颗粒物质剪切流动的类固-液转化特性及相变图的建立

颗粒物质类固-液相态间的转化现象广泛存在于工程地质、自然环境和工业生产等诸多领域,其力学特性在相态转化过程中会发生很大的变化,是目前颗粒物质力学研究的热点和难点.通过对颗粒物质类固-液转化过程中基本力学行为的研究,可建立表征颗粒物质类固-液转化的相变图,揭示类固-液转化的内在机理.颗粒物质的类固-液转化过程可大体分为两种,即阻塞与流动状态的转化,以及在流动过程中类固态与类液态力学行为的转化.本文以周期边界条件下的多分散颗粒系统为研究对象,采用离散单元方法数值模拟了单剪流动过程;分析了在不同体积分数和剪切速率下颗粒系统的平均应力、配位数、净接触时间数、有效摩擦系数、惯性指数和广义Savage数等宏观参数的分布规律;讨论了类固-液转化的内在机理,建立了一个以孔隙率、无量纲剪切应力和无量纲剪切速率为基本变量的相变图.该相变图不仅能够表征出颗粒物质由阻塞向流动状态的转变,同时也能够描述颗粒物质在剪切流动中发生类固-液转化的演化规律.

Characteristics in quasi-solid-liquid phase transition of granular shear flow and its phase diagram

The quasi-solid-liquid phase transition of granular materials exists wildly in the fields of engineering geology,nature environments and industry production,etc.The mechanical properties of granular system are quite different during the phase transition,which has been the hot and difficult problem in granular mechanics recently.With the mechanical behaviors investigation of granular quasi-solid-liquid transition,the phase diagram can be established to determine the transition conditions and to understand the transition mechanism.The quasi-solid-liquid phase transition can be divided in the two kinds following.The one is the transition between jamming and unjamming,and the other one is the transition between solid phase and liquid phase under flow conditions.According to the second phase transition,the simple shear flow of polydispersed granular materials with periodic boundary are simulated numerically with discrete element method（DEM）.The macro parameters,such as averaged stress,coordination number,contact time number,effective friction coefficient,inertia number and generalized Savage number etc.,are discussed to understand the intrinsic mechanism of quasi-solid-liquid phase transition under various volume fractions and shear rates.Finally,the e-τ-B phase transition diagram is established with the three basic parameters of porosity,dimensionless shear rate and macro shear stress.