Buffering Capacity of Granular Matter to Impact Force State Key Laboratory of Structural Analysis for Industrial EquipmentDalian University of TechnologyDalian 116024 ChinaShunying Ji, Xiaodong Chen , Pengfei LiConference on Complex Dynamics in Granular Systems 2013-06-02 ~ 2013-06-08 KITPC, Beijing

Influence of particle shape and size on buffering capacityCritical thickness of granular matter for impact loadConclusionsBuffering capacity of granular matter with DEM simulationIntroductionContent

IntroductionGranular matter: loose arrangement and easy re-packing

Energy dissipationinelastic collision and contact friction

Splash: kinetic energy of projectile converts to kinetic energy of particles

Force chainbreaking and restructuring extend the local impact in spatial domain expand the instantaneous impact in temporal dimension

Energy dissipation system of granular matter to impact loadGranular matter can be used as an effective buffering material to reduce the impact load.

Review: Physical TestsGranular overflow with impactingThe boundary effect of containerImpact test in to granular matter Boundary effect for the impact depth

Splashing and impact energy dissipation of different grain materials

Relationship of crater shape to projectile size, impact height and impact anglet = -7ms t = 5ms t = 33ms

Review: DEM SimulationsSimulation of impaction with DEM

Review: Relative Topics Crater shapesjetProjectile shapes

Critical Thickness of granular matter for impact load Physical test device: cylinder projectile glass steel sphere b =30cm m =167g Dl=20cm Db=5cm H =0.5cm =2.56g/cm3

In experiment, drop projectile from h = 50 cm into the granular bed with different granular thickness H.

test material: regular glass particles and irregular sand particlesFilling thickness: H=0 ~ 9cmParticle diameter parameter (mm)Four different granular materials Granular Material Buffering of Critical Thicknessfine glass coarse glass fine sand coarse sand

Typical Impact Force-time Curve granular thickness H =1cm granular thickness H =6cm Impact force-time curves on the cylinder bottom

Impact loads under different granular thicknesses P1Peak1 is from the force between weight and granular bedP2Peak2 is from the force between weight and bottomtincreases with the thickness increasingThe rule of P1 and P2 with the thickness of granular increase Hc the exchange point

Typical Impact Force-time CurvesImpact force-time curvesfine glassfine sandThe impact load peaks, for both of fine glass and fine sand, decrease obviously with increasing granular thickness.

The buffer capacity of sand is better than that of glass particles.Impact force-time curves with different materialsH=0.5cm

The Critical Thickness Relationship between force peaks with granular thicknesses glass: Hc=5cm sand: Hc=2cm

HHc: impact peaks are not sensitive to the granular thicknessfine glasscoarse glass fine glass coarse glass fine sand coarse sand fine sand coarse sand

Effect of Thickness and Velocity on Impact PeakImpact load peak under different impactvelocities and granular thicknessesHHc: impact peaks change little and the effects both of velocity and thickness recede

Influence of particle size and shape Impact force on bottom Regular particleIrregular particleImpact load on projectile

model: nonlinear contact model force: elastic and viscous force Mohr-Coulomb criterion

normal:

tangental:DEM modelProjectile: m =167g Db=5cmCylinder; b =30cm Dl=20cm H =0.5cmBuffering Capacity with DEM Simulation

Impact force-time curves of the plans bottomthin bedthick bedRelationship between impact load and granular thickness Analysis of Force of Plans Bottom

Thin bed: more peaks appear and present a gradual attenuation, projectile bounces several times , velocity direction changes many times

Thick bed: one peak appears and decays sharply, no bouncing occurs and decreases quickly to balance, velocity direction does not change Displacement curvesAnalysis of Dynamic Dissipation of ProjectileVelocity curvesForce-time curves

initial arrange break and restructure static Force Chain Structures t =0st =0.07st =0.27st =1.20s

Coordination number of projectileMean coordination number of particles

projectile: the coordination number increases with the thickness increasing and reflects the lever of impaction

Particle: each curve of different thicknesses has a break and reflects the change of the force chainCoordination Number

Conclusions1. Critical Thickness: HcHHc: impact peaks change little and the effects both of velocity and thickness recede

2. Influence on impact load of particle size and shape Small and irregular particles have more effective buffer capacity. For large particle material, the influence of particle shape is obvious.

3. DEM SimulationSimilar results obtained as experimental data qualitatively.

Next works: Energy dissipation in the impact process with DEM simulation. Measurement of impact load on projectile. Engineering applications.

Conference on Complex Dynamics in Granular Systems 2013-06-02 ~ 2013-06-08 KITPC, BeijingThanks.