  When a soft elastic cylinder is bent beyond a critical radius of curvature, a
sharp fold in the form of a kink appears at its inner side while the outer side
remains smooth. The critical radius increases linearly with the diameter of the
cylinder while remaining independent of its elastic modulus, although, its
maximum deflection at the location of the kink depends on both the diameter and
the modulus of the cylinders. Experiments are done also with annular cylinders
of varying wall thickness which exhibits both the kinking and the ovalization
of the cross-section. The kinking phenomenon appears to occur by extreme
localization of curvature at the inner side of a post-buckled cylinder.
