Particle Rolling Friction Research Articles

Discrete element method model calibration and validation for the spreading step of the powder bed fusion process to predict the quality of the layer surface

A Discrete Element Method model, including interparticle cohesive forces, was calibrated and validated to develop a tool to predict the powder layer’s quality in the powder bed fusion process. An elastic contact model was used to describe cohesive interparticle interactions. The surface energy of the model particles was estimated by assuming that the pull-off force should provide the strength of the material evaluated at low consolidation with shear test experiments. The particle rolling friction was calibrated considering the bulk density of the layer produced by the spreading tool. The model was validated with the experiments by comparing the wavelet power spectra obtained with the simulations with those of the experimental layers illuminated by grazing light. The calibration proposed in this study demonstrated superior performance compared to our previous methods, which relied on measuring the angle of repose and unconfined yield strength.

Effect of Friction Coupling on Discharge Velocity Profiles and Force Chain Distribution of Maize Particles in Silos

The evolution mechanism of discharge velocity profiles and force chain distribution of maize particles in silos was studied based on the interaction between internal and external rolling friction of particles. Through EDEM, the silo and maize grain models were established for unloading simulation, whose flow pattern was compared with the silo unloading test to verify the rationality of the simulation. By slice observation, we compared and analyzed the time evolution rules of particle mesoscopic parameters under different friction conditions. The results show that the larger the interparticle friction coefficient is, the longer the total discharge time is and the smaller the coefficient of rolling friction between particles, the earlier the particle flow from mass flow to funnel flow. For silos with the funnel, the reduction of interparticle friction will change the limit between the mass flow and the funnel flow, thus increasing the area of the funnel flow. When the coefficient of rolling friction increases, the vertical velocity and angular velocity of the particle near the silo middle increase. However, the effects of internal and external friction coupling on the vertical velocity of the side particle, the horizontal velocity of the whole particle, and the spatial distribution and probability distribution of the force chain are more significant.

Mechanics of load-drag-unload contact cleaning of gecko-inspired fibrillar adhesives.

Contact self-cleaning of gecko-inspired synthetic adhesives with mushroom-shaped tips has been demonstrated recently using load-drag-unload cleaning procedures similar to that of the natural animal. However, the underlying mechanics of contact cleaning has yet to be fully understood. In this work, we present a detailed experiment of contact self-cleaning that shows that rolling is the dominant mechanism of cleaning for spherical microparticle contaminants, during the load-drag-unload procedure. We also study the effect of dragging rate and normal load on the particle rolling friction. A model of spherical particle rolling on an elastomer fibrillar adhesive interface is developed and agrees well with the experimental results. This study takes us closer to determining design parameters for achieving self-cleaning fibrillar adhesives.

Discrete element simulation of the microscopic mechanical structure in sandpile

The formation of three-dimensional sandpile was simulated by using discrete element model. The influence of sliding friction and rolling friction of particles on the formation of sandpile was discussed. The simulation results show that the angle of repose of sandpile is determined by both sliding friction and rolling friction. The trec-shaped microscopic mechanical structure in the sandpile was revealed by the simulation. The stress distribution at the bottom of sandpile was also obtained by the simulation. The simulation results show that when the angle of repose of sandpile is large, normal stress profiles with a clear stress dip near the center of the pile is generally formed, and when the angle of repose of sandpile is small, the maximal normal stress generally appears near the center of the pile. Which type of the stress distribution at the bottom of sandpile will emerge is rather accidental,depending on the real process of pileing.

Fluidization in dry landslides

This paper aims at determining the physical properties affecting the distance travelled by landslides with dry particles, and elucidating the mechanism of the properties affecting landslide fluidization. The procedure is as follows: laboratory landslide experiments were conducted to verify the simulation model which was proposed to represent the movement of landslides. Further, sensitivity analysis for some physical properties affecting the travel distance were conducted using this model. The simulation model could identify the coordinates, velocity and angular velocity for every particle in three-dimensional space, and the kinetic energy of particles consumed by inelastic and frictional collision with each other in the model. The travel distances of landslides simulated by the model were verified by laboratory experiments statistically where the physical properties for the particles and slope angle were changed. Then, sensitivity analysis for the physical properties were conducted using the model to clarify the effect of the properties on the travel distance. It was proven that there were no significant differences between the travel distances represented by the simulation model and those found experimentally using statistical analysis (i.e. the simulation model could represent virtual real landslides). From the sensitivity analysis using the simulation model, the travel distances were positively correlated to volume, or number of particles, and negative correlated to the slope angle, kinetic friction and rolling friction of particles when the initial potential energies were the same. The mass of particles of equal size did not affect the distance travelled. As the number of particles increased, the simulated travel distances tended to be longer compared with theoretical travel distances calculated using the friction between particles and the slope. Consequently, we could determine the distance of the lumped mass model as being critical between fluidized and non-fluidized landslides.