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The influence of thermal damage and phase transition on impact and shock sensitivity in HMX systems
thesisposted on 06.01.2021, 15:25 by Nicholas Cummock
Information on the sensitivity of explosives is highly valuable, and the short time scales in which chemical reactions occur in explosives, along with the ability of microstructure to have significant effects on sensitivity, often make this information difficult and expensive to acquire and interpret. Significant changes in impact and shock sensitivity are expected as a result of inducing structural damage in an explosive sample, and thermally damaged HMX-based samples can incur a solid-solid phase transition from beta to delta with non-extreme thermal inputs. Changes in sensitivity due to this phase transition, as well as the simultaneously induced damage, and their relative influence on sensitivity, are of interest to determine experimentally.
Drop-weight impact tests are a commonly used measure of explosive impact sensitivity. Often, simply the L50 of a given material is reported and compared with that of other materials to give a sense of its impact sensitivity. The practice of reporting the impact sensitivity as a single number, the L50, is likely inadequate. It is important to additionally report a measure of the spread of the distribution of reaction probabilities in order to assess the hazard of reaction in situations that may induce a stimulus level well below the L50 of a material. Additionally, multiple distribution forms have been suggested previously for fitting of binary sensitivity data; these distributions typically deviate from each other most near the tails (low and high stimulus levels). The consequences of choosing one distribution form over another in the analysis of explosive drop-weight impact results is explored.
Changes in impact sensitivity due to phase change have received some previous exploration, though the phase change influence is generally conflated with the induced damage upon said phase transition; however, sensitivity changes in the shock regime due to beta to delta-phase change have received little attention. Work is shown which includes methods to isolate variables of HMX phase transition and damage typically incurred upon said phase transition.