International Journal of Scientific Engineering and Technology ISSN : 2277-1581 Volume No.4 Issue No.6, pp: 361-364 01 June 2015 IJSET@2015 Page 361 Permeability Test Measurement of Composite Material for Reusable Launching Vehicles (RLV) Charanjit Singh, Karthik Sunil, Prudhvinath Reddy, Idris Syed Mahaboob, Raja Sekhar Dondapati School of Mechanical Engineering, Lovely Professional University, Punjab-144411 charanjitsingh412@gmail.com, karthiksunil.09@gmail.com, prudhvi143mountaindew@gmail.com, idrismec@gmail.com, rajasekhar9@gmail.com Abstract: Polymer composites are replacing metals over the time due to their light weight, high strength to weight ratio, excellent physical and thermal properties. Hence, they are ideal candidates where weight is of particular concern. One such application is reusable launch vehicles (RLV). Use of polymer Composite materials instead of conventional metal alloys for fuel tank reduces weight of launching vehicle so that more payloads can be carried into space, thereby reducing cost per kilogram of payload. Polymer composites at room temperature show familiar properties but when they are exposed to low temperature, properties change rapidly and show abnormal behavior. Material becomes brittle as temperature is lowered and fails even at low stresses. It becomes further complex when fibrous polymeric composites are used at cryogenic temperatures. In this context, the suitability of polymer composites at low temperature in RLV has to be addressed since during fuelling with liquid hydrogen, the temperature of tanks drops to cryogenic temperature (20K). Polymer matrix composites are well- known class of engineering plastics, capable of withstanding such extreme thermal cycling and low velocity impacts, while retaining their impermeability. Keywords— Composite material, Universal Testing Machine, Cryogenics, Load cell. I. Introduction Composites find numerous structural applications in the aerospace industries due to their low weight, high strength to weight ratio and good thermal and mechanical properties. In recent times composite materials find applications in the design of cryogenic fuel tanks for reusable launching vehicles (RLV) .The structural systems of these vehicles are subjected to severe thermal and mechanical loading since they contain cryogenic liquids like LH2 and LOX. Due to the thermal and mechanical loading, transverse cracks are induced and create a path for cryogens to flow between the laminates of composites. As LH2 is highly combustible, forms a combustible mixture when it comes in contact with Air/O2 and results in hazards for RLV. The permeability of the composite should be kept minimal to avoid such hazards. The cryogenic tanks are investigated as an integrated tank system. An integrated tank system includes the tank wall, cryogenic insulation, Thermal Protection System (TPS) attachment sub-structure, and TPS. In this context it is very important to investigate the effects of permeability on the fuel tank made up of composites. Also, the effects due to mechanical load and pressure need to be investigated. As a whole, the composite must withstand mechanical and thermal loading. II. Literature Survey Ray W. Grenoble and Thomas S. presented the experimental methods and results of the correlation between damage state and hydrogen gas permeability of laminated composite materials under mechanical strains and thermal loads [1]. A specimen made from composite material has been mechanically cycled at room temperature to induce micro crack damage. Leak rate was found to depend on applied mechanical strain, crack density, and test temperature. Hydrogen gas was supplied along the free edges of the specimen. Tensile modulus was found to be decreased, and micro crack damage increased, as the number of cycles increased. Crack density, as a function of ply orientation, was measured and found to correlate with the leak of hydrogen gas through the specimen. Tension modulus and strength were measured at room temperature, –196°C and – 269°C on five different specimen ply lay-ups. Specimens were preconditioned with one set of coupons being isothermally aged for 576 hours at –184 0 C, in an unloaded state. Another set of corresponding coupons were mounted in constant strain fixtures such that a constant uniaxial strain was applied to the specimens for 576 hours at –184 0 C. A third set was mechanically cycled in tension at –184 0 C [2, 3]. The measured properties indicated that temperature, aging and loading mode can all have significant influence on performance. Moreover, this influence is a strong function of laminate stacking sequence. For tension loading, longitudinal, transverse stiffness and strength decreased as the test temperature decreased. Conversely, the tensile shear modulus and strength increased as the temperature decreased. Damage such as transverse matrix cracks (TMC) and delaminations are prone to develop in composites well below the load levels that would result in mechanical failure [4]. This microscopic damage leads to a leakage path for the fuel. The leakage is influenced by many factors, including pressure gradients, micro crack density, connectivity of the cracks, residual stresses from manufacture, service-induced stresses from thermal and mechanical loads and composite stacking sequence. It is expected that there is a direct relationship between leakage and damage opening but the connectivity of matrix cracks is also a major factor affecting the leakage. In this article, the leakage rate through the damage network is discussed based on earlier studies for the opening of damage