Numerical Simulation On The Compaction Densification Of Different Initial Packing Structures Of Three-Dimensional Ellipsoidal Particles

The densification behavior of the non-spherical particles from initial packing to the compaction under external energy can be systematically studied by mesh discretization on the traditional finite element models.This method makes all steps in the simulation be correlated and reduces assumptions in the model,which makes the simulation results more realistic and accurate.In this thesis,a multi-particle finite element method(MPFEM)model was utilized to study the packing densification of different initial packing structures of ellipsoidal particles when subjected to single action die compaction,where the ordered initial packing structures including E-BCC,E-FCC,and DE-FCC were constructed by geometrical method using Solidworks software and the disordered or random packing structures were generated by DEM method.Then various model parameters were modified and imported into the commercial finite element software(Marc)to for numerical simulation.The compaction densification process of different initial packing structures of ellipsoidal particles and the properties of corresponding compacts were subsequently discussed and analyzed.The difference of compaction densification behavior between the ellipsoidal and spherical particles lies in the sphericity and orientation of the former being the significant influencing factors.Even for the ellipsoidal particles with the same shape,the difference in initial packing structures can also lead to different compact properties,where disordered packing structure differs from ordered packing structures and discrepancy in each ordered packing structure can be reflected by different packing ways,which can all lead to distinctive contact deformation and densification mechanism when subjected to external pressure.For each initial packing structure,the transmission of external energy is mainly completed through the contacts between particles,where the force transmission is the most representative.The mechanical laws of contact transmission between particles were obtained by the nodal force output in the contact area(Mises stress,the contact normal force)and data processing.At the beginning of the suppression,Mises stress would be increased rapidly with the increase of density increased,then quickly reduced beyond the yield limit,and subsequently increased with the increase of deformation degree,finally slow rising with a small extent.All that verified the mechanical behavior of metal plastic deformation well under Mises yield criterion.On the other hand,the contact normal force as a kind of surface contact force is closely related to the size and number of the contact surface nodes.At the beginning,contact deformation mainly relied on the node size increased and rised with the increase of thrust pressure.Gradually ellipsoid contact deformation depended on number increased of node,the role of nodes in the unit normal contact force would be reduced and when the final deformation attained to be a certain extent,the normal contact force increased with the increase of thrust pressure again.The compaction process and the macro properties of the compacts were discussed through the construction of complicated and accurate micro-particle model,which includes the effects of friction coefficient,aspect ratio,and initial packing density on the compaction densification.And corresponding conclusions were reasonably explained from micro scale.Among them,the lower internal friction coefficient of particles was,the denser and more uniform density distributions of compact were in the progress of pressing.Meanwhile,Both large aspect ratio and low initial bulk density are factors to debase the density of compact in the end.The results can provide valuable references for the study of future high performance powder metallurgy,ceramics,and particulate reinforced composites,which implies important theoretical and practical significance.