Viscoelastic solids, such as composite propellants, exhibit significant time and rate dependencies, and their fracture processes display high levels of nonlinearity. However, the correlation between crack propagation and viscoelastic energy dissipation in these materials remains unclear. Therefore, accurately modeling and understanding of their fracture behavior is crucial for relevant engineering applications. This study proposes a novel viscoelastic phase-field model. In the numerical implementation, the adopted adaptive time-stepping iterative strategy effectively accelerates the coupling iteration efficiency between the phase-field and the displacement field. Moreover, all unknown parameters in the model, including the form of the phase-field degradation function, are identified through fitting against experimental data. Based on an introduced scaling factor, the mechanical response behaviors of solid propellant dogbone specimens under cyclic loading, relaxation, and tension are analyzed, and the predictive capacity of the model is demonstrated by comparing the experimental data with the simulation results. Finally, modeling results for Mode-I and Mode-II crack propagation in single-edge-notched specimens indicate that the reduction of viscous energy dissipation will significantly increase the fracture growth rate, but under the same boundary conditions, the crack path remains unchanged.

As an important energy source of solid rocket motors, the mechanical properties of composite solid propellants have always been the focus of attention in the engineering field. The macroscopic constitutive model and the fine-scale mechanical model in the characterisation of propellant mechanical properties was focused on. The development of the two types of models was systematically sorted out. The differences between the models were clarified. The applicable conditions of various models were pointed out. The difficulties and challenges of macro and fine mechanical models in the characterisation of propellant mechanical properties at the present stage were analysed. The proposal of mechanical models represented by cross-scale mechanical models will help to solve the problem of propellant mechanical property characterisation. The key in the future modelling of propellant mechanical characterization is the experimental research under complex conditions, focusing on the development of high precision and high performance multiscale numerical computation methods, as well as the integration of data-driven technology represented by artificial intelligence technology into model innovation.

In order to analyze the effect of different combinations of stretching rates of four-component HTPB propellant on the accuracy of the parallel rheological framework model, a nonlinear viscoelastic constitutive model of the propellants was developed based on the parallel rheological framework method. A constitutive model was constructed by combining experiments with different tensile rates, the corresponding constitutive model parameters were obtained and compared with experimental results using finite element models and numerical calculations. The constitutive model errors of the calibration for different rate groups were compared and analyzed. The results show that the model can be calibrated more accurately when a combination of high rate and low rate groups is used, without the need for extensive experiments at intermediate rates. And the high rate propellant tensile test rate can be up to 3000 mm/min, no need to increase the rate. This analysis provides justified suggestions for simplifying propellant material tests and improving the efficiency of the experiments. Concurrently, it paves an effective way to rapidly predict the mechanical properties of propellant materials.