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

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

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

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

5. Review: DEM Simulations Simulation of impaction with DEM

6. Review: Relative Topics Crater shapes jetProjectile shapes

7. Critical Thickness of granular matter for impact load Physical test device: cylinder projectile glass steel sphere b =30cm m =167g D l =20cm D b =5cm H =0.5cm ρ =2.56g/cm 3 In experiment, drop projectile from h = 50 cm into the granular bed with different granular thickness H. h H Load sensor Projectile acceleration Force on bottom plane

8. test material: regular glass particles and irregular sand particles Filling thickness: H=0 ~ 9cm Particle diameter parameter (mm) D fine glass coarse glass fine sand coarse sand 0.4 4.0 0.4 1.5 0.6 5.0 0.7 2.5 0.5 4.5 0.5 2.0 Four different granular materials Granular Material Buffering of Critical Thickness fine glass coarse glass fine sand coarse sand

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

10. Impact loads under different granular thicknesses P 1 ： Peak1 is from the force between weight and granular bed P 2 ： 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. Typical Impact Force-time Curves Impact force-time curves fine glass 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 with different materials fine glass coarse glass fine sand coarse sand H=0.5cm

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

13. Effect of Thickness and Velocity on Impact Peak Impact load peak under different impact velocities and granular thicknesses 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

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

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

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

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

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

19. Coordination number of projectile Mean 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 chain Coordination Number

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: (1) Energy dissipation in the impact process with DEM simulation. (2) Measurement of impact load on projectile. (3) Engineering applications.

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