Accelerated aging characteristics and service life determination models of composite solid HTPB/AP-based propellant

Date

2023-9-08

Author

Yapıcı, Melahat

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The physical, chemical, and ballistic properties of composite solid propellant formulations change over time as a result of the nature of the propellant formulation and its constituent elements, as well as the effects of internal and external stimuli. The propellant aging mechanism is affected by various factors, each of which has a distinct impact on aging behavior. In order to completely understand the propellant properties, it is crucial to comprehend the notion of aging. Additionally, it is essential that the propellant properties molded in accordance with the motor geometry be reflected in the block-based aging tests. The rate of change and the pattern of these property changes must be identified in order to precisely determine the period of time that the propellant properties will reach the prescribed limit values or the service life. In this study, several properties, including density, moisture content, mechanical and viscoelastic properties, microstructural integrity, glass transition temperature, specific heat capacity, calorific value, burn rate, friction, and impact sensitivity, were monitored at elevated temperatures for a period of six months in order to examine and comprehend the accelerated aging characteristics of hydroxyl-terminated polybutadiene/ammonium perchlorate (HTPB/AP)-based composite solid propellant formulations. In order to assess the service life of the propellant, four alternative service life determination models were used utilizing the mechanical properties where the most apparent change was observed. In light of this, an attempt was made to model the change in propellant properties. The Competitive Chain Scission/Crosslinking model, which is used to simulate fluctuations in mechanical properties due to the competitive nature of the propellant aging mechanism, and the Severity Index-based model, which reflects the propellant temperature history to the aging model, were compared with the Layton and Van't Hoff models, which are frequently used as service life determination models. It has been observed that Severity Index-based and Competitive Chain Scission/Crosslinking models represent propellant mechanical property changes more accurately. In terms of density, moisture, specific heat capacity (Cp), glass transition temperature (Tg), and sensitivity properties with aging no significant and consistent variations were found. It has been noted that the mechanical and viscoelastic characteristics of propellants change dramatically with increasing aging time. Propellant rods that were shaped according to the motor geometry were additionally subjected to an accelerated aging study for six months in addition to the block-based aging study. The density, glass transition temperature, specific heat capacity, hardness, and viscoelastic property change of the propellant rods were monitored for a period of six months. The investigated properties for propellant rods were compared with the propellant results aged on a block basis. As a result, the impact of motor geometry on aging has been identified.

Subject Keywords

Propellant aging, HTPB-AP-based composite solid propellant, Service life determination model, Severity index, Rocket motor geometry

URI

https://hdl.handle.net/11511/105590

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Graduate School of Natural and Applied Sciences, Thesis