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Dynamic Mechanical Properties of Artifcially Aged Double Base Rocket Propellant and the Possibilities for the Prediction of Their Service Lifetime

Matečić-Mušanić S., Sućeska M.

Central European Journal of Energetic Materials

2013

Vol. 10, no. 2

225--244

The ageing of double base (DB) rocket propellants, as a consequence of the chemical reactions and physical processes that take place over time, has a signifcant effect on their relevant properties, such as chemical composition and mechanical and ballistic properties. The changes to relevant properties limit the safe and reliable service life of DB rocket propellants. Accordingly, numerous research efforts have been undertaken to fnd reliable methods to measure the changes caused by ageing in order to assess the quality of DB rocket propellants at a given moment of their lifetime, and to predict their remaining service lifetime. In this work we studied the dynamic mechanical properties of DB rocket propellant artifcially aged at temperatures of 80, 85 and 90 °C, in order to detect and quantify changes in the dynamic mechanical properties caused by ageing, and to investigate the possibilities for the prediction of service lifetime. Dynamic mechanical properties were studied using a dynamic mechanical analyser (DMA). The results obtained have shown that ageing causes signifcant changes in the storage modulus (E´), the loss modulus (E˝) and the tan δ curves’ shape and position. These changes are quantifed by following some characteristic points on the E´-T, E˝-T, and tan δ-T curves (e.g. glass transition temperatures; storage modulus, loss modulus and tan δ at characteristic temperatures, etc.). It has been found that the monitored parameters are temperature and time dependent, and that they can be shown to be functions of the so called ‘reduced time of artifcial ageing’. In addition, it has been found that, on the basis of known changes in viscoelastic properties as a function of time and ageing temperature, and the known kinetic parameters of the ageing process, it is possible to calculate (determine) the change in the properties at any ageing temperature provided that the mechanism of the ageing process does not change. Unfortunately, the use of kinetic parameters obtained by artifcial ageing at high temperatures (above 60 °C) for the prediction of the propellant lifetime will not give reliable results, because the mechanisms of ageing at 85 °C and 25 °C are not the same.

Applicability of Dynamic Mechanical and Thermal Methods in Investigation of Ageing Processes of Double Based Rocket Propellants

Matečić-Mušanić S., Sućeska M., Bakija S.

Central European Journal of Energetic Materials

2007

Vol. 4, nr 1-2

45-65

Ageing of double based rocket (DBR) propellants, as a consequence of chemical decomposition reaction, as well as physical processes (migration of low molecular constituents: plasticizers, etc.) has significant influence on their relevant properties (e.g. decrease of molar mass of nitrocellulose, decrease of stabiliser content, decrease of specimen mass, change of mechanical and thermal properties, etc.). The change of relevant properties of DBR propellants limits their safe and reliable service life. Even more, under certain conditions decomposition of a DBR propellant may become autocatalytic, which can lead to self-ignition of the DBR propellant. Because of that, it is very important to find out reliable methods for determination of propellant stability at a given moment of time, as well as to predict self-ignition probability under given conditions. In this work we studied dynamic mechanical and thermal properties of DBR propellants artificially aged for different period of time at 90 C, in order to detect and quantify changes in dynamic mechanical and thermal properties that can be used in the propellants stability assessment. Dynamic mechanical properties were studied by dynamic mechanical analysis (DMA), while thermal properties were studied using differential scanning calorimetry (DSC) and thermogravimetry (TGA). The obtained results showed that the ageing caused significant changes of DMA, DSC and TGA curves' shape. The changes are quantified by some of characteristic points on DMA, DSC and TGA curves. It was found out that the most sensitive parameters/characteristic points to the ageing process at DMA curves are: storage modulus at 25 C, storage modulus at softening region, peak width and height on loss modulus curve, glass transition temperature, loss modulus at viscoelastic region, tanδ maximum at viscoelastic region, while the most sensitive parameters at DSC and TGA curves are: peak height and width, heat of reaction, max. heat flow rate, mass loss at a given time, and rate of mass loss at a given time.