Reproducibility and applicability of time-temperature superposition for polymer-bonded explosives tested with torsional dynamic mechanical analysis

Characterizing viscoelastic mechanical properties for polymer bonded explosives (PBX) at high strain rates is typically limited by test frequencies of commercial dynamic mechanical analysis (DMA) instruments. While time temperature superposition (TTS) has proven to show some validity for PBX materials to extrapolate viscoelastic response to higher frequencies, little work has been organized in the energetics community to assess reproducibility of results between test methods and laboratories. This work compares TTS results from torsional DMA between Fraunhofer Institute for Chemical Technology (ICT) in Pfinztal, Germany, and the Air Force Research Laboratory (AFRL) at Eglin Air Force Base, USA. Results show some similarity, with frequency dependent differences observed and quantified. This work analyzed a small data set; therefore, opportunities still exist to build statistical confidence of the difference between methods and laboratories. A gage repeatability and reproducibility study is recommended to further assess the, if any, statistically significant differences that could exist between laboratories and/or test methods. Best practices for TTS experiments are also noted for methods used at AFRL to improve data quality and agreement between results. Lastly, results are shared for a HTPB R-45 HTLO based polymer bonded explosive simulant (PBS) with 60 volume % of solid filler to build more confidence in the community that TTS has some validity for PBX materials to predict high frequency viscoelastic response. Quality checks on the PBS sample indicate TTS validity betweeb -60 °C to 70 °C temperature steps, which allows extrapolation of viscoelastic behavior to nearly 109 Hz at a 20 °C reference temperature.