The problem of stability is studied for a nonlinear elastic porous rod with a solid coating for two common types of combined loading - an axial compression of the rod under external hydrostatic pressure, as well as compression and torsion of the rod. A special feature of this paper is that the behavior of a homogeneous coating is studied in the framework of classical (non-polar) continuum model, while to describe the properties of a highly porous rod the Cosserat continuum model is used. By solving the linearized equilibrium equations numerically, for a number of specific porous materials and coatings, the critical curves and corresponding buckling modes are found, as well the stability regions in the planes of the loading parameters. The detailed analysis of the size effect, as well as the influence of mechanical properties and coating thickness, on the equilibrium bifurcation is carried out for an elastic composite rod of micropolar material subject to combined loads.
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