Friction-induced ignition study of HTPB propellant based on a coupled chemo-mechano-thermodynamic model under ultrahigh acceleration overload conditions

A method is proposed to assess the friction-induced thermal safety of free-cast solid rocket motors subjected to ultrahigh acceleration overload conditions. By measuring the ignition possibility of propellant specimens during the extrusion friction process and determining the reaction kinetics and constitutive parameters, a coupling model considering the thermal, mechanical and chemical effects is proposed. The kinetic parameters of the thermal decomposition reaction and the parameters of the constitutive model are then calibrated accordingly by compression tests covering a large range of strain rates and differential scanning calorimetry (DSC) tests. Experiments on friction ignition are then conducted to validate the developed model at different extrusion pressures and sliding velocity conditions. The results show that the model developed in this work can accurately predict the ignition possibility and temperature distribution of the propellant. Based on this model, dynamic process simulations of a solid rocket motor subjected to an ultrahigh overload of 10000g were performed. Friction primarily occurs at the bottom and side surfaces of the propellant grain, and ignition is more likely to occur at the outer apex of the bottom surface. The temperature rise in the early stages of overload is primarily driven by the frictional conversion of the bottom surface.