The densification mechanism of Cu–Al mixed metal powder during a double-action die compaction was investigated by numerical simulation. The finite element method and experiment were performed to compare the effect of the forming method, such as single-action die compaction and double-action die compaction, on the properties of compact. The results showed that the latter could significantly raise the densification rate and were in good agreement with Van Der Zwan–Siskens compaction equation. The effects of the different initial packing structures on the properties of the compact were studied. The results showed that a high-performance compact could be obtained using a dense initial packing structure at a given compaction pressure. Additionally, the effects of the Al content and compaction pressure on the relative density and stress distribution were analyzed. It was observed that, with an increase in the Al content at a given compaction pressure, the relative density of the compact increased, whereas the stress decreased. Furthermore, when the Al content was fixed, the relative density and stress increased with increasing compaction pressure. The relationship between the relative density and the compaction pressure under different friction conditions was characterized and fitted according to the Van Der Zwan–Siskens compaction equation. The influence mechanisms of die wall friction on the compaction behavior were investigated. It was revealed that friction is a key factor that causes the inhomogeneity of the powder flow and stress distribution. Finally, the effects of the dwell time and height–diameter ratio on the densification behavior were analyzed, and it was found that an increase in the dwell time promoted the densification process, whereas an increase of the height–diameter ratio could hinder the process.

Metal powder pressing is an important key process in the field of powder metallurgy, and the densification process and the degree of densification are affected by factors such as powder properties, die parameters, and the pressing process. Since it is difficult to accurately calculate the number of powder particles by traditional methods, a multi-particle model combining the discrete element method (DEM) and the finite element method (FEM) is used in this study to analyze the effects of the powder stacking structure, the metal composition ratio, the pressing force, the holding time, and the friction coefficient of the inner wall of the die on the densification process. In the modeling process, each powder particle is treated as an individual and represented using the von Mises yield function and Cauchy stress. In this paper, the bi-directional compression molding process and micromechanical behavior of monometallic copper powders and copper–aluminum composite powders with the same particle size are simulated using a coupled DEM–FEM method, which remedies the lack of research in this field. First, the micromechanical behaviors of the particles during compression molding are elucidated, including shape evolution, stress distribution, and force-chain dynamics; second, the effects of aluminum content, initial packing density, and die-wall friction on densification are quantified; and then the models are validated based on empirical formulas (e.g., Hecke’s and Huang Peiyun’s equations). By sharing multi-scale simulations with parametric analysis and combining theoretical modeling with practical industrial applications, the densification mechanism of composite metal powders is dissected, which provides a sizable example for process optimization.

Two mesomechanics models were analyzed in an attempt to reveal the relationship between stored energy and back stress. It has been indicated that the portion of elastic stored energy due to residual microstresses (E_SR) is closely related to intergranular back stress (X_inter), and the stored energy of dislocations inside grains (E_SD) can be estimated with the plastic work of intragranular back stress (X_intra). Then, the evolution of back stress during cyclic loading was studied, and the plastic work of back stress (W_pB) was calculated with the low cycle fatigue experimental data of Ti-6Al-4V. The result shows that W_pB is partially released at every reverse loading, sufficient to reproduce the evolution of stored energy correctly under cyclic loading. The study also reveals that partially released energy is related to the decrease of X_inter at the initial state of reversal loading resulting from the reduction of the plastic strain incompatibility between grains.

In this paper, the analysis method which coupled discrete element method (DEM) and finite element method (FEM) is used to simulate the double compaction of random packing of Cu and Al composite powders with multiple particle sizes. Cu and Al composite powders with varying particle size ratios from 1:2 to 1:5 were generated by DEM and then imported to MSC. Marc software (MSC.MARC2015 version) to construct FEM analysis. The effects of metal ratios, compaction pressure and size ratios on the relative density and von Mises stress of the compact were studied. The results show that the average relative density of the compact increases with the Al content, and the stress decreases. The stress in the Cu particle is particularly higher than that in the Al particle, mainly because the contact normal force of the Cu particle is nearly parallel at each contact surface. Therefore, the phenomenon of stress concentration is easier to occur within copper particles. When Al content is 30wt.%, the particle size difference enhances densification efficiency by up to 12.3%, as evidenced by an initial relative density increase from 0.7915 to 0.8047, primarily due to smaller Cu particles effectively filling interparticle voids. When the compaction pressure is fixed, the average relative density of the compact with the particle size ratio 1:5 is higher than the others, and the contact forces inside the particles significantly decrease.

In this paper, a discrete element method (DEM) coupled with a finite element method (FEM) was used to elucidate the impact of packing structures and size ratios on the cold die compaction behavior of pure copper powders. HCP structure, SC structure, and three random packing structures with different particle size ratios (1:2, 1:3, and 1:4) were generated by the DEM, and then simulated by the FEM to analyze the average relative density, von Mises stress, and force chain structures of the compact. The results show that for HCP and SC structures with a regular stacking structure, the average relative densities of the compact were higher than those of random packing structures, which were 0.9823, 0.9693, 0.9456, 0.9502, and 0.9507, respectively. Compared with their initial packing density, it could be improved by up to 21.13%. For the bigger particle in HCP and SC structures, the stress concentration was located between the adjacent layers, while in the small particles, it was located between contacted particles. During the initial compaction phase, smaller particles tend to occupy the voids between larger particles. As the pressure increases, larger particles deform plastically in a notable way to create a stabilizing force chain. This action reduces the axial stress gradient and improves radial symmetry. The transition from a contact-dominated to a body-stress-dominated state is further demonstrated by stress distribution maps and contact force vector analysis, highlighting the interaction between particle rearrangement and plasticity.

For the past several years, the behavior of pure Cu powder particles with a normal distribution of sizes during the bidirectional die pressing process has remained a fundamental challenge in the field of powder metallurgy, particularly the interaction between particle size dispersion and stress localization. This study employed a discrete element method–finite element method coupled method to simulate the pressing process of 200 Cu particles with a normal distribution (average diameter: 0.5 mm; standard deviation σ = 0.05, 0.1, and 0.2 mm). The results indicate that, compared to a monodisperse system, increasing the dispersion of particle size (σ = 0.2 mm) can enhance the densification efficiency by 12.3%. This is primarily due to smaller particles filling the interparticle voids during the initial compression. Most importantly, this study identified a unique stress concentration mechanism specific to Cu particle materials: the normal forces between particles are parallel at the interface, leading to local von Mises stress peaks within the particles. This phenomenon does not occur in aluminum or other softer materials. Furthermore, at a compaction pressure of 200 MPa, higher dispersion reduces the pore area by ∼25% and shifts the dominant role in densification from plastic deformation to particle rearrangement. The excellent fit of the Huang Pei Yun and Heckler empirical laws also rigorously validates the model’s effectiveness. These findings address long-standing research gaps and shortcomings in the stress evolution of composite powders and provide an applicable microstructure property framework for the design and production of high density Cu components in aerospace and automotive energy applications.