Double-base Propellant Mechanics Model And The High Strain Rate Applied Research

With the development of technology in the rocket missile, the safety issue of the solid rocket motor has become increasingly prominent. Some shock overload such as high emissivity overload and drop impact may cause the grain structure to deform and crack, which may lead to catastrophic failure. Therefore, the high-speed impact has recently been the research focus of the solid rocket motor integrity, which required to analyze the mechanical response of rocket motor grain under impact loading, and to establish a constitutive model which could describe those mechanical responses.The uniaxial compressive experiment of double-base propellant (DB) was performed on the universal material test machine and Split Hopkinson Pressure Bar (SHPB) under different temperatures, respectively. The resulting stress-strain curves were obtained at strain rates between10-4s-1and103s-1. It indicated that the dynamic failure strength of DB is dependent on the strain rate. Yield stress and yield strain increase with increasing strain rates in the quasi-static tests and dynamic tests, and both of them have an approximately linear relationship with the logarithm of strain. In order to fully describe the relationship at a wide range of strain rates, a power law constitutive equation was adopted. Besides, the mechanical properties are dependent on temperature. As the temperature increase, the material becomes soft and its mechanical properties degenerate. The DB was found to transmit into the glassy state at-40℃and behave as a brittle material, a ductile to brittle transformation phenomenon was observed as well.The coefficients of Zhu-Wang-Tang (ZWT) constitutive equation were obtained by fitting the experimental data using the least square method. Results show that ZWT constitutive equation is sufficient to characterize the mechanical properties of double-base propellant under varying strain rate. The SHPB simulation was also performed to validate the ZWT model supplied by a user subroutine. Good agreement between the numerical results and the experimental data was observed. This demonstrates that the model could characterize the preyielding behavior of DB. Moreover, a numerical analysis of stress distribution in the propellant grain of122mm rockets extended-range missile under emitting was carried out. This work may facilitate the theoretical and numerical analysis of structural integrity analysis of propellant grain and rocket engine design.