债券。这种粘结结构相当于烧结雪。在施加外力后，键中的应力可能超过其强度，键断裂，我们得到松散的颗粒，对应于粒状雪。模型参数可分为与温度相关的材料参数和与雪型相关的微观结构参数。该模型进行了标定的休止角实验和几个高应变率的机械测试，在一个寒冷的实验室进行。我们证明了DE雪模型的性能，通过模拟不同雪类型的大应变的压缩和剪切变形的组合。该模型成功地再现了实验。该模型能够反映雪的力学特性，如断裂特性、高密度雪与低密度雪的差异、颗粒状切变流或低密度雪的致密化等。该模型是有前途的模拟任意高应变率过程的广泛的雪类型，因此似乎是有用的，适用于不同的雪工程问题。
英文摘要：
In engineering applications snow often undergoes large and fast deformations. During these deformations the snow transforms from a sintered porous material into a granular material. In order to capture the fundamental mechanical behavior of this process a discrete element (DE) model is the physically most appropriate. It explicitly includes all the relevant components: the snow microstructure, consisting of bonded grains, the breaking of the bonds and the following rearrangement and interaction of the loose grains. We developed and calibrated a DE snow model based on the open source DE code liggghts. In the model snow grains are represented by randomly distributed elastic spheres connected by elastic-brittle bonds. This bonded structure corresponds to sintered snow. After applying external forces, the stresses in the bonds might exceed their strength, the bonds break, and we obtain loose particles, corresponding to granular snow. Model parameters can be divided into temperature dependent material parameters and snow type dependent microstructure parameters. The model was calibrated by angle of repose experiments and several high strain rate mechanical tests, performed in a cold laboratory. We demonstrate the performance of the DE snow model by the simulation of a combined compression and shear deformation of different snow types with large strains. The model successfully reproduces the experiments. Most characteristics of the mechanical snow behavior are captured by the model, like the fracture behavior, the differences between low and high density snow, the granular shear flow or the densification of low density snow. The model is promising to simulate arbitrary high strain rate processes for a wide range of snow types, and thus seems useful to be applied to different snow engineering problems.
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