Microstructural evolution of particulate explosive materials in drop-weight experiments below reaction regime

The drop-weight impact test is a common method of determining explosive material sensitivity, represented by the height from which a sample is expected to react with 50% probability, calculated from several individual impact tests from which the outcomes are recorded as either "go" or "no go". With this qualitative binary determination as the primary observation of an impact test, the mechanisms determining whether a reaction initiates and propagates are not well understood. A more detailed mechanistic understanding of explosive reactions in drop-weight impact tests have recently been of interest to both the experimental and modeling communities, and recent studies have gained insight with the use of transparent anvils and high-speed imaging for in-situ visualization of material impact and subsequent explosive reaction. In this study, this same setup was used to impact particulate explosive materials from drop heights below their accepted 50% threshold in order to evaluate microstructural evolution resulting from impact when the sample was unreacted. High-speed imaging was used to monitor the state of the explosive immediately before, during, and after impact, and SEM imaging was used to capture the microstructure of the material before and after impact. Microstructural changes will be discussed, as well as phase changes that were shared between these unreacted materials and materials that do experience initiation and propagation resulting from impact.