The influence of microstructure and polymorphic conformer on the shock sensitivity of 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX)

ABSTRACT

The influence on 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX) shock sensitivity resulting from damage due to phase transition versus that of the polymorphic conformer and crystal lattice change in heated HMX are explored in this work. Samples of class III HMX at 1.24 g/cm³ are shocked in a modified gap test, which yields quantitative, rather than ‘go/no-go,’ results. Microstructural characterization of similarly prepared samples is used to draw conclusions about the primary driver of the difference in sensitivity between pristine $\beta$-HMX, thermally induced $\delta$-HMX, and HMX that has spontaneously reverted from $\delta \to \beta$-HMX. It is found, surprisingly, that large crystals of HMX incur a slight decrease in shock sensitivity after undergoing $\delta$-phase transition and/or spontaneous reversion from $\delta \to \beta$-HMX. The difference between shock sensitivity results of a significantly smaller HMX particle size distribution are inconclusive using this test configuration. Further testing of the small particle size distribution using a different experimental design that allows lower input pressures may be more useful for comparison. The results of this study indicate that while the increased crack cross-sectional area in HMX crystals drives an increase in impact sensitivity, it drives a decrease in sensitivity in the shock regime for the conditions studied.

KEYWORDS:

• Shock
• sensitivity
• explosives
• δ-HMX
• phase transition

Acknowledgments

The author would like to thank Megan J. Armstrong (Zucrow Labs) for her assistance in sectioning, polishing, and meticulously measuring PMMA disks to be used as attenuators in this work. Additionally, thanks are owed to David A. Lubelski (Birck Nanotechnology Center) for timely electron beam deposition work. Funding for this work, in part, was provided by the Air Force Office of Scientific Research through Award No. FA9550-15-1-0102 under program manager Dr. Martin Schmidt. The authors also acknowledge funding for this work from the ONR contract 000062867 Predictive Chemistry & Physics at Extreme Temperature and Pressure: molecules, crystals and microstructure (PCP@Xtreme). Author N.R.C. wishes to acknowledge support from the Science, Mathematics and Research for Transformation (SMART) Scholarship for Service Program under grant No. 2016-99534.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Air Force Office of Scientific Research [FA9550-15-1-0102]; Office of Naval Research [000062867]; Science Mathematics, and Research for Transformation [2016-99534].