Eigenvalue detonation: Particle size effects in aluminized explosives

Experiments demonstrate that incorporating aluminum into high explosives like HMX can significantly influence their detonation characteristics. Specifically, aluminum particle sizes of 150, 15, 7, and $0.5\mu m$ in diameter result in variation to detonation velocity, and pressure within the detonation reaction zone. Pressure histories recorded at the explosive-indicator interface show an initial peak corresponding to the detonation shock pressure, followed by a pressure drop and a subsequent rise to a second peak within $1\mu s$ of the shock front. The presence of double pressure peak profiles are dependent on the aluminum particle size. To replicate the experimental results numerically, we employ eigenvalue detonation theory consisting of two reactions: a bulk exothermic step followed by a bulk endothermic step. The explosives are characterized by JWL equations of state, and reaction rates that account for the melting temperature of aluminum. We find that the experimental results can be matched for the four aluminum particle sizes by varying only two equation of state parameters, and three rate parameters. Double peak pressure profiles arise from Rate Limited Weak Detonation (RLWD), where aluminum particles rapidly absorb energy during HMX decomposition, leading to a sign change in thermicity. Additionally we explore the potential for strong detonations in aluminized explosives through flyer impact simulations, informing experiments on inducing and sustaining strong detonation in aluminized explosives.

Novelty and Significance Statement

This is a follow-on paper to “On the structure and dynamics of strong and weak eigenvalue detonation in condensed explosives”, V. R. Schuetz and D. S. Stewart, Combustion and Flame 263, (2024) 113414. This paper specializes our 3-component model to aluminized explosives, and predicts experimental results for mixtures of explosive and aluminum particles with varying particle sizes. The model shows that both weak and strong eigenvalue detonation exist and shows the dramatic differences afforded by confinement in the case of strong detonation, which has not received much (or no) attention in the literature. Hence the work is novel and open new doors to principles that can be used to improve explosives and understand the effects of aluminum particle additives.