Jin-sheng Xu

Review of the Adhesively Bonded Interface in a Solid Rocket Motor

One of the most challenging requirements in a solid rocket motor (SRM) is the integrity of the charge structure which is a multilayer adhesive joint involving the propellant, liner, and insulation. The propellant/liner/insulation interface is considered to be the weakest part of the whole structure. This interface has some of the usual features of an adhesively bonded interface, as well as its own special characteristics: the co-cured process, ingredient migration between interfaces, and complicated damage mechanisms. We give a technical and critical review of the past 50 years of existing research on many aspects of the propellant/liner/insulation interface in terms of the adhesive properties and adhesive mechanisms, ingredients migration, damage determination, and fracture analysis. To present a comprehensive outline of this interface we also clarify some remaining problems which should be addressed in the future. With significant improvements in the theoretical and experimental studies of the propellant/liner/insulation interface, the problem of integrity failure of the charge structure in SRM will be well resolved.

Numerical study of the internal flow field of a dual pulse solid rocket motor including conjugate heat transfer

Numerical simulations were performed to study the influence of the inside diameter of the pulse separation device port on the flow features and the local heat transfer characteristics in a dual pulse solid rocket motor. A lower–upper symmetric Gauss–Seidel implicit dual time-stepping method was applied to address the problem of unsteady flow. A high-resolution upwind scheme (AUSMPW+) and Menter’s shear stress transport turbulence model were employed to solve the Reynolds-averaged Navier–Stokes equations. The conjugate heat transfer strategy was realized by enforcing a common temperature and heat flux at the fluid–solid interface. After validating the accuracy and reliability of the numerical algorithm by comparison with experimental cases, the internal flow of a dual pulse solid rocket motor was simulated. The results show that the magnitude of the velocity, the wall shear stress, and the turbulent kinetic energy downstream of the pulse separation device port decrease with increasing pulse separation device port diameter. The local heat transfer coefficient increases sharply downstream of the pulse separation device port, reaching a maximum within 1–2 diameters downstream of the pulse separation device port, before relaxing back to the fully developed pipe flow value. The peak value of the local heat transfer coefficient reduces as the pulse separation device port diameter increases. Meanwhile with an increasing pulse separation device port diameter, the position of the peak local heat transfer coefficient moves upstream to the head of the first pulse chamber, and appears upstream of the position of the reattachment point by an average of about 28.6%.

Mechanical properties experimental investigation of HTPB propellant after thermal accelerated aging

To get accurate aging mechanical properties of aged HTPB propellant, the thermal accelerated aging experiment method is utilized and the uniaxial tensile experiments were conducted to obtain the mechanical data of aged HTPB propellants, and the maximum tensile strength, σm, maximum tensile strain, em, and the fracture tensile strain, eb, of HTPB propellant with different aging time and various aging temperatures,were obtained, using universal material testing machine. The experimental results show that the σm of HTPB propellant initially increases, subsequently decreases and finally increases with aging time. The em and eb generally decrease with increasing aging time, what’s more, the decrease rate of both em and eb reduce with the aging time. What’s more, the postcure effect and oxidation reaction occurred inside HTPB matrix, including the chain degradation reaction and oxidation-induced crosslinking, were discussed to explain the mechanical aging rule of HTPB propellant.

Modeling and simulation of the debonding process of composite solid propellants

In order to study the damage evolution law of composite solid propellants, the molecular dynamics particle filled algorithm was used to establish the mesoscopic structure model of HTPB(Hydroxyl-terminated polybutadiene) propellants. The cohesive element method was employed for the adhesion interface between AP(Ammonium perchlorate) particle and HTPB matrix and the bilinear cohesive zone model was used to describe the mechanical response of the interface elements. The inversion analysis method based on Hooke-Jeeves optimization algorithm was employed to identify the parameters of cohesive zone model(CZM) of the particle/binder interface. Then, the optimized parameters were applied to the commercial finite element software ABAQUS to simulate the damage evolution process for AP particle and HTPB matrix, including the initiation, development, gathering and macroscopic crack. Finally, the stress-strain simulation curve was compared with the experiment curves. The result shows that the bilinear cohesive zone model can accurately describe the debonding and fracture process between the AP particles and HTPB matrix under the uniaxial tension loading.

Study on Thermal and Mechanical Properties of EPDM Insulation

As the most common insulation material of solid rocket motors, thermal and mechanical properties of ethylene propylene diene monomer (EPDM) composite are inspected in the study. Referring to the results of thermo gravimetric analysis (TGA), composition and morphology of EPDM composite in different thermal degradation degree are investigated by scanning electron microscope (SEM) to inspect the mechanism of thermal insulation. Mechanical properties of EPDM composite in the state of pyrolysis are investigated by uniaxial tensile tests. At the state of initial pyrolysis, composite belongs to the category of hyperelastic-viscoelastic material. The tendency of tensile strength increased and elongation decreased with increasing of heating temperature. Composite behaves as the linear rule at the state of late pyrolysis, which belongs to the category of bittle. The elasticity modulus of curves are almost the same while the heating temperature ranges from 200°C to 300°C, and then gradually go down. The tensile strength of pyrolytic material reach the highest at the heating temperature of 300°C, and the virgin material has the largest elongation.