Abstract
In this paper, 3D particulate scale modelling on the die compaction of DEM generated initial packings of both soft and hard particles was conducted by employing the multiparticle finite element method (MPFEM). The effects of initial packing structures as well as the compaction pressure on the macroscopic and microscopic properties of the whole powder mass and local structures were investigated. In addition, corresponding physical experiments were carried out for model validation. The results show that the compact obtained from the initial dense packing under vibration undergoes yielding stage earlier than that with natural initial packing (without vibration), and the relative density is much higher. Pores that are significantly smaller and with more uniform size and homogenous stress distribution are observed in the former case. Highest stress regions occur in most cases at a grain boundary with large curvature after deformation. Moreover, the high stress in the central part of both soft and hard particles during compaction is significantly reduced after pressure unloading, reaching a new force balance. In this case, the stress is concentrated mainly at the corners of the deformed particles, which creates the risk of cracking during subsequent sintering at either the contact region between particles or the corners. The numerical results are found to be in good agreement with those from physical experiments, confirming the robustness and reliability of the numerical model used in the simulations.
Highlights
Powder metallurgy (PM) has long been an indispensable technology for both advanced and conventional materials [1,2,3,4]
It can be seen that the results of physical experiment and numerical simulation are in agreement, which proves the effectiveness of the model used in our numerical simulation
It should be mentioned that, during the formation of both soft and hard particles, the initial packing structure of powder has little effect on the relative density of final compacts, it can be seen from Figure 2 that it has a significant influence on the early stage of forming process
Summary
Powder metallurgy (PM) has long been an indispensable technology for both advanced and conventional materials [1,2,3,4]. It proved difficult to quantitatively characterize the local density distribution, stress distribution, and particle flow evolution process of the green body in the powder forming process with physical experiments, due to the geometric, material, and contact nonlinearities [7,8,9,10,11]. In this context, various numerical models describing the forming of metal powders have been proposed. From the perspective of metal plastic mechanics, based on the von Mises theory of metal materials, Kuhn [12], Green [13], Shima [14], Gurson [15], Doraivelu [16], and others have
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