engleski

Dynamic Mechanical Properties of Artificially Aged DB Rocket Propellant and Possibilities for Prediction of Service Lifetime

The ageing of double base (DB) rocket propellants, as a consequence of chemical reactions and physical processes that take place over time, has significant effect on their relevant properties, such as chemical composition and mechanical and ballistic properties. The changes of relevant properties limit their safe and reliable service life. Accordingly, numerous research efforts are devoted to finding out reliable methods to measure the changes caused by ageing, to assess the quality at a given moment of time, and to predict remaining lifetime of DB rocket propellants. In this work we studied dynamic mechanical properties of DB rocket propellant artificially aged at 80, 85 and 90°C temperature, in order to detect and quantify changes in dynamic mechanical properties caused by ageing, and to investigate possibilities for prediction of service lifetime. Dynamic mechanical properties were studied using a dynamic mechanical analyser (DMA). The results obtained have shown that the ageing causes significant changes of storage modulus (E´), loss modulus (E˝) and tan delta curves shape and positions. These changes are quantified by following some characteristic points on E´-T, E˝-T, and tan delta-T curves (e.g. glass transition temperatures ; storage modulus, loss modulus and tan delta at characteristic temperatures, etc.). It has been found out that the followed parameters are temperature and time dependent, and that they can be shown on the so called reduced time of artificial ageing. In addition, it has been found out that based on known changes of viscoelastic properties as a function of time and ageing temperature, and known kinetic parameters of the ageing process, it is possible to calculate (determine) change of the properties at any ageing temperature, under the condition that the mechanism of ageing process does not change.

ageing; double base rocket propellants; dynamic mechanical analysis; glass transition temperature; life –time prediction; loss modulus; softening temperature; storage modulus; tan delta

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