Abstract
We numerically study the impact-induced hardening in dense suspensions. We employ the lattice Boltzmann method and perform simulations of dense suspensions under impacts, which incorporate the contact between suspended particles with the free surface of the suspension. Our simulation for a free-falling impactor on a dense suspension reproduces experimental results, where rebound takes place for frictional particles at high-speed impact and high volume fraction shortly after the impact before subsequently sinking. We found that the shear stress of the suspension is not affected by the impact, which clearly distinguishes the impact-induced hardening from the discontinuous shear thickening. Instead, we found the existence of a localized region with distinctively high value of normal stress corresponding to the dynamically jammed region. Our simulation indicates that the frictional interaction between suspended particles is important for the impact-induced hardening to maintain the dynamically jammed region. Furthermore, persistent homology analysis successfully elucidates the topological structure of force chains.
Highlights
A dense suspension can behave as a fluid or a solid depending on the situation
We present the persistent homology analysis to capture the topological structure of force chains
We simulated the impact-induced hardening of suspensions by the lattice Boltzmann method (LBM) simulation with free surface, where the free-falling impactor rebounds for high impact speed with the suspension of high volume fraction involving frictional particles
Summary
A dense suspension can behave as a fluid or a solid depending on the situation. One of the examples of this non-Newtonian behavior is that a running person can stay afloat on top of the suspensions, while a walking person sinks. Waitukaitis and Jaeger discovered a dynamically jammed region which is like a solid plug beneath the impactor [3]. They proposed an added mass effect to explain the solidification induced by the impact. By using a high-speed ultrasound imaging, Han et al measured the sound speed and visualized the flow field of the suspension [5] Their measurement of the sound speed showed no increase in local volume fraction. They suggested that the mechanism behind such solidification in dense suspensions under impact is related to the jamming by shear, instead of densification. The impactinduced hardening can be characterized by dropping an impactor into a dense suspension [9]
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