Buffering Capacity of Granular Matter to Impact Force

1. Conference on Complex Dynamics in Granular Systems 2013-06-02 ~ 2013-06-08 KITPC, Beijing Buffering Capacity of Granular Matter to Impact Force Shunying Ji, Xiaodong Chen , Pengfei Li State Key Laboratory of Structural Analysis for Industrial Equipment Dalian University of Technology Dalian 116024 China

2. Content Introduction Critical thickness of granular matter for impact load Influence of particle shape and size on buffering capacity Buffering capacity of granular matter with DEM simulation Conclusions

3. Energy dissipation system of granular matter to impact load Introduction Granular matter: loose arrangement and easy re-packing Energy dissipation：inelastic collision and contact friction Splash: kinetic energy of projectile converts to kinetic energy of particles Force chain：breaking and restructuring extend the local impact in spatial domain expand the instantaneous impact in temporal dimension Granular matter can be used as an effective buffering material to reduce the impact load.

4. Review: Physical Tests t = -7ms t = 5ms t = 33ms Impact test in to granular matter The boundary effect of container • 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 angle Granular overflow with impacting

5. Review: DEM Simulations Simulation of impaction with DEM

6. Review: Relative Topics Crater shapes jet Projectile shapes

7. Projectile acceleration Force on bottom plane h Load sensor H 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 ρ=2.56g/cm3 In experiment, drop projectile from h = 50cm intothe granular bed with different granular thickness H.

8. Granular Material Buffering of Critical Thickness test material: regular glass particles and irregular sand particles Filling thickness: H=0 ~ 9cm Particle diameter parameter(mm) fine glass coarse glass fine sand coarse sand Four different granular materials

9. Typical Impact Force-time Curve granular thicknessH =1cm granular thicknessH =6cm Impact force-time curves on the cylinder bottom

10. Impact loads under different granular thicknesses P1：Peak1 is from the force between weight and granular bed P2：Peak2 is from the force between weight and bottom Δt：increases with the thickness increasing The rule of P1 and P2 with the thickness of granular increase Hc：the exchange point

11. fine glass coarse glass fine sand coarse sand Typical Impact Force-time Curves H=0.5cm fine glass Impact force-time curves with different materials fine sand • The 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

12. The Critical Thickness fine glass coarse glass fine sand coarse sand fine glass coarse glass fine sand coarse sand • glass: Hc=5cmsand: Hc=2cm • H<Hc: peaks decrease obviously with the increasinggranular thickness • H>Hc: impact peaks are not sensitive to the granular thickness Relationship between force peaks with granular thicknesses

13. Effect of Thickness and Velocity on Impact Peak H<Hc: impact peaks decrease with increasing the granular thickness and increase with increasing the projectile velocity H>Hc: impact peaks change little and the effects both of velocity and thickness recede Impact load peak under different impact velocities and granular thicknesses

14. Regular particle Irregular particle Influence of particle size and shape Impact force on bottom Impact load on projectile Regular particle Irregular particle

15. Buffering Capacity with DEM Simulation DEM model model: nonlinear contact model force: elastic and viscous force Mohr-Coulomb criterion normal: tangental: Projectile: m =167g Db=5cm Cylinder; b =30cm Dl=20cm H =0.5cm

16. Analysis of Force of Plan’s Bottom thin bed Relationship between impact load and granular thickness thick bed Impact force-time curves of the plan’s bottom

17. Analysis of Dynamic Dissipation of Projectile 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 Force-time curves Displacement curves Velocity curves

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

19. Coordination Number 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 chain Coordination number of projectile Mean coordination number of particles

20. Conclusions • 1. Critical Thickness: Hc • H<Hc: impact peaks decrease with increasing granular thickness • H>Hc: 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 Simulation • Similar 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.

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