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Principles of ageing of double base propellants and its assessment by several methods following propellant properties

 
: Bohn, Manfred A.

:
Volltext urn:nbn:de:0011-n-4973145 (8.9 MByte PDF)
MD5 Fingerprint: 425480771b41eb04b1816470967ed2d1
Erstellt am: 26.6.2018


Fraunhofer-Institut für Chemische Technologie -ICT-, Pfinztal:
Energetic Materials. Synthesis, Processing, Performance : 49th International Annual Conference of ICT, June 26 - 29, 2018, Karlsruhe
Pfinztal: Fraunhofer ICT, 2018
S.96.1-96.49
Fraunhofer-Institut für Chemische Technologie (International Annual Conference) <49, 2018, Karlsruhe>
Englisch
Konferenzbeitrag, Elektronische Publikation
Fraunhofer ICT ()

Abstract
Nitrocellulose (NC) based double base (db) rocket propellants (RP) are further on in use because of adaptable properties in burning rate and the low signature. The slow ageing during storage is often seen as a major disadvantage. However, this is not the case in reality. If properly manufactured with carefully selected ingredients, in-service times up to 20 years at normal thermal loads (10 to 30°C) can be obtained easily. To secure the in-service time handling of db RP motors, one should use the proven ageing indicators: decrease of primary (added at manufacture) stabilizer, decrease of molar mass of NC, heat generation rate determined by heat flow microcalorimetry (HFMC). They are used to determine the state of chemical ageing and to predict remaining in-service-time. Further ageing indicators are tensile strength at break, mass loss and gas generation. DMA (dynamic mechanical analysis) can answer special questions as well as molar mass distribution and its change with ageing. On the base of these methods the adapted concept for the so-called ‘health’ monitoring (HM) of db RP can be established and implemented.
The term ‘health’ is used to name in short the readiness and compliance of the rocket motor for in-service, in-operation and in-mission use. In connection with in-mission HM means also health management. One concept inside HM is SHM, the ‘structural health monitoring’ of the propellant. To assess the chemical ageing of db RP, first the principle decomposition mechanisms are outlined. The concept of different activation energies is explained and rationalised by newer investigation results. The decomposition ways with different activation energies can influence significantly the prediction and assessment of remaining in-service time. After the selection of ageing indicators, the description of the change of measured data with time must be achieved. This paper shows the principles and ways to predict residual in-service time using stabilizer decrease and molar mass decrease, as well as heat generation rate and tensile strength. For this, the kinetic description models are presented and evaluated as well as simplified methods used to predict a limited in-service time interval for future use of the material. Mass loss as stability indicator is also discussed. A property often somewhat neglected is gas generation, and an important assessment exemplification is discussed in connection with different stabilizers. Representative measurements with DMA are presented. On the whole, the complexity of ageing mechanism seems higher with db RP than with typical HTPB-based composite RP.

: http://publica.fraunhofer.de/dokumente/N-497314.html