The influence of temperature on the small-strain viscous deformation mechanics of snow: a comparison with polycrystalline ice
The influence of temperature on the small-strain viscous deformation mechanics of snow: a comparison with polycrystalline ice
复制标题
温度对雪小应变粘性变形力学的影响：与多晶冰的比较
作者：
Carlo Scapozza;P. Bartelt
摘要格伦定律是描述多晶冰粘性变形的常用定律。它是一个幂律，涉及应力粘性应变速率，并包含三个材料参数：n，幂律指数，Q，激活能，和A0，材料常数。由于多晶冰是雪的组成材料，因此可以预期，雪的粘性变形机制与多晶冰的粘性行为有关，特别是在小应变和低应变率下，当冰基质中的运动学效应如键断裂、键形成和颗粒滑动是次要的。基于对密度范围为200- 430 kg m-3、温度范围为-20 ° C至-2 ° C的细粒雪进行的64次变形控制压缩试验，我们表明，格伦定律-材料参数与多晶冰相似-可以用于模拟高密度雪的粘性变形。冰材料参数的值对于高于400 kg m-3的相对低密度的密度有效;它们对于密度低于360 kg m-3的雪无效。我们提出的变化的n，Q和A的雪作为密度和温度的函数。对这种现象的一个可能的解释是，低密度雪中的冰粒受到的约束较少。因此，变形机制，如晶界滑动，增加了整体的重要性，导致较小的n值和较高的激活能，Q。虽然低密度雪的材料行为可以用幂律精确建模，但幂律参数与多晶冰的参数相差很大。n和Q随温度和密度的大变化强调了预测雪崩的困难。
Abstract Glen’s law is commonly used to model the viscous deformation of polycrystalline ice. It is a power law that relates stress to viscous strain rate and contains three material parameters: n, a power-law exponent, Q, an activation energy, and A 0, a material constant. Because polycrystalline ice is the constituent material of snow, it is to be expected that the viscous deformation mechanics of snow are related to the viscous behaviour of polycrystalline ice, especially under small strains and low strain rates when kinematic effects in the ice matrix like bond breakage, bond formation and grain sliding are of secondary importance. Based on 64 deformation-controlled compression tests on fine-grained snow in the density range 200–430kg m–3 and temperature range T = –20 to –2°C, we show that Glen’s law—with material parameters similar to those for polycrystalline ice—can be applied to model the viscous deformation of high-density snow However, the values of the ice material parameters are valid for densities above a relatively low density of 400 kg m–3; they are not valid for snow with densities below 360 kg m–3. We present the variation of n, Q and A for snow as a function of density and temperature. A possible explanation for this behaviour is that the ice grains in low-density snow are less constrained. Therefore, deformation mechanisms, such as grain-boundary sliding, increase in overall importance, leading to smaller n values and higher activation energies, Q. Although the material behaviour of low-density snow can be accurately modelled using a power law, the power-law parameters depart substantially from those of polycrystalline ice. The large variation of n and Q with temperature and density underscores the difficulty of predicting snow avalanches.