Hygrothermomechanical creep and stress redistribution analysis of thick-walled FGM spheres with temperature and moisture dependent material properties and inelastic radius changes

Abstract

In the present research, effects of the hygrothermal degradation of the material properties on rates of the creep strains and stresses and stress redistributions of thick-walled FGM spheres subjected to internal and external pressures, temperature rises, and diffusions are investigated. In this regard, the non-linear time-dependent governing equations of the sphere are derived based on the theory of elasticity, Prandtl-Reuss flow rule, and Norton's creep law and solved using a special iterative solution scheme. The main novelties of the present research are: (i) analyzing the FGM sphere as it is; without dividing it into isotropic homogeneous sub-spheres, (ii) considering the temperature and moisture dependencies of the elastic modulus of the FGM material, (iii) proposing a more general numerical procedure instead of the traditional successive elastic or Taylor's expansion procedures, and (iv) successively updating of the inner and outer radii of the vessel to consider the resulting inelastic creep deformations. Results reveal that the moisture absorption generally increases the maximum values of both the elastic and creep portions of the stresses, strains, and stress and strain rates. The creep process reduces the circumferential stresses in the interior regions and increases them in the outer regions, but even in presence of moisture absorption, the area beneath the radial distribution curve of the circumferential stress remains unchanged.