Effects of Fluid Viscosity on Wave Propagation Through Submerged Granular Media

摘要

Wave propagation through dry granular media has been extensively studied both numerically and experimentally in the past, however, wave dynamics of wet granular materials have not received adequate attention. The cohesion at inter-particle contacts, largely ignored in dry macroscopic granular materials, plays a major role in mechanics of wet granular materials. In this study, a drop-tower based experimental setup was developed to investigate wave propagation through the 2D assembly of cylindrical particles immersed in optically transparent fluids. These granular assemblies, consisting of polyurethane cylinders arranged into two different configurations - cubic and hexagonal, can be subjected to low-speed impact loading up to a projectile velocity of about 6 m/s. The deformation of individual particles in the granular assemblies can be recorded using a high-speed camera and the kinematics and the strain fields on each speckle-patterned particle can be calculated by digital image correlation (DIC). Moreover, an electrodynamic shaker can also be coupled with the aforementioned fixture and the influence of liquid viscosity on the low-amplitude vibrational response of the immersed granular crystals can be quantified using a scanning vibrometer. The wave dynamics of granular crystals immersed in fluids with varying levels of viscosity were investigated using the impact loading using the drop-tower setup and the scanning vibrometer based vibrational measurements. In order to quantify the effect of single or multiple defects on wave propagation, the impact response of dry and immersed granular crystals with different types of defects (size, stiffness or both) was also investigated.