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.

Finite element analysis was conducted to study the compaction densification mechanism of Fe-40at%Al composite powders. Firstly, the effect of compaction methods on the property of the compact was characterized by finite element simulation and physical experiment. It was shown that the double compaction could obtain denser compacts comparing with that in uniaxial compaction under the same initial conditions. The simulation result was consistent with the experiment result, and they were well fitted with Van Der Zwan-Siskens model. Furthermore, the effect of compaction pressure was analyzed. It was observed that the increase in compaction pressure could improve the relative density and stress of the compact. Finally, the effect mechanism of the die wall friction was analyzed. And a fitting equation of Fe-40at%Al composite powders was proposed on the basis of Van Der Zwan-Siskens model. The results indicated that friction was the primary reason that induced inhomogeneous density and stress distributions.

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.

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.

The problem of dynamic stress concentration in anti-plane motion of a single circular cavity in a serrated boundary strip medium is studied. Firstly, the scattering of SH wave by a circular cavity defect in the straight line boundary strip medium is analysed based on guided wave theory. The scattering of waves around a circular cavity is expressed as series form by the employed wave function expansion method, and compatible scattering guided waves resulting from the reflection of waves off the boundaries of the elastic strip is constructed by repeated image superposition. The coefficients of the wave function expansion are determined based on the stress free condition of circular boundaries with pre-given incident guided waves. Then the center of the cavity is respectively moved to the upper and lower boundaries to form a depression, and the scattering of the SH-wave by the cavity in the strip with the depression is analyzed. The results of finite element method and analytical method are used to verify each other. A number of depressions are set up at the boundary to simulate a serrated boundary. Then the finite element method is used to analyze the SH wave scattering problem in the serrated boundary strip. GRAPHICAL ABSTRACT