Propellants Explosives Pyrotechnics, Vol.44, No.7, 850-857, 2019
Thermal Cycling and Ratchet Growth of TATB and PBX 9502
The irreversible volume expansion, or ratchet growth, of TATB and PBX 9502 (95 weight% TATB) compactions has been quantified over a wide range of thermal cycles. While the precise TATB texture distributions of these specimen sets are likely different from each other, we believe they are consistent within each set, as the expansion data show reproducibility and consistency. These data provide a baseline characterization of the ratchet growth phenomenon in these materials. The increased expansion that comes with changes in the temperature range of the cycles is quantified, repeated hot cycles growing far more than cold. For thermal cycles above ambient where the temperature range is increased in subsequent cycles, the growth of a given cycle is shown to be dictated by previously-established growth trajectories, and the specimen will grow according to the growth potential associated with the temperature range of the present cycle. Alternating hot-cold cycles greatly enhances the cold-cycle contributions as compared to the growth of cold cycles alone. These "rules" of ratchet growth are first established, then observed to hold true for more complex sequences of hot and cold cycles. A simple equation is used to parameterize the response of individual data sets.