The simulation for damage of metal powder compacts during forming
The main models of describe metal powder compacting are introduced in this paper. Based on a new model derived from Lee's metal powder compacting model and plastic theory for porous material, the scent of damage status of two-level flanged metal powder compacts during forming is simulated and the damage state and cracking process of compacts in different load process are followed up.
Micromechanical behaviour of Si-based particulate assemblies: A comparative study using DEM and atomistic simulations
Abstract In this paper, we investigate the micromechanical behaviour of Si-based particulate systems subjected to tri-axial compression loading. The investigations are based on three-dimensional discrete element modelling (DEM) and simulations. At first, we compare the variation of mean compressive stress for a silicon assembly subjected to tri-axial compression, predicted at two different scales: at the particulate scale, using the DEM simulation (mono-dispersed particulates) and at the atomistic scale using the molecular dynamics (MD) simulation results for silicon mono-crystal reported by Mylvaganam and Zhang (2003) [K. Mylvaganam, L. Zhang, Key Eng. Mater. 233–236 (2003) 615–620]. Both the simulation methods considered the silicon assembly subjected to an identical (tri-axial) loading condition. We observed a good qualitative agreement between the DEM and MD simulation results for the mean compressive stress when the assembly was subjected to small volumetric strain. However, at large volumetric strain, the mean stress of the silicon assembly predicted from MD simulation did not scale-up with the DEM results. This discrepancy could be due to that MD simulation is only valid for particle contacts, which are independent of one another and does not consider the inherent ‘discrete’ nature of particulates and the induced anisotropy prevailing at particulate scale. The micromechanical behaviour of particulate assemblies strongly depends on the inherent discrete nature of the particles, their single-particle properties and the induced anisotropy during mechanical loading. At the second stage, using DEM, we present the evolution of macroscopic compressive stress and several micromechanical features for four cases of the commonly used Si based poly-dispersed particulate assemblies (Si, SiC,Si3N4 and SiO2) under tri-axial compression loading. We also present the evolution of several other phenomena occurring at particulate scale, such as the energy dissipation characteristics due to sliding contacts and the features of fabric structures developed during mechanical loading. The study shows that the single-particle properties of the Si based assemblies considered here significantly affect the micromechanical behaviour of the assemblies and DEM is a powerful tool to get insights on the internal behaviour of discrete particulates under mechanical loading.
Correlation between bulk stresses and interparticle contact forces in fine powders.
We present measurements of the tensile strength as a function of the consolidation stress for a set of fine cohesive powders (xerographic toners) of 12.7 microm particle size and with a range of concentration of submicron fumed silica as flow control additive. This additive is well known for its ability to control interparticle adhesion force. Parallel measurements using an atomic force microscope have been carried out on the adhesion force between two individual grains as a function of a controlled previous load force. The effect of the additive on the tensile strength and adhesion force is analyzed. We have found a good correlation between bulk stresses and adhesion forces between individual particles. This correlation is compatible with the existence of a subnetwork of force chains.