Simple Design Method for Ceramic Tube Pressure Housings

Abstract

Even for ultra deep sea applications, pressure housings using ceramics can obtain positive buoyancy because ceramics typically have an outstanding compressive strength-to-weight ratio and elastic modulus. Nevertheless, ceramic housings have not been used widely to date because their characteristics as brittle materials complicate design efforts. This article presents a design method for a ceramic tube pressure housing applicable to ultra deep sea usage, particularly addressing the material properties of the metal end caps which contact the bearing surface of the ceramic tube. The housing consists of aluminum alloy end caps and a ceramic tube with wall thickness determined using a critical buckling equation for infinite cylinder length. The cap design uses only the conventional method for metal housing without a special design for reducing tensile stress on the ceramic cylinder. An investigation based on plastic contact mechanics indicates that aluminum alloy caps that have lower yield strength and an elastic and tangent modulus than those of other metals reduce tensile stress at the ceramic tube end via reduction of the contact pressure. Furthermore, nonlinear finite element analysis results indicate only slight tensile stress on the end surfaces of the ceramic tube and provide markedly low tensile failure probability. Comparison to simulated results with the titanium alloy cap model highlights the aluminum alloy cap's effectiveness at reducing tensile stress on the ceramic tube end. The reliability of this simple and easily introduced design method for ceramic tube housings is demonstrated through pressure testing and observations.