PSI - Issue 14

Author name / Structural Integrity Procedia 00 (2018) 000 – 000

2

Sukamal Adhikary et al. / Procedia Structural Integrity 14 (2019) 127–133

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1. Introduction Infra -Red (IR) heat seeking guided missiles are a potent threat to military aircrafts all over the world. Innumerable aircrafts & helicopters have fallen prey to IR missiles-both Surface to Air Missiles (SAMs) as well as Air to Air Missiles (AAMs). Infra-Red decoy flares have proved to be an effective counter measure to thwart the heat seeking missiles. The decoy flares are prepared from pyrotechnic compositions. The speciality of pyrotechnic mixtures over other explosives like propellants, is exemplified from the fact that the former has both fuel and oxidiser in its inherent composition and is independent of atmospheric oxygen for its functioning. However, owing to their high sensitivity, care in handling, processing, transportation and storage needs to be ensured professionally at all times. Among the different pyrotechnic compositions experimented all over the world, a composition of magnesium as fuel, polytetrafluoroethylene (PTFE) or Teflon as oxidiser and Viton as binder has become widely acceptable and popular as propounded by Kubota (1987) and Koch et al (1999, 2000,2002,2002). Though MTV flares are available in global market, their manufacturing techniques and performance parameters have been intentionally screened from open domain for economic as well as strategic reasons. Hence, there are very limited research papers in open literature and it necessitates further studies on development of these flares. The consistency of performance of the flares when deployed in flight, primarily depends on the structural integrity of the pellets to withstand the aerodynamic forces and also to manifest uniform burning characteristics for specified duration. Hence, the pelleting process is extremely important for successful performance of the decoy flares. To fulfill this objective, the present paper is intended to investigate the density of the mechanically pressed IR decoy flare pellets by varying the process parameters. 2. Experimental details Pyrotechnic MTV composition constitutes of magnesium (purity>97 percent), Teflon or PTFE, Viton (minimum 66 percent of fluorine content) and laboratory grade acetone (≥99 percent purity). The co mposition of pyrotechnic mixture is as given in Table 1. Table 1. MTV Composition Chemical Percentage Magnesium 45-50 2.1 Raw materials utilised for preparation of pyrotechnic composition

PTFE Viton

45-50 2-8

Viton is soaked in acetone overnight. The colloidal solution is mixed with magnesium powder in a twin blade planetary mixer. The slurry formed is dried for approx. 30 minutes in air. Then Teflon powder is added to the wet mass and again mixed in the planetary mixer for uniform mixing. The final mixture is sieved for any sticky mass and kept open overnight to dry overnight and all trace of acetone is removed.

2.2 Process parameters for pelleting

The IR decoy flare pellets are compacted from pyrotechnic mixture. This pelleting is an important process in the development of IR decoy flares since the pellets are deployed in flight from the launchers. Considering the forward velocity of the aircraft and the ambient air flow at varied altitudes of deployment of these flares, it is evident that the pellets are subjected to high aerodynamic loads. Uniform burning characteristics of the pellets have