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Confining pressure has a significant effect on the mechanical properties of solid propellant, and it is crucial to develop a refined structural integrity analysis and assessment method considering confining pressure effect and nonlinearity of propellant material for the design of propellant grain of a solid rocket motor (SRM), especially for the design of high charge modulus. In this work, an existing viscoelastic-viscodamage constitutive model considering confining pressure effect was implemented as a user-defined material subroutine and verified using a few experiments under various confining pressures. The mechanical responses and safety factor of a typical variable cross-section propellant charge SRM with various charge modulus under ignition pressurization load and room temperature were analyzed and evaluated. The results show that the user-defined material subroutine can well describe nonlinear mechanical responses of solid propellant under different experimental conditions. The Von Mises stress and minimum safety factor considering the confining pressure effect are higher than the value without considering the confining pressure effect, while the Von Mises strain is opposite. In addition, regardless of whether the confining pressure effect is considered or not, the maximum Von Mises stress and strain show a nonlinear increasing relationship with the charge modulus, and the minimum safety factor decreases with charge modulus. However, when analyzing the structural integrity of high charge modulus, using two evaluation methods will yield completely different evaluation results. It is believed that this research can support structural integrity analysis and design of high charge modulus SRM. • The viscoelastic-viscodamage constitutive model was implemented as a user-defined material subroutine. • The mechanical responses of complex stress states loaded HTPB propellant were obtained under confining pressures. • The user-defined material subroutine was verified by a series of verification experiments. • Confining pressure has a significant effect on the structural integrity of a SRM. [ABSTRACT FROM AUTHOR]

To fully characterize the compressive behavior of ethylene propylene diene monomer (EPDM), quasi-static and dynamic compression experiments were conducted for EPDM with a universal testing machine and split Hopkinson bar (SHPB), respectively. Dynamic experimental data employing the two-wave method were used to obtain the stress–strain curves, and the dynamic results were validated. The polymer was compressed under different strain rates varying from 10 −4 to 10 3 . The results indicate that the mechanical properties of EPDM insulation are obviously dependent on the strain rate. An improved Zhu–Wang–Tang (ZWT) nonlinear visco-hyperelastic constitutive model, in which the standard elastic component was replaced by the Mooney–Rivlin hyperelastic model, was developed to predict the mechanical behaviors of EPDM under quasi-static and dynamic impact loading. The model parameters were determined by fitting the model to the experimentally obtained curves by means of the least squares method. The stress–strain curves obtained from the improved ZWT model show good agreement with the experimental curves. This research will further improve the design of the internal insulation structure in solid rocket motors. [ABSTRACT FROM AUTHOR]

• It was found that the deformation-failure behavior of EPDM was dependent on the applied strain rates. • Fracture strains of EPDM increased with the increasing strain rate under quasi-static loading, and this phenomenon is different from previously reported results. • An improved hyper-viscoelastic constitutive model with an energy limiter (in which the constant energy limiter was replaced by a rate-dependent energy limiter) was proposed to predict the rate-dependent deformation-failure behavior of EPDM under quasi-static loading. In order to characterize the rate-dependent deformation-failure behavior of pulse separation device (PSD) of ethylene propylene diene monomer (EPDM), uniaxial constant rate tension, variable rate tension, and stress relaxation experiments were conducted for EPDM in a universal testing machine. It was found that the deformation-failure behavior of EPDM was dependent on the applied strain rates. An improved hyper-viscoelastic constitutive model with an energy limiter (in which the constant energy limiter was replaced by a rate-dependent energy limiter) was proposed to predict the rate-dependent deformation-failure behavior of EPDM under quasi-static loading. The proposed model was first calibrated by fitting it (based on the least squares method) to the data obtained from uniaxial constant rate tension experiments and then further examined by the data obtained from variable rate tension and stress relaxation experiments. The comparative results revealed that the constitutive model with a rate-dependent energy limiter predicted the rate-dependent deformation-failure behavior of EPDM under finite deformation and quasi-static loadings very well. [ABSTRACT FROM AUTHOR]

Highlights • A comprehensive study of hysteretic heating was carried out in HTPB propellant subjected to cyclic loading. • Deterioration of HTPB propellants during fatigue were assessed by the variation of dynamic moduli. • HTPB propellant's ability to resist deformation under compression is significantly greater than that under tension. • A visco-hyperelastic model was proposed to describe mechanical and thermal responses of HTPB propellant. Abstract In order to experimentally measure the heat build-up within a polymer matrix composite under cyclic loading, the real-time temperature monitoring of a solid composite propellant (HTPB propellant) subjected to cyclic uniaxial, strain-controlled fatigue tests at various loading conditions was carried out. The results obtained show that surface temperature of HTPB propellant during the fatigue test increased by up to dozens of degrees, which due to its viscoelastic nature. The effect of applied strain levels and frequencies of tested material on the deterioration of HTPB propellants during fatigue process were quantitatively assessed by the variation of dynamic moduli. It has confirmed that the influences of self-heating on tested materials mainly lies in softening polymeric matrix and extended debonding along particle/matrix interface. Additionally, the pattern of increased fatigue lifetime with a reduction in loading frequency and strain level under was also observed. Moreover, based on an uncoupled thermomechanical coupling algorithm, the finite element analysis incorporating a hyper-viscoelastic constitutive model of tested material was proposed to simulate the mechanical and thermal responses of tested material. The results of simulation agree well with experimental ones, which helps to validate the accuracy of proposed model. [ABSTRACT FROM AUTHOR]

• On-ground DRE experiments were performed with fuel-rich metalized solid propellant. • An in-house computational solver CMRPS was developed using two-way coupled CFD-DEM. • Numerical results of temperature, pressure and thrust agree with experimental data. • Particles distribution and combustion efficiency were statistically analyzed. • Ablation characteristics are strongly related with burning particles. Ducted Rocket Engine (DRE) is an important air-breathing propulsion technology. Its characteristic configuration includes air inlets and afterburning chamber for higher combustion efficiency and better working performance. In this paper, experiments were performed using a fuel-rich metalized solid propellant with an on-ground direct-connect facility. Various sensors were adopted inside the dual-inlet DRE for measuring temperature, pressure and thrust at the air-fuel ratio of 15. Meanwhile, Coupled Multiphase Reacting Phenomena Simulator (CMRPS), an in-house computational solver was developed and validated using two-way coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM). The multiphase reacting flow inside DRE was successfully simulated at the same experimental working condition. Numerical results of the temperature, pressure fields and thrusts have good agreements with the measured experimental data. Temperature contours inside DRE indicate strong coupling effects because of the motion and combustion of metal additives. The highest temperature exists symmetrically near the downwind areas of dual inlets because of the induced high oxygen concentration and the enhanced secondary combustion. Mass fraction contours of main reacting components reveal the chemical pathways. Initially, propellant decomposes and then various components are injected into the fluid domain. Ammonium Perchlorate (AP) and magnesium react the fastest near the burning surface, which leads to a steep temperature increase there from 1050 K to over 2200 K. Then C-H components react gradually with the left oxygen in the primary combustor, while aluminum particles need to absorb heat and have difficult ignition characteristics because of oxidation cap. Air is induced into DRE through dual inlets, which contributes to the secondary combustion of C-H components and aluminum particles in the afterburning chamber. Besides influencing the temperature field, metal particles have great effects on the velocity field because of inter-phase drag force. Therefore, the central velocity characteristics on nozzle exit have obvious decrease, while thrust is increased comparing to the primary single-phase result. Average combustion efficiency can be statistically calculated with numerous exhausted metal particles. Moreover, thermal protection is important for the use of fuel-rich metalized solid propellant. Much attention was paid to the ablation characteristics inside DRE, which is closely related with the distribution of burning particles. CMRPS is meaning to the understanding and designing of multiphase combustor for higher combustion efficiency, meanwhile novel materials and thermal protection strategies can be pertinently improved for better working performance. [ABSTRACT FROM AUTHOR]