Torsional buckling of elastic cylinders with hard coatings

The torsional buckling characteristic of an elastic cylinder with a hard surface coating layer is addressed in this paper. Deformations of the core and surface layer are obtained analytically through the Navier's equation and thin shell model, respectively. Both infinitely and finitely long cylinders are studied and the effects of the surface layer's stiffness, thickness, residual stresses, as well as the cylinder lengths on the critical torsional angle and buckling morphologies, are discussed. It is found that either the surface rippling or global buckling mode may occur when there exist residual stresses within the surface layer. The critical torsional angle increases when the surface layer becomes stiffer and thinner. In addition, higher-order rippling modes frequently occur for a finite-length cylinder with stiffer and thinner surface layer.