Use of Functionally Graded Material Layers in a Two-Layered Pressure Vessel

This work explores the possibilities of using functionally graded material (FGM) layers to reduce normal and shear stress gradients due to internal pressure and thermal loadings at the interface of a two-layered wall pressure vessel. The two walls are made of an internal thin metallic layer (titanium used as a liner to avoid a chemical/physical reaction between the gas and the external layer) and an external thick layer (carbon fiber used as a structural restraint). Two main geometrical elements are investigated: a cylindrical shell and a spherical panel. The shell analysis has been made by referring to mixed layerwise theories, which lead to a three-dimensional description of the stress/strain fields in the thickness shell direction; results related to the first order shear deformation theory are given for comparison purposes. It has been concluded that it is convenient to use FGM layers to reduce shear and normal stress gradients at the interfaces. Furthermore, the FGM layers lead to benefits as far as buckling load is concerned; lower values of in-plane shear and longitudinal compressive stresses are, in fact, obtained with respect to a pure two-layered wall.