Abstract:
In order to investigate the relation between friction behavior and granular matter behavior during powder compaction, the process of ferrous powder compaction was simulated based on granular matter mechanics and the discrete element method. The reliability of simulation also was verified by compaction equation. The contact force judgment method was used to extract the force chain information of powder. The quantitative analysis parameters of force chains (the number, direction coefficient, unbalanced coefficient of bearing capacity, and buckling coefficient of force chains) were introduced to analysis the evolution of force chains on the powder system. Furthermore, the influence of tribological characteristics on the quantitative characteristics of force chains was analyzed based on the different friction coefficients between particles, friction coefficients between die wall and particles and the change of particle’ motion condition. The relation between tribological characteristics and evolution of force chains was established. Results showed, the ferrous powder compaction curve obtained by compaction simulation can be fitted by Heckel compaction equation and the simulation model was reliable. With the increase of the friction coefficient between particles, the direction coefficient, unbalanced coefficient of bearing capacity, and buckling coefficient of force chains all increased but the number of force chains became fewer. And the low friction coefficient between particles can affect the force chain and was helpful for powder densification by reducing the movement obstacles between particles. The quantitative characteristics of force chains had insignificant change with the increase of the friction coefficient between die wall and particles. The evolution of quantitative characteristics of force chains at different friction coefficients between die wall and particles only had some differences during specific stage, i.e. the stage of axial strain varied from 0.1 to 0.16. Compared with the friction coefficient between die wall and particles, the friction coefficient between particles had more remarkable influence on the evolution of force chains’ quantitative characteristics. Because the friction coefficient between die wall and particles mainly reflected the external friction conditions, it mainly affected the contact motion behavior of the particles on the side wall and the displacement rearrangement behavior of particles within the system gradually. However, the friction coefficient between particles affected the contact motion state of each powder within the system, and directly affected the displacement rearrangement behavior of particles within the system. Moreover, the change of contact and motion condition of particles had relation with the evolution of force chains’ quantitative characteristics to some degree. The increase of ratio of sliding contact reflected the strengthening of sliding friction behavior. It can lead to the increase of the number of force chains and the decrease of the buckling coefficient of force chains. It also can promote the change of the direction of force chains and restrain the increase of unbalanced coefficient of bearing capacity of force chains. These findings would expand the powder densification theory by considering about the change of tribological behavior and the evolution of force chains. And they would further expand the theoretical basis of powder compaction in tribology mechanism from the perspective of granular matter mechanics.