The deformation and mixing of several Ni/Al powders under shock wave loading: effects of initial configuration

Abstract

The shock wave initiation of ultra-fast chemical reactions in inorganic powder mixtures requires the reactants to be blended within the shock front or shortly behind it. As such, the details of particle deformation are crucial to understanding the sequence of events leading up to the shock initiation of these systems. It is known that the initial configuration of a powder (i.e. the mixture composition and particle morphology) can have a significant effect on the degree of mixing that is achieved under shock wave loading. However, it is difficult to fully resolve this mixing behaviour in shock compression experiments due to the time and length scales involved. In this work, the shock wave deformation and mixing of six distinct Ni/Al powders are studied at the particle level using finite element simulation. Attention is focused on the Ni/Al interfaces that are formed since overall mixture reactivity depends on the specific amount of reactant interfacial area and on conditions induced at those interfaces. The analysis reveals (i) a rank ordering of the powders based on reactant interfacial area formation, (ii) a scaling relation for the rate of Ni/Al interface production and (iii) the distributed nature of Ni/Al interface temperature and dislocation density over a range of shock stress. Finally, it is shown that particle velocity differentials tend to develop across Ni/Al interfaces when the compacted powders are reshocked by reflection waves. The velocity differentials stem from the heterogeneity of the aggregates and are hypothesized to drive fragmentation processes that enable ultra-fast reactions on a sub-microsecond time scale.

Numerical modelling of shock-induced chemical reactions (SICR) in reactive powder mixtures using smoothed particle hydrodynamics (SPH)

“…Discrete particle numerical algorithms have been developed over the past two decades [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] which achieved particle-level resolution of pressures, temperatures and plastic strains due to shock compression. Among these works, to the best of our knowledge, only Do and Benson [29,32], Reding and Hanagud [42], Reding [43] and Qiao et al [40] dealt with coupling chemical reaction kinetics with the mesoscale shock compaction calculations.…”

Shock Loading of Granular Ni/Al Composites. Part 2: Shock-Induced Chemistry

“…17,18 These processes make experimental characterization and predictive modeling of these composites very challenging due to the extremely short length (10−100 nm) and time (1−10 ns) scales involved. 19,20 Atomistic simulations of shock-induced chemical reactions in reactive granular materials have been handicapped by their computational cost, leading to finite size effects, 21,22 idealized geometries, 6 and short simulation time scales. In this work, large-scale and long-time scale MD simulations are used to follow the chemistry that occurs during and after the propagation of the shock wave through a granular Ni/Al material.…”

“…Shock loading of granular composites results in complex phenomena, such as those described in Part 1 of this paper, including the localization of energy as pores collapse. The latter can occur either via plastic deformation for relatively weak shocks or via material jetting at high shock strengths. , These processes make experimental characterization and predictive modeling of these composites very challenging due to the extremely short length (10–100 nm) and time (1–10 ns) scales involved. , …”