Compaction simulation of crystalline nano-powders under cold compaction process with molecular dynamics analysis A.R. Khoei a, ⁎, A. Rezaei Sameti b , H. Mofatteh a a Center of Excellence in Structures and Earthquake Engineering, Department of Civil Engineering, Sharif University of Technology, P.O. Box. 11365-9313, Tehran, Iran b Department of Civil Engineering, Faculty of Engineering, Bu-Ali Sina University, Hamedan, Iran abstract article info Article history: Received 14 February 2020 Received in revised form 8 June 2020 Accepted 21 June 2020 Available online 02 July 2020 In this paper, the uniaxial cold compaction process of metal nano-powders is numerically analyzed through the Molecular Dynamics (MD) method. The nano-powders consist of nickel and aluminum nano-particles in the pure and mixed forms with distinctive contributions. The numerical simulation is performed using the different num- ber of nano-particles, mixing ratios of Ni and Al nano-particles, compaction velocities, and ambient temperatures in the canonical ensemble until the full-dense condition is achieved. In the MD analysis, the inter-atomic interac- tion between metal nano-particles is modeled by the many-body EAM potential, and the interaction between frictionless rigid die-walls and metal nano-particles is modeled by the pairwise Lennard-Jones inter-atomic po- tential. The mechanical behavior of metal nano-powders under the compaction process is numerically studied by plotting the relative density–pressure, mean stress-strain, and material characteristics–strain curves. Moreover, the nano-powder behavior is visualized by means of the centro-symmetry contour at various stages of the forming process. Finally, the evolution of top-punch velocity on the final stage of compaction process is studied by plotting the compaction pressure against the total energy at various compaction velocities. © 2020 Elsevier B.V. All rights reserved. Keywords: Metal nano-powders Cold compaction Molecular dynamics EAM potential Compaction velocity 1. Introduction Powder metallurgy is proposed as a method of producing the near- to-net shape industrial components from the loose powders under the pressure. In general, the fundamental step in the powder metallurgy technique is the powder compaction process, in which by implementing the pressure, the components with desired characteristics are manufactured. Commonly, the powder compaction process can be cate- gorized into two distinct approaches; the cold die compaction and the hot isostatic pressing. In the cold die compaction, the loose powders are stuck together under the pressure and a dense body with the desired shape, known as the green body, is extracted; although a sintering pro- cess is usually implemented as post-processing to obtain the com- pressed green body. In the hot isostatic pressing, the hydrostatic pressure is exerted simultaneously with the heat on the loose powders that results in an almost homogenous compressed body with the de- sired shape [1]. Some of the notable privileges of the powder metallurgy method are the precision, cost-effectiveness, capability of manufactur- ing complex components, minimizing the machining requisite, applica- ble to a wide variety of metals, alloys, and metal matrix composites. One of the remarkable advantages of this method is the facility in producing the metal matrix composites by mixing various types of powder materials to obtain the required characteristics [2,3]. This capability of powder metallurgy enables to combine various ratios of different metal powders and fabricate the products with variant mechanical fea- tures. Basically, the forming process of powders depends on different types of parameters, such as powder particle specifications, compaction die geometry, compaction velocity, and ambient temperature. Since in the powder metallurgy the components are produced by compacting a set of fine powder particles, the forming process is considerably de- pendent on the structural features, e.g. the hardness, plastic behavior, and surface characteristics, and the geometrical features of powder par- ticles, e.g. the particle size, shape, and distribution. Obviously, due to the vast number of impressive parameters on the powder compaction pro- cess, the experimental investigation of all parameters is not affordable. On the other hand, the numerical simulations can be employed as a fea- sible alternative for parametric investigation of the powder compaction process [4]. In view of the size of powder particles, the numerical simulation of the powder compaction process can be accomplished in three distinct scales; the macro, micro, and nano-scale levels. Traditionally, the dis- crete (micro-scale) and continuum (macro-scale) methods have been used to analyze the powder compaction process [5–14]. In the discrete method, powder materials are assumed as a collection of particles in contact with each other, and simulation is performed by the discrete-el- ement method (DEM). In this approach, the deformation of powder ma- terial is simulated by definition of the inter-particle and particle-die Powder Technology 373 (2020) 741–753 ⁎ Corresponding author. E-mail address: arkhoei@sharif.edu (A.R. Khoei). https://doi.org/10.1016/j.powtec.2020.06.069 0032-5910/© 2020 Elsevier B.V. All rights reserved. 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