Crack Initiation in Perforated Propellants under high strain rate impact conditions

The fracture behaviour of gun propellant grains during impact has been measured on a modified Hopkinson Bar which uses a projectile as the input bar. Evidence for the detection of initial minor crack formation in seven-perforated cylindrical specimens of single base, double base and triple base propellant is presented. Under compressive load (pressurization rates of 100 GPa/s-200 GPa/s), minor crack formation does not immediately result in large scale crack propagation or fragmentation of the specimens. The single base and triple base propellant are equally more resistant to crack initiation than the double base propellant when tested in either the end-on or side-on modes. Implications for munition survivability are discussed in terms of mechanical frictional effects caused during compressive loading of cracked propellant or compressive heating in propellant cracks during the ballistic cycle.