Hardening-softening behaviour of tubular cantilever beams

In the large plastic deformation of a tubular cantilever beam loaded by a force at its tip, the strain hardening of the material tends to increase the load-carrying capacity, while local buckling and cross-sectional ovalization (flattening) occurring in the neighbourhood of the root tends to reduce the moment-carrying capacity and results in structural softening. Experiments were carried out for seamless mild steel tubular cantilevers of radius/thickness ratio ranging from 9 to 20 to explore the development of local buckling and flattening and to examine its influence on the global load-carrying capacity of the beam. A simple theoretical model is proposed to predict the global hardening-softening behaviour of tubular cantilever beams in terms of the material properties and geometric parameters of the tube.