A jammed state is a common phenomenon in complex granular systems, in which the relationship between the mechanical properties and the geometric structures is very complicated. The critical jammed state in a two-dimensional particle system is studied by numerical simulation. The system is composed of 2050 particles with two different radii, whose distribution is random. Initially the particles with a smaller radius are of a looser distribution in the given space. When the radius increases, a transition from the looser state to the jammed state happens. The particle dimension-radius ratio and the percentage of large particles kB play primary roles in this system, which are discussed in detail based on the statistical analysis of the average contact number, packing fraction, and contact type. By analyzing the relationship between pressure and packing fraction of the granular system, the critical jammed point for the applied pressure to the boundary can be found. Numerical simulation result shows that no obvious connection exists between the average contact number and the percentage of large particles for the case that the particle dimension-radius ratio is less than 1.4. The average contact number approximate to 4 when = 1.4, which is consistent with previous conclusions. The average contact number first decreases and then increases when the percentage of large particles become larger in the case 1.4. A minimum value C = 0.84 is obtained when kB = 0.5. When the percentage of large particles increases, the critical packing fraction decreases first and then increases in the case 1.8, but it almost keeps constant for 1.8. When the percentage of large particles is close to either 0% or 100%, the granular system is approximately mono-disperse. In this case, the average contact number and packing fraction become constant. When the percentage is close to 50%, the critical average contact number decreases all the time with larger particles-radius ratio, while the critical packing fraction decreases first and then increases. The percentage of large-small contact type is also discussed. The value varies following a quadratic function with the increase of the percentage of large particles, while the particles-radius ratio has slight impact on this variation. Specifically, we have calculated the percentage of large-small contact type based on probabilistic method, and the result agrees well with the simulation results. We give the reason why previous researchers studied the case of = 1.4 :1 and kB = 0.5 on the basis of results in this paper, and find that the values of and kB have no influence on the power-law relation around the critical jammed state.
Granular material is a kind of soft condensed matter, which gathers up a large number of particles, and the relation between its microstructure and macroscopic mechanical properties is very complex. In this paper, the lateral stress distribution of the two-dimensional vertically stacked lattice of granular material under a pressure in the vertical direction has been investigated experimentally. The steering behavior of the vertical pressure in a granular system is discussed and analyzed in detail based on the experimental results. Results show that in the process of slow compression, the vertical pressure increases slowly in a nonlinear form at first and gradually transforms into a linear increase. This phenomenon corresponds to the dynamic processes of friction-slip-extrusion. This kind of behavior is more significant in the particle system of the same size. In the initial stage of pressing, the vertical force of the stepping motor is mainly used to overcome the friction between the particles and the sliding friction between the particle and the wall. As the friction in the granular system is related to the geometry of the particulate deposits, the material of particles, the roughness of the wall surface, and other relevant factors, the front-end of vertical pressure displays nonlinear characteristics. Continuing the squeeze and push forward, a force chain is formed among particles through self-organization. The vertical force is mainly used to overcome the elastic pressing force between the particles and the force to the wall, so later on the vertical pressure performs linear growth. For the system of particles with an established packed structure, the vertical pressure applied in the vertical direction steers along the force chain between the particles, and the value of horizontal pressure is different at different stacking heights. That is, the pressure in the middle is greater than that at the top and the bottom. The saturated value of steering coefficient k decreases with the stacking angle θ. As the stacking angle increases, the vertical component of the stress becomes more pronounced than its horizontal component. The expression of steering coefficients against stacking angle has been obtained through careful analysis of the geometrical structure and the force distribution of the granular pile, and the theoretical value fit well with the experimental results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.