Hydroxyl-terminated polybutadiene (HTPB) has long been used as a binder in propellants and explosives. However, cured HTPB polyurethanes have not been characterized in a systematic fashion as a function of plasticizer content. In this study, three isocyanate-cured HTPB variants with different amounts of plasticizer were formulated. The materials were characterized across a range of strain rates from 10-3 to 10 6 s-1. Group interaction modeling (GIM) was used to predict the material behavior based on the underlying structure of the polymer. Increasing the amount of plasticizer was found to reduce the strength of the material across all strain rates. GIM was found to overpredict the modulus but predicted the shock response very well.
The performance of energetic materials subjected to dynamic loading significantly depends on their micro- and meso-scale structural morphology. The geometric versatility offered by additive manufacturing opens new pathways to tailor the performance of these materials. Additively manufactured energetic materials (AMEMs) have a wide range of structural characteristics with a hierarchy of length scales and process-inherent heterogeneities, which are hitherto difficult to precisely control. It is important to understand how these features affect AMEMs’ response under dynamic/shock loading. Therefore, temporally and spatially resolved measurements of both macroscopic behavior and micro- and meso-level processes influencing macroscopic behavior are required. In this paper, we analyze the shock compression response of an AMEM simulant loaded under several impact conditions and orientations. X-ray phase contrast imaging (PCI) is used to track features across the observed shock front and determine the linear shock velocity vs particle velocity equation of state, as well as to quantify the interior deformation fields via digital image correlation (DIC) analyses. Photon Doppler velocimetry is simultaneously used to measure the particle velocities of the specimens, which are consistent with those obtained from x-ray PCI. The DIC analyses provide an assessment of the average strain fields inside the material, showing that the average axial strain depends on the loading intensity and reaches as high as 0.23 for impact velocities up to 1.5 km/s. The overall results demonstrate the utility of x-ray PCI for probing “in-material” equation of state and interior strains associated with dynamic shock compression behavior of the AMEM simulant.
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