A new type of shear loading fixture and tensile testing machine with a refrigeration system was utilized to conduct Hydroxyl-terminated polybutadiene (HTPB) propellant low strain rate (0.01 ~1.00 s À 1 ) shear loading tests at low temperature (223 K ~298 K). The shear strength and shear modulus of the HTPB propellant under different loading conditions were studied, and the master curves of the shear mechanical properties were constructed. It is found that the shear strength of HTPB propellant increases with increasing of shear strain rate and decreasing of temperature. The change of shear strength with temperature and strain rate conforms to the linear double logarithmic relationship. The initial shear modulus has a good linear double logarithmic relationship with the strain rate but changes nonlinearly with the logarithmic temperature. The shift factor of HTPB propellant shear strength and initial shear modulus changes exponentially with temperature after taking logarithm. The master curve of the initial shear modulus of HTPB propellant shows an "S"-shaped change trend, and a linear equation is used to fit the master curve of shear strength to obtain a better fitting effect.

The strength limits of composite solid propellants are different at different temperatures and loading states.To study the ultimate bearing capacity of Hydroxyl-terminated polybutadiene (HTPB) propellant, the tensile-shear loading fixture and propellant specimens were designed, and the tensile-shear tests of HTPB propellant at different temperatures (223-298 K) and strain rates (0.01-1.00 s À 1 ) were carried out. The variation of ultimate load of HTPB propellant with loading conditions was analysed. Based on the twin shear unified strength theory, the strength criterion of HTPB propellant under low temperature tension-shear load was established, and the variation of mechanical parameters and stress limit surface with temperature and strain rate were analysed. The results show that the twin shear unified strength theory can be well applied to the strength analysis of propellants. The ultimate bearing capacity of HTPB propellant is the smallest near the loading angle of 45°. The shape of strength limit surface is an equilateral semi-infinite hexahedron. With the decrease of temperature and the increase of shear rate, the strength limit surface of HTPB propellant expands outward.

In order to study the influence of loading conditions on propellant mesoscopic failure morphology, scanning electron microscopy was carried out to observe the morphology of the failure section of a hydroxyl-terminated polybutadiene propellant under different temperatures, loading speeds, and loading conditions. Using the finite element method, a mesoscopic model of a composite solid propellant was constructed, and the mechanical parameters of the propellant particle–matrix interface were obtained based on the parameter inversion method. A meso-model of a hydroxyl-terminated polybutadiene propellant under different loading conditions was constructed, and numerical results were compared with experimental results to analyze the meso-damage. With decreasing temperature and increasing loading speed, the level of propellant damage increased, and the particle–matrix interface became more prone to damage under the combined action of tensile and shear loads. In addition, with an increasing loading angle, ammonium perchlorate particles were more prone to dewetting.

No abstract

Due to strategic requirements, tactical missiles need to be transported several times before they are launched. For this reason, this study examined the cumulative damage that occurs in a solid rocket motor grain during road transportation. Constant-stress reciprocating tensile tests of a composite solid propellant were designed and carried out, and the characteristic fatigue curve of the propellant was fitted and analyzed. By processing power spectral density data for equipment transportation tests, a vibration acceleration load spectrum for a solid rocket motor grain in the process of highway transportation was obtained. A three-dimensional finite-element calculation model of a solid rocket motor was established, and the stress response of the motor grain was simulated. After this, cyclic loads were obtained using a rainflow counting method. The cumulative damage to the solid rocket motor grain during highway transportation was calculated according to Miner’s linear cumulative-damage model and evaluated. It was concluded that during transportation, the maximum stress of the solid rocket motor is 0.2 MPa, the maximum strain is 0.03, and the maximum displacement is 19.32 mm, all of which are found in the front stress-release boot. After 4000 km driving on the highway, the damage to the front stress-release boot of the grain is thus the greatest, with a value of 0.0796. The damage to the inner hole of the grain was found to be the smallest, with a value of 0.0438.