MULTISHELL 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 a ble to assemble a composite pressure vessel around internal components ; however, this forces a discontinuity in the reinforcing fibers in th e hoop direction. Previous efforts have shown that multi-shell pressur e vessels can be assembled and that functional performance can be real ized. 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 concentrat ions that severely limited the ultimate Internal pressure. Further, li near finite element analysis was unable to accurately predict shell st resses and generated exaggerated deflections, but, was useful in under standing the general mode of deformation. Based on deformed shapes, fr om linear finite element analysis, a first generation modified multi-s hell pressure vessel with tapered inner shells was developed and teste d, with improved results. This research investigates the design consid erations involved in the development of an optimized bonded, multi-she ll composite pressure vessel, the determination of critical design par ameters, the modeling of stresses in the composite shell, and hydrobur st 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 mini mize stress concentrations in the joint regions. Optimized test vessel s based on the finite element analysis, utilizing dual thickness taper ed shells, were hydroburst tested to pressures beyond 14.5 MPa without composite failure. The correlation between experiment and finite elem ent analysis indicates that the optimized, dual thickness tapered, bon ded multi-shell pressure vessel is an efficient design capable of clos ely matching internal pressures of continuously reinforced pressure ve ssels, up to the level where shell-to-shell bond failure occurs.