Ensuring the structural integrity of solid propellant grains throughout storage, transportation, and service remains a major challenge in rocket propulsion systems. Damage initiation strength is one of the most important mechanical parameters for evaluating the safety of solid propellants, yet its determination traditionally relies on extensive mechanical testing under multiple temperature and loading conditions.
To that end, a recent study published in Energetic Materials Frontiers presents a thermo-viscoelastic modeling approach that accurately predicts damage initiation strength over a wide range of temperatures and strain rates while significantly reducing experimental cost.
"Damage initiation strength is one of the key mechanical parameters for assessing the safety of solid propellant grains," explains first author Hui Li. "By combining thermo-viscoelastic constitutive theory with the force–heat equivalence energy density principle, the proposed model enables accurate prediction of damage initiation strength under various temperatures and strain rates using only stress relaxation tests."
Thermo-Viscoelastic Theory Reduces Experimental Complexity
The researchers first established a theoretical elastic modulus based on thermo-viscoelastic constitutive theory and the time–temperature superposition principle. Unlike the conventional elastic modulus method, which requires numerous tensile experiments under different loading conditions, the proposed approach determines the theoretical modulus directly from a series of stress relaxation tests.
“ The theoretical modulus was then incorporated into a damage initiation strength model through the force–heat equivalence energy density principle, allowing the evolution of damage to be quantitatively linked with temperature-dependent viscoelastic behavior ,” says Li. “ This methodology substantially simplifies experimental procedures while maintaining high predictive accuracy. ”
Accurate Prediction Across Temperatures and Strain Rates
The model was validated using composite solid propellants under multiple temperatures and strain rates. “ The predicted damage initiation strengths showed excellent agreement with experimental measurements over the entire testing range ,” shares Li.
The results demonstrated that both temperature and strain rate strongly influence damage initiation. As temperature increased, the damage initiation strength decreased due to material softening, whereas higher strain rates enhanced resistance to damage because of the viscoelastic response of the propellant binder. “ The proposed model successfully captures these coupled effects and accurately reproduces the experimentally observed trends ,” adds Li.
Compared with traditional empirical fitting approaches, the thermo-viscoelastic framework provides a physically based description of damage evolution, enabling reliable prediction under conditions beyond those directly measured experimentally.
Toward Reliable Structural Integrity Assessment of Solid Propellants
The study established a practical methodology for evaluating the mechanical safety of composite solid propellants using a combination of constitutive modeling and stress relaxation experiments.
“ By replacing extensive mechanical testing with a theoretically grounded prediction framework, the proposed method offers a more convenient and cost-effective approach for determining damage initiation strength ,” says senior and co-corresponding author Zhi-Geng Fan. “ The model provides valuable support for structural integrity assessment, service-life evaluation, and reliability analysis of solid rocket motors operating under complex thermo-mechanical environments .”
The findings contribute to the development of predictive mechanical assessment technologies for energetic materials and provide a scalable framework for improving the safety and reliability of next-generation solid propulsion systems.
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Contact author details:
Institute of Systems Engineering, China Academy of Engineering Physics, Mianyang 621900, China. E-mail addresses: lihui200@njust.edu.cn (H. Li) fanzg@caep.cn(Z.-g. Fan)
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Energetic Materials Frontiers
Thermo-viscoelastic modeling of damage initiation strength in solid propellant.
The authors declare no competing financial interest.