The Effects of TATB Ratchet Growth on PBX 9502

PBX 9502 is a plastic-bonded explosive that contains 95 wt.-% TATB, a graphitic-structured high explosive known to undergo “ratchet growth,” i.e., irreversible volume change that accompanies temperature excursions. Earlier studies have reported changes in TATB-based composites as a function of thermal cycling and density change, however, a clear distinction between density and ratchet-growth effects has not been made. In the work reported here, an “as-pressed density” baseline for the mechanical response of recycled PBX 9502 is established over a density range of interest, then high-density specimens are thermally cycled between −55 and 80 °C to achieve “ratchet-grown” parts in the same low-density region. As-pressed and ratchet-grown specimens with identical densities are then analyzed using microX-ray computed tomography and USANS techniques to obtain information about pore-size distributions. Data show that after ratchet-growth, PBX 9502 specimens contain, in general, more numerous and smaller voids than specimens that were pressed with lower compaction pressures to match the same density. The mechanical response of the ratchet-grown material is consistent with damage, showing lower tensile stress and modulus, lower compressive modulus, and higher tensile and compressive strain, than as-pressed specimens of the same density.