Sensitivity of PBX-9502 after ratchet growth

Ratchet growth, or irreversible thermal expansion of the TATB-based plastic-bonded explosive PBX-9502, leads to increased sensitivity, as a result of increased porosity. The observed increase of between 3.1 and 3.5 volume percent should increase sensitivity according to the published Pop-plots for PBX-9502 [1]. Because of the variable size, shape, and location of the increased porosity, the observed sensitivity of the ratchet-grown sample is less than the sensitivity of a sample pressed to the same density. Modeling of the composite, using a quasi-harmonic EOS for unreacted components [2] and a robust porosity model for variations in density [3], allowed comparison of the initiation observed in experiment with behavior modeled as a function of density. An Arrhenius model was used to describe reaction, and the EOS for products was generated using the CHEETAH code [4]. A 1-D Lagrangian hydrocode was used to model in-material gauge records and the measured turnover to detonation, predicting greater sensitivity to density than observed for ratchet-grown material. This observation is consistent with gauge records indicating intermittent growth of the reactive wave, possibly due to inhomogeneities in density, as observed in SEM images of the material [5].