剪切振动下湿颗粒的力学谱

Wet granular matter mechanical spectroscopy under low-frequency shear

在恒温25℃剪切振动条件下,测量不同水分含量的NaCl湿颗粒体系的力学谱(能量耗散tanφ和剪切模量G).研究发现,随着剪切振幅增大,NaCl湿颗粒体系的剪切模量G和能量耗散tanφ都表现出类似于干颗粒体系的阻塞(Jamming)转变行为.随着体系中水含量的增大,湿颗粒体系的剪切模量G和能量耗散tanφ在质量分数约等于11%的临界水浓度下均出现一个峰值,且峰位与应变振幅无关,表明此时颗粒之间主要的作用力发生了变化.

Dry granular materials consist of a collection of macroscopic discrete particles interacting solely via contact forces.By changing the external conditions, the granular packing displays rich phenomena ranging from fluid-like properties to jamming glassy behavior and to aging observed when these grains are trapped in a frozen state. Once the grains contact liquid, the force between the liquid and grains has an influence on the mechanical properties of the wet granular materials, and some mechanical behaviors are quite different from those of the dry granular materials. However, the underlying mechanism of the complex dynamics of granular assemblies is still not completely understood.In this paper, mechanical spectroscopy（the shear modular G and the related energy dissipation tan φ） of NaCl wet granular system is investigated with different liquid content（weight fraction） under the constant temperature 25 ℃and air humidity by a modified low-frequency inverted torsion pendulum. The NaCl wet granular system also displays jamming behavior when subjected to an external vibration with increasing intensity, which is quiet similar to dry granular matter. With the increase of water content, all the spectra of tanφ and modular G show a peak at the water content about 11%（critical water content）. At the same time, the applied shear force has little influence on the positions of these peaks. All of these behaviors illustrate that the main interaction forces among granular matters in the system are changed at the moment.