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

Abstract

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 -HMX, thermally induced -HMX, and HMX that has spontaneously reverted from -HMX. It is found, surprisingly, that large crystals of HMX incur a slight decrease in shock sensitivity after undergoing -phase transition and/or spontaneous reversion from -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.