Research On Jamming Phenomenon In Powder Material Compaction

Particulate matter will form jamming if the disordered state system form yield stressor the stress relaxed time exceed the experiment time, which is a kind of transition fromthe state of liquid-like to the state of solid-like. In order to study jamming status of themesoscopic powder in the process of compacting and the influence of jamming,jamming phenomenon of the system composed of polydisperse particles in the processof single-action pressing is simulated by discrete element method, and the pressing testof iron-based powders is performed by using four-column press. The variation rules ofthe pressure parameter with the density parameter and pair correlation function of thefirst peak with the volume fraction are analysed, the distribution rules of interparticledimensionless contact force and the direction of movement of particles and theevolution rule of interparticle force chain near jamming state are obtained by statistics,meanwhile the variations of friction coefficient of blank surface and density of blank areworked out.The results show that the variation of pressure parameter with density parameteris largely in line with double logarithmic equation; at the critical state of jamming, thecoordination number appear obvious turning point; the pair correlation function of thefirst peak rapidly increases to a stable value with the increase of volume fraction; thenumber of particles that making axial motion is reduced but that of lateral motion isincreased; dimensionless contact force between particles, kinetic energy and velocityreach a relative stable state; particles mainly bear normal load in single-action pressing;the tangential load is relatively small; the movements of particles determine the state ofjamming and the relative stable distribution of the contact force, then influence thedensity distribution of the densification process; the system in jamming state formed therelatively stable force chain structure; friction coefficient of blank surface shows a trendof obvious decrease with the increase of pressing force; at the same condition ofpressing, the disparate jamming packing structure of particles can form different densityof blank, and the smaller particles will be aid to improve the density of blank.Simulation and experimental results validate the influence of jammingphenomenon to densification of powder material, and provide strong reference value forthe actual industrial production.