Multi-Particle FEM Simulation Of Warm Compaction On Iron/Copper Composite Powders

In recent years,with the rapid development of transportation tools,the construction of high-speed trains is moving towards higher-speed.That means higher requirements are also put on braking devices and braking materials.The tribology material formed by Fe-Cu composite powders through powder metallurgy(PM)is a new type of braking raw material,which has high friction coefficient,stable wear resistance,heat resistance,large load carrying capacity and high performance price ratio.The relative density distribution,internal stress and pore distribution of green compacts are the important factors to the performance of PM material.However,there are few researches on the warm compaction in powder metallurgy at present.Therefore,the two-dimensional(2D)and three-dimensional(3D)multi-particle finite element simulation and modeling on the warm compaction of Fe-Cu powder mixtures are conducted and then followed by physical experiments.The initial packing structure of Fe-Cu composite powder generated by discrete element(DEM)is firstly imported into MSC.Marc software,where mesh division of individual particle,material property definition and other parameters in finite element method(FEM)operations are set to realize the coupling of the two numerical methods.In this work,2D and 3D numerical simulations are respectively conducted identify the advantages and disadvantages of warm compaction compared with those in cold die compaction.The particle deformation,pore evolution,stress transmission and distribution,as well as the microstructure of the powder particles during pressing are systematically analyzed,then corresponding physical experiments on warm compaction of Fe-Cu powders are conducted,and the data are compared with the numerical simulation for model validation.The results indicate that:1.In the 2D numerical simulation,as the upper punch is moving downward,a force chain will be formed between the contact particles.And with the further increase of the pressure,the forces in the force chain transmit from the top to bottom.The cluster formed by contacted Fe particles in the local area during compaction structure will seriously obstruct the densification process,where the particles within or beneath the force chain are shielded by external force network,and such phenomena can be effectively weakened in warm compaction.2.Friction between particles is the main reason of pressure loss during warm compression.As the pressing progresses move on,the elastic and plastic deformation of the particles increased significantly and contact situation between the particles changes from previous point contact to face contact and face contact area continuously increases.As a result,the frictional force increases and the pressure loss value gradually increases as well.3.During warm compaction,the lamination phenomenon can be observed in the compact in early compaction stage,which can be ascribed to the effects of boundary conditions.In this case,the porosity along the compaction direction takes on fluctuation.With the increase of the compaction pressure,this fluctuation is gradually impaired and the porosity distribution in the compact tends to be uniform.4.The pore filling during warm compression on Fe-Cu composite powders is mainly achieved by the large deformation of Cu particles,and the influence of warm compaction on the deformation of Cu particles is relatively high,while that on Fe particles is relatively low.The warm compaction can significantly reduce the pore size between the Cu particles and other contacted particles,which aids a higher relative density of the compact.