DEM Dynamic Modelling On The Vibrated Packing Densification Of Cuboid Particles With Different Aspect Ratios

The dynamic packing of cuboid particles with different aspect ratios under threedimensional(3D)mechanical vibration is numerically studied by the multi-sphere model and the discrete element method(DEM).Corresponding physical experiments are carried out to validate the proposed numerical model.The influences of vibration parameters on packing densification are studied.In numerical simulations,the macro and micro properties of initial loose packing and final dense packing are characterized.And corresponding densification mechanisms are discussed.In both physical and numerical experiments,cuboid particles with h/b=0.5 are poured into the cylindrical container with a certain rate to form initial loose packing and then dense final packing is realized by exerting mechanical vibration with different vibration amplitudes A and frequencies f to the container.Meanwhile,the effects of vibration parameters on packing densification are studied.It is found that the packing density would initially increase with the amplitude or frequency to a maximum value and then decrease,and the optimal vibration parameters for cuboid particles are identical in the physical and numerical experiments.After eliminating the wall effect in the physical experiment by extrapolating the packing densities in different sized containers,packing densities of initial loose and final dense packings for cuboids with h/b=0.5 are 0.630 and 0.705,respectively.In the numerical simulation,the wall effect is eliminated by selecting gradually reduced cylindrical areas to calculate the final packing densities,and packing densities of initial loose and final dense packings for cuboids with h/b=0.5 are respectively 0.631 and 0.700.The physical and numerical results are in good agreement,indicating the validation of the model used in our numerical simulation.In the numerical simulation,the packing structures of cuboid particles with different aspect ratios are systematically investigated in terms of packing density(ρ),nematic order parameter(S2)and cubic order parameter(S4),coordinate number(CN),radial distribution function(RDF),contact types and force networks.The results show that each aspect ratio corresponds to a certain set of optimal vibration parameters.With the increase of aspect ratios,the peaks of packing density curve appear at aspect ratios of h/b=0.5,h/b=1.0 and h/b=1.5,corresponding to packing densities of 0.700,0.736 and 7.707.After vibration,the nematic order parameter decreases and the cuboids with too high or too low aspect ratios are easier to form orientational order;the cubic order parameter increases but is not related to the increase of packing density.After vibration,the average coordinate number deceases due to the formation of more face to face contacts and the cuboids with too high or too low aspect ratios can form higher average coordinate number.The variation of RDF peaks indicates that cuboid particles can form several specific structures,and the value of these peaks increases after vibration.After vibration,the increase of face to face contacts and decease of face to vertex contacts are fundamental reasons for packing densification of cuboid particles.The force network indicates the number of strong forces increases and that of weak forces deceases after vibration,which promotes the formation of dense packing.