| In recent years,China’s railway operating mileage has been increasing,and the volume of cargo transportation has increased year by year,and with the improvement of bearing capacity,heavy-haul trains have higher and higher requirements for brake pad materials.The use of relatively single metal and the friction material prepared by conventional means are gradually no longer applicable,and the composite materials that use a variety of metals or non-metals to cooperate with each other to make up for their respective defects have become a hot spot in people’s research.However,the preparation of composite materials is more difficult,and the mass fraction of different added phases needs to be strictly controlled according to the proportion,which can be solved by powder metallurgy technology at one time.Spark plasma sintering(SPS)is a more advanced preparation method in the field of powder metallurgy,with rapid heating,purification of the particle surface,inhibition of grain growth and realization of direct connection between metal and ceramics,the process is to apply a controllable pulse current on the pressure-bearing conductive mold,the use of current through the powder and its void part when activating the particle surface,breaking through the residual gas in the void to produce partial discharge and particle self-generation to promote the combination of powder,in addition to the conductive mold can also add an external heat source to the powder.Thanks to the excellent molding effect and production efficiency,the practical application of this technology is becoming more and more extensive,and the research on the molding process of this technology is also more and more in-depth,but because this process is extremely complex and carried out in a closed environment,and equipment cannot be observed and measured,there are still some differences in the understanding of its mechanism.In this paper,the friction material was prepared by SPS sintering technology,and the influence of different sintering parameters on the sintering process was analyzed by selecting copper as the matrix and iron,silica and zirconium dioxide as the additives.JMatpro was used to calculate the thermomechanical constitutive relationship,thermophysical parameters and electromagnetic physical properties of metal particles,and the influence of temperature on the relevant quantities of the simulation was analyzed.According to the proportion of each material in the powder,the stacking model of powder particles is generated in EDEM discrete element software to simulate the accumulation of the powder;The coordinate position information is used to establish a three-dimensional model at mesoscopic scale,and the mechanical compression simulation involving the influence of temperature factors is carried out in ABAQUS finite element software to simulate the shrinkage behavior of the powder during sintering.According to the compressed particle deformation results,the electrothermal coupling simulation was carried out in the COMSOL Multiphysices finite element software to simulate the distribution of current,temperature,etc.in the powder,which considered the influence of temperature on the physical parameters of the material and the change of the mechanical results on the contact conduction.Therefore,the force-heat-electricity three-field coupling simulation of discrete particles in the sintering process is realized,and the applicability of the model is verified by experimental comparison,and the changes of particles during sintering and the distribution of current and temperature at the mesoscopic scale are analyzed.Finally,the calculation of two-phase fluid and heat convection was carried out by introducing the air phase,and the generation and flow change process of the melt after metal melting were simulated. |
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