Investigations of the mechanical response of dummy HTPB propellant grain under ultrahigh acceleration overload conditions using onboard flight-test measurements

In this paper, to study the mechanical responses of a solid propellant subjected to ultrahigh acceleration overload during the gun-launch process, specifically designed projectile flight tests with an onboard measurement system were performed. Two projectiles containing dummy HTPB propellant grains were successfully recovered after the flight tests with an ultrahigh acceleration overload value of 8100 g. The onboard-measured time-resolved axial displacement, contact stress and overload values were successfully obtained and analysed. Uniaxial compression tests of the dummy HTPB propellant used in the gun-launched tests were carried out at low and intermediate strain rates to characterize the propellant's dynamic properties. A linear viscoelastic constitutive model was employed and applied in finite-element simulations of the projectile-launching process. During the launch process, the dummy propellant grain exhibited large deformation due to the high acceleration overload, possibly leading to friction between the motor case and propellant grain. The calculated contact stress showed good agreement with the experimental results, though discrepancies in the overall displacement of the dummy propellant grain were observed. The dynamic mechanical response process of the dummy propellant grain was analysed in detail. The results can be used to estimate the structural integrity of the analysed dummy propellant grain during the gun-launch process.