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Development of a liner-less composite CNG cylinder and improved mechanical properties of cylinder materials

Authors Iqbal, Kosar
Issue Date 2008
Summary Composite high pressure vessels are required in many engineering systems such as, gas fuel equipment for space and road vehicles, home gas appliances, rescue devices and therefore improvement of their specifications and production technology continue today. In this study, a new type of CNG composite cylinder without liner has been designed and manufactured. The major issues for manufacturing of a liner-less composite cylinder are selection of the mandrel material; this is because the mandrel should be water soluble or collapsible due to smaller openings at the ends as compared to the cylindrical portion and gas permeability. Aquapour and silica sand materials were selected for mandrel and found that these materials had good sustainability during the high tension and rotation of the winding process. Water solubility of these materials was proved after the successful removal of Aquapour and sand without any damage of the inner surface of the cylinder. Gel-coat and resin rich tissues were used as gas permeable materials. On the basis of the geodesic dome and design laminates sequence, a filament wound composite liner-less cylinder has been successfully manufactured. The mechanical properties and fracture behavior of nanocomposites and carbon fiber composites (CFRPs) containing organoclay in the epoxy matrix have been investigated. Epoxy/clay nanocomposites were fabricated from diglycidyl ether of bisphenol A (DGEBA) epoxy and organoclay. A manufacturing process using the hand lay-up and hot pressing techniques was developed to produce carbon fiber-reinforced laminates with this nanocomposite matrix. The organoclay brought about a significant improvement in flexural modulus, and flexural strength especially in the first few wt% of clay loading. Flexural properties of CFRPs containing organoclay modified epoxy matrix generally followed a trend similar to the epoxy nanocomposite although the variation was much smaller for the CFRPs. It was also observed that the interlaminar shear strength (ILSS) of CFRPs improved by adding 3wt% organoclay. These improved properties of fiber-reinforced polymer nanocomposites are achieved mostly due to the increased interfacial surface areas and improved bond characteristics of the epoxy-clay nanocomposites. The influence of nanoclay on the impact damage resistance of carbon fibre-epoxy (CFRP) composites has been investigated using the low-velocity impact and compression after impact (CAI) tests. The load-energy vs. time relations was analyzed to gain insight into the damage behaviours of the materials. The CFRPs containing organoclay brought about significant improvement in impact damage resistance and damage tolerance in the form of smaller damage area, higher residual strength and higher threshold energy level. The presence of nanoclay in the epoxy matrix induced the transition of failure mechanisms of CFRP laminates during the CAI test, from the brittle buckling mode to more ductile, multi-layer delamination mode. Addition of 3wt% clay was shown to be an optimal content for the highest damage resistance.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008
Language English
Format Thesis
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