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The Development of Lightweight Composite Cylinders for use in Demanding Structural Applications
[Thesis]. Manchester, UK: The University of Manchester; 2012.
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Abstract
Portable gas containers are utilised by a wide range of end users to enable the transport of gases such as air and oxygen. Such vessels are well established in the medical and self-contained breathing apparatus (SCBA) markets. The increasing use of CNG and other alternative fuels in automotive applications is a driving growth of high-pressure gas containers in the automotive market. The research presented here concerns the manufacture of pressure vessels through alternative routes, with a focus on braiding, in order to reduce the costs of manufacture. Several mandrel winding methods through braiding were developed in order to wrap aluminium gas cylinder liners. The geometry of the domes presented several challenges to preforming. In particular, achieving high, uniform reinforcement angles in the hoop lamina was not possible by over-braiding the dome sections of the vessel. The vessels were designed and produced to pass pressurisation tests and cyclic loading tests according to the EN12245 test standard. A proof of concept for the braided composite pressure vessels was carried out through a scheme of design and testing. The testing scheme employed braided hoop and helical winding and resin infusion processes to produce braided vessels with performance that was equal to the filament wound vessels. The process identified that the braided reinforcement gave similar strengths to that of the wound reinforcement despite the presence of crimp. The fatigue performance of the braided vessels was found to exceed the performance of the filament wound vessels. Finite Element (FE) models of mesoscale braided tow geometries were produced in order to examine the modulus and stress concentrations in the undulating tows. Good agreement between the experimental modulus and FE modulus was found for the 80˚ braided unit cell model.