Discrete particle simulation of shock wave propagation in a binary Ni+Al powder mixture

Abstract

Numerical simulations of shock wave propagation through discretely represented powder mixtures were performed to investigate the characteristics of deformation and mixing in the Ni+ Al system. The initial particle arrangements and morphologies were imported from experimentally obtained micrographs of powder mixtures pressed at densities in the range of 45%-80% of the theoretical maximum density ͑TMD͒. Simulations were performed using these imported micrographs for each density compact subjected to driver velocities ͑U p ͒ of 0.5, 0.75, and 1 km/ s, and the resulting shock velocity ͑U s ͒ was used to construct the U s -U p equation of state. The simulated equation of state for the 60% TMD mixture was validated by matching results obtained from previous gas-gun experiments. The details of shock wave propagation through the Ni+ Al powder mixtures were explored on several scales. It is shown that the shock compression of mixtures of powders of dissimilar densities and strength is associated with heterogeneous deformation processes leading to focused flow, particulation, and vortex formation, resulting in local fluctuations in pressure and temperature, which collectively are responsible for highly irregular "shock" fronts and unstable high-pressure states in granular media.

The influence of particle morphology on the dynamic densification of metal powders

“…These processes also influence the rise-time of the initial densification front, measured to be 20, 130, and 400 ns for the copper, equiaxed steel, and steel fiber powders, respectively. This increase is linked to the particle/void size, in agreement with earlier experiments on PTFE and mesoscale simulations of wave front character by Eakins [7,8]. Similar mesoscale simulations are planned for the current powder systems.…”

Shock compression of reactive powder mixtures

“…As mentioned previously, mixing and reaction in the micrometre-scale, spherical Ni+Al mixture is suppressed due to the limited deformation of the harder, denser nickel phase. 126,127 This preferentialism is caused by the large differences in properties between the two components, such as density, sound speed, and yield strength. The results of experiments performed on the flake-Ni and equiaxed-Al mixture indicates that there is also an effect of particle morphology.…”

Mesoscale simulation of the configuration-dependent shock-compression response of Ni+Al powder mixtures

“…Real microstructures were constructed from SEM montages of the starting mixtures pre-pressed at various densitites [1]. The travel of the high-pressure disturbance was used to determine the equation-of-state of the mixture material, and compared to the results of real-time experiments for validation.…”