Stress wave in monosized bead string with various water contents
Wet granular materials exhibit unique physical and mechanical properties, especially in relation to wave propagation, which is quite different from dry granular materials. In this paper, by introducing the capillary bridge force into the discrete element method, the stress wave in mono-sized bead string with various water content has been studied. First the vibration of two particles with liquid bridge has been analyzed. The presence of the liquid bridge force causes the kinetic response of the particles to exhibit completely different properties than that of the dry particles. The equilibrium position is affected by both the physical properties of the particles and the liquid bridge properties. Then the wave propagation behaviors in a mono-sized bead string have been analyzed. According to whether the liquid bridge volume has an effect on granular motion, the whole process can be divided into two stages. Stage I, particles are physically contacted with each other directly. The influence of liquid bridge force is independent of the bridge volume. Stage II, particles start to oscillate back and forth at their equilibrium positions, the influence of the liquid bridge force becomes related to the bridge volume. The kinetic energy dissipation first decreases and then increases. A U-shaped trend appears throughout the dissipation process. In our work, the mechanical properties of wet granular materials are studied from two levels: particle vibration and wave propagation, which will provide theoretical guidance for the application of granular materials in aqueous environment.
Keywords: Granular material, DEM, Capillary force, Particle vibration, Wave propagation