A review of basic snow mechanics
A review of basic snow mechanics
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发表时间：
2007
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通讯作者：
M. Mellor
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作者：
M. Mellor
在导言部分的主题是定义，确定研究目标，概述了雪力学的历史观点，并规定了理论分析的要求，本构方程和失效准则的形式。一节变形打开审查理想化的流变学无损加载，给出一般微分方程和相关的特殊解决方案的一维模型。简单的弹性性能，来自准静态和动态试验的雪，总结，并考虑率，频率，密度，温度等的影响。粘弹性性质以复模量、蠕变瞬变粘度、损耗因子等来描述，并且考虑了诸如温度、密度和频率的独立变量。在持续蠕变的粘性行为进行了介绍，并在介绍单轴应力和单轴应变的测量所获得的数据，强调表征的并发症。简单的应力分析介绍，以方便进一步讨论，所涵盖的点包括分离的应力和应变张量成偏和反分量，应力和应变不变量的定义，剪切和体积粘度，粘性类似的泊松比，并确定应力分量的平衡方程。讨论了体积应变和不可逆压缩性，并提出了“状态方程”表征。单轴应力状态下的压力/密度数据进行了编译，并开发了各种速率和温度条件下的体积应力对比容的曲线图。偏应力/应变率关系的条件下，可以忽略不计的体积应变率被认为是，借鉴来自非常规来源的数据，包括单轴抗压强度试验和蠕变剖面解决雪坡。本节最后讨论了制定多轴应力状态的一般本构方程的问题。关于故障的一节从故障、强度和故障标准的讨论开始，特别是当这些术语适用于雪时。在单轴拉伸和压缩强度测量被认为是，和可用的数据进行汇编。考虑了剪切强度的定义，讨论了雪的c-0表征的优点和局限性，并编制了一些更可靠的剪切强度数据。物理和统计故障理论的基础上，结构缺陷的概念，雪的强度和孔隙度之间的经验关系进行了描述，并介绍了导出0和孔隙度之间的关系的可能性。尝试发展的现象学故障标准雪简要提及。一个警告注意不连续的崩溃的雪在压缩，任意强度指标与基本强度性能的相关性进行了讨论。强度和弹性模量的相关性进行了探讨，作为一种可能的方法，估计强度的无损原位测试。关于边界摩擦的一节介绍了与粘性雪表面的动摩擦有关的物理理论，并总结了实验结果，这些实验结果给出了动摩擦随接触压力、接触区域尺寸、滑动速度、环境温度和滑块材料的变化。静摩擦力和粘附力的区别和讨论，并建议测量或估计真正的静摩擦力的方法。本文考虑了流态化雪的边界摩擦，并在探索性计算中处理了在扩散良好的湍流边界层中由惯性效应引起的阻力。最后，对雪力学研究中的主要难点进行了评价，并对今后的研究方向提出了建议。
In an introductory section the subject is defined, research goals are identified, a historical perspective of snow mechanics is outlined, and requirements for theoretical analysis, in the form of constitutive equations and failure criteria, are specified. A section on deformation opens with a review of idealized rheology for nondestructive loading, giving general differential equations and pertinent special solutions for one-dimensional models. Simple elastic properties, as derived from quasistatic and dynamic tests on snow, are summarized, and effects of rate, frequency, density, temperature, etc. are considered. Viscoelastic properties are described in terms of complex moduli, viscosity for creep transients, loss factor, etc., and independent variables such as temperature, density and frequency are taken into consideration. Viscous behaviour in sustained creep is introduced, and complications of characterization are emphasized during presentation of data obtained by measurements involving uniaxial stress and uniaxial strain. Simple stress analysis is introduced to facilitate further discussion; points covered include separation of stress and strain tensors into deviatoric and dilatational components, definition of stress and strain invariants, shear and bulk viscosities, viscous analogue of Poisson's ratio, and determination of stress components from equilibrium equations. Volumetric strain and irreversible compressibility are discussed, and 'equation of state' characterization is proposed. Pressure/density data for uniaxial stress states are compiled, and a plot of bulk stress against specific volume is developed for various rates and temperature conditions. Deviatoric stress/strain-rate relations for conditions of negligible volumetric strain rate are considered, drawing on data derived from unconventional sources, including uniaxial compression strength tests and creep profiles for settled snow slopes. The section closes with a discussion of the problem of formulating general constitutive equations for multiaxial stress states. A section on failure starts with discussion of failure, strength, and failure criteria, especially as the terms apply to snow. Strength measurements in uniaxial tension and compression are considered, and available data are compiled. Definition of shear strength is considered, the merits and limitations of c—0 characterization of snow are discussed, and some of the more reliable shear strength data are compiled. Physical and statistical failure theories based on structural defect concepts are mentioned, empirical relationships between the strength of snow and its porosity are described, and the possibility of deriving a relation between 0 and porosity is introduced. Attempts to develop phenomenological failure criteria for snow are mentioned briefly. A cautionary note on discontinuous collapse of snow under compression is included, and correlation of arbitrary strength indices with basic strength properties is discussed. Correlation of strength and elastic modulus is explored as a possible method for estimating strength from nondestructive in situ tests. A section on boundary friction introduces the physical theory relating to kinetic friction of coherent snow surfaces, and summarizes experimental findings that give variations of kinetic friction with contact pressure, dimensions of contact areas, sliding speed, ambient temperature, and slider materials. Static friction and adhesion are distinguished and discussed, and methods for measuring or estimating true static friction are suggested. Boundary friction of fluidized snow is considered, and drag induced by inertial effects in a well-diffused turbulent boundary layer is treated in an exploratory calculation. The review concludes with an appraisal of the major difficulties in snow mechanics and with some suggestions for research direction.