On the analysis of cylindrical tubes under flexure: theoretical formulations, experimental data and finite element analyses

In the present paper the behaviour of cylindrical elastic tubes under pure bending is discussed. This behaviour is characterised by a smooth global maximum on the load-deflection curve which is due to the well-known von Kلrmلn effect, that is to the progressive flattening of the cross section of the tube under bending moment. However, during the loading process another type of failure may also occur before the limit load is reached, that is, at a certain stage the compressed region of the bent tube wrinkles axially and can give origin to a localised instability. Even if these phenomena have been extensively investigated in many classical works, nevertheless the analysis of experimental data shows that there are still some points which seem to be worthy of further considerations, especially from an engineering standpoint and for design purposes. To this aim, a straightforward treatment of the problem is presented which can be employed to give clear reason for several experimental findings by means of plain expressions and with a clear physical meaning. Finally, the results are compared to those obtained by means of a commercially available non-linear finite element code.