Multi-shell composite pressure vessel optimization

Conventional cylindrical composite pressure vessels are designed with continuous fiber hoop wraps to counter the primary stresses developed in the shell. In certain applications it would be advantageous to be able to assemble a composite pressure vessel around internal components; however, this forces a discontinuity in the reinforcing fibers in the hoop direction. Previous efforts have shown that multi-shell pressure vessels can be assembled and that functional performance can be realized. The basic concept was to bond together four half-shells with the seams of the inner and outer pair rotated 90 degrees. Unfortunately, closed form analysis could not account for localized stress concentrations that severely limited the ultimate Internal pressure. Further, linear finite element analysis was unable to accurately predict shell stresses and generated exaggerated deflections, but, was useful in understanding the general mode of deformation. Based on deformed shapes, from linear finite element analysis, a first generation modified multi-shell pressure vessel with tapered inner shells was developed and tested, with improved results. This research investigates the design considerations involved in the development of an optimized bonded, multi-shell composite pressure vessel, the determination of critical design parameters, the modeling of stresses in the composite shell, and hydroburst testing of prototype pressure vessels. A non-linear finite element analysis was developed and tapered shell thicknesses were evaluated in an effort to generate optimal pressure vessel performance and to minimize stress concentrations in the joint regions. Optimized test vessels based on the finite element analysis, utilizing dual thickness tapered shells, were hydroburst tested to pressures beyond 14.5 MPa without composite failure. The correlation between experiment and finite element analysis indicates that the optimized, dual thickness tapered, bonded multi-shell pressure vessel is an efficient design capable of closely matching internal pressures of continuously reinforced pressure vessels, up to the level where shell-to-shell bond failure occurs.