Laboratory and Numerical Investigation on the Impact Behavior of Particle-block Systems

關於顆粒-平板系統撞擊行為的實驗和數值研究

Student thesis: Doctoral Thesis

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Award date15 Apr 2024

Abstract

Collision of grains and between grains and walls (or blocks) is encountered in various natural and industrial problems, such as granular flows, sand dunes, and impacts of rock fragments with protective barriers. These collisions may also be encountered in processes of powders and grains in pharmaceutical, chemical engineering, and polymer technology applications, or applications in unconventional reservoir stimulation such as impacts of proppants with the walls of fractured rocks and particle plugging studies. The collision problem of solid objects has also been studied in the context of interaction of landslide with civil engineering structures (such as bridges) as these collisions may influence the stability of engineering systems.

Despite the significant amount of research being conducted on the collision behavior of grain against block systems, most studies have involved engineered materials. In many practical applications, the impactors/grains may have rough textures or shapes which deviate from the grain with perfectly sphere shape. Thus, in this study it was attempted to provide some insights into the collision behavior of grains using a wide range of grain types. It has been attempted to examine the impact problem of grain – block systems encountering natural sand particles in their original form and also in the presence of a laboratory-created soft coating of microparticles, representing simulant saprolitic rock grains. This coating may also find other applications, for example presence of debris/impurities on the surfaces of fragments, which is expected to alter their contact behavior and interaction with protective barriers. Experimental study on the normal coefficient of restitution of grain-block systems in the presence of thick and thin water layers under low-velocity impacts was carried out; (i) impacts in the presence of a thick liquid layer with water thickness similar to that of the grain diameter and (ii) impacts in the presence of thin liquid layer in the form of water droplets.

Different types of analog barriers (blocks) were examined in this study including brittle (granite) and ductile rigid (brass) blocks, and also analog deformable buffering (rubber) and the data were analyzed in terms of the coefficient of restitution and percentage energy loss expressing the energy dissipation during collision. Due to the highly hysteretic behavior of the analog deformable barrier (such as the rubber plate), the results converged between uncoated and coated particles in terms of coefficient of restitution and percentage energy loss during collision. For all the combinations of particles and analog barriers, transformation of the translational (input) kinetic energy into different forms contributed to the dissipation of energy, more prominently for the analog deformable buffering as the deviating angles from the experiments suggested.

Furthermore, the collision of particles and soft-porous analogue block (made of plaster) was investigated and additionally, granitic blocks were used for complementary investigations. We expected that the results from the granite group could be used as a benchmark to study the impact mechanism of the plaster block. The behavior of the impactor-fluid-block systems was dependent on both global morphology of the impactors and surface roughness. Discrete-based (DEM) numerical simulations were carried out to provide further insights into the collision mechanism. The numerical output was applied to observe the development of compression and tension force chain networks and how these involved during and after impact on different base blocks.

Because the rigid concrete wall is an effective measure to mitigate impacts from geo-hazards (such as landslides), the impact tests of different grain types on concrete blocks of varying compressive strength (C25, C50, C75) were also conducted in this study. The results showed that the impact behavior of grain on concrete block varies depending on the grain type and the properties of the concrete block. The rough glass beads exhibited lower COR values in comparison to smooth glass beads. The impact velocity had an effect on the correlation between particle surface roughness and COR value for C25 concrete blocks. As the impact velocity increased, the influence of surface roughness on the COR value diminished. This observation was linked to the comparatively higher porous structure of the concrete block with lower strength.

Systematic laboratory-based investigation on the role of material type on the behavior against impact in terms of coefficient of restitution has been conducted in the study. Material response and micromechanical parameters, as obtained via this advanced laboratory testing, can provide important inputs in numerical simulations and constitutive modeling. In this study, an experimental investigation into the influence of water layer along with particle type and morphology, on the coefficient of restitution of grain-block systems was conducted, i.e.., examining micro-roughness, fluid layer, material’s density. Simulation works on the impact behavior of grain-block systems has been carried out to provide further investigation on the impact mechanism.

    Research areas

  • Impact mechanism, Micromechanics, Coefficient of Restitution, Roughness, Wet surface