Historically, adhesion research related to energetic materials has been focused on examining the interaction between explosive crystals and the substrate of interest. However, this neglects the effects of the binder material in compounds such as Composition C-4 and the various formulations of Semtex. These types of explosives are actually agglomerates comprised of the energetic particulate material and some manner of liquid binder. In the case of Composition C-4, the energetic material is RDX (cyclo-1,3,5-trimethylene-2,4,6-trinitramine) bound by a “liquid” mixture of rubber, plasticizer, and oil. By creating a simulant granular material with the same mechanical properties as ‘live’ compounds, we may understand how the live materials behave during swabbing, improving the ability of swabbing in a security environment to effectively detect these non-ideal plastic explosives. Previous work to this effect has attempted to quantify the effects of applied force, while assuming a constant swipe speed. However, our results indicate that not only is the binder itself non-Newtonian, but the overall agglomerate behaves in a non-Newtonian manner, as well. Hence, the swipe speed could perhaps be one of the principal factors in optimizing contact-based sampling.
Ultimately, this project aims to increase the current understanding of material behavior based on material properties, as well as operator procedure. Our most recent results indicate that our benign surrogate behaves very similarly to live C-4 in compression tests with regard to strain. These tests exhibit a significantly lower magnitude of stress due to the nature of the size distribution included in the overall composite. Our future work will involve tuning our particulate inclusions to establish the benign surrogate as an equivalent material with which contact sampling efficiency tests may be performed, ultimately furthering our current understanding of the mechanical properties of energetic-filled composites. This information will also enable further research to be conducted to evaluate new swab materials, as well as an optimum swipe protocol.
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