Study on elastoplastic pure bending collapse of cylindrical tubes with consideration of the length effect

In this paper, the elastoplastic collapse of a cylindrical tube subjected to pure bending is studied by using the finite element method. There exist two types of collapse : a collapse due to buckling at the compression side and a collapse due to flattening of the cross-section. In the flattening collapse, the maximum bending moment is controlled by the flattening rate of the tube cross-section. For a short tube, the boundary condition of the fixed walls at the both ends prevents the flattening development. A theoretical prediction method of the flattening rate and the maximum bending moment of cylindrical tubes subjected to pure bending is proposed, in which the effect of the tube length is taken into account. In the method the flattening is simulated by a deflection problem of a beam based on distributed springs. The validity of the proposed method is verified by numerical results of FEM.