Finite Element Analysis of Composite Over-wrapped Pressure Vessels for Hydrogen Storage

This paper presents 3D finite element analysis performed for a composite cylindrical tank made of 6061-aluminum liner overwrapped with carbon fibers subjected to a burst internal pressure of 1610 bars. As the service pressure expected in these tanks is 700 bars, a factor of safety of 2.3 is kept the same for all designs. The optimal design configuration of such high pressure storage tanks includes an inner liner used as a gas permeation barrier, geometrically optimized domes, inlet/outlet valves with minimum stress concentrations, and directionally tailored exterior reinforcement for high strength and stiffness. Filament winding of pressure vessels made of fiber composite materials is the most efficient manufacturing method for such high pressure hydrogen storage tanks. The complexity of the filament winding process in the dome region is characterized by continually changing the fiber orientation angle and the local thickness of the wall. The research work presented in this paper reveals that the continuously changing angle orientation and local laminate thickness in the dome regions can be modeled by a unique approach that utilizes suitable transformations of the macromechanical composite properties and the local coordinate system. Accurate representation of the exterior reinforcement allows for detailed analysis of the dome structure as well as the nozzle/valve connection. A metallic insert is utilized to connect the dome structure to the valve system. A comparative study between different insert geometries and locations in the dome has been performed. It shows that an insert extending through the dome geometry increases the resulting stress at the cylinder-dome juncture. The most effective design approach entails an insert to the boss region.