Effects of initial density and pulse width on damage evolution and ignition response of PBX under multi-pulse loading

Ignition of polymer bonded explosives (PBXs) may occur under impact loading, while the ignition mechanism remains unclear because of the non-uniformity of PBXs and the complexity of loading conditions. In this study, the dynamic mechanical behavior and ignition response of PBXs with different initial densities under different pulse width conditions were systematically investigated using an improved split Hopkinson pressure bar device. The macroscopic deformation, mechanical response, damage evolution, ignition delay time and ignition threshold were quantitatively characterized. Under multi-pulse loading, the specimens sequentially underwent axial compression, radial expansion, crack initiation and propagation, local failure and ignition reaction. Impact ignition mainly occurred during the stage of rapid damage accumulation, where hotspots were generated by localized heat accumulation dominated by shear friction. A specific incident energy ignition criterion was proposed to replace the traditional strain rate criterion, and it provided an accurate description of the experimental results. The minimum measured specific incident energy required for ignition increased with increasing pulse width, whereas the critical ignition delay time decreased as the pulse width increased. The effects of initial density, loading strength and pulse width on the damage mechanism and ignition response of PBXs were clarified.