Abstract:

HTPB composite base bleed grain (CBBG), which has been widely applied to the base bleed extended-range technology, is a typical particle-filled energetic material and bears both impact and temperature loads in battlefield environments. In order to investigate impact compressive mechanical properties of HTBP CBBG, split Hopkinson pressure bar experiments were conducted at various temperatures and strain rates, ranging from 233 to 323 K and from 1100 to 7900 s$^{-1}$. True stress-true strain curves shows that HTPB CBBG yields and then deforms plastically with strain hardening effect and maintains high toughness under each experimental condition. The stress value at a certain strain increases with the increase of strain rate and the decrease of temperature, but temperature has a more significant influence on impact compressive mechanical behaviors of HTPB CBBG than strain rate. On the one hand, the time-temperature superposition principle was introduced into the cooperative model by taking the correlations between horizontal/vertical shift factor and temperature as WLF function-type equations based on the fact that the temperature range discussed here was higher than the glassy transition temperature of HTPB CBBG. One the other hand, the enhancement effect of strain rate of internal stress was also taken into consideration, and then a new stress model was proposed. The smooth horizontal shift factor-temperature curve, vertical shift factor-temperature curve and master curve of yield stress were built at a reference temperature according to experimental results to obtain the parameters in the proposed model. The comparison between the model prediction and experimental data indicates that the developed model can precisely describe the bilinear dependence of yield stress on strain rate at temperatures of 233$\sim $323 K. The proposed model points out that the strain rate effect is derived from internal stress at low strain rates while it is derived from drive stress at high strain rates.

Key words: HTPB composite base bleed grain, impact, compressive mechanical properties, the time-temperature superposition principle, yield stress