Effect of cold bending and welding on buckling of ring-stiffened cylinders

Abstract

The BOSOR5 computer program for elastic plastic buckling of shells of revolution is used for calculation of bifurcation buckling of cold bent and welded ring-stiffened cylinders under external pressure. Residual stresses and deformations from cold bending and welding are included in the model for buckling under service loads by introduction of these manufacturing processes as functions of a time-like parameter which ensures that the material in the analytical model experiences the proper sequence of loading prior to and during application of the service loads. The cold bending process is first simulated by a thermal loading cycle in which the temperature varies linearly through the shell wall thickness, initially increasing in time to simulate cold bending around a die and then decreasing in time to simulate springback to a final somewhat larger design radius. The welding process is subsequently simulated by the assumption that the material in the immediate neighborhoods of the welds is cooled below the ambient temperature by an amount that leads to weld shrinkage amplitudes typical of those observed in tests. Buckling loads are calculated for a configuration including and neglecting the cold bending and welding processes. These predictions are compared to values obtained from tests on two nominally identical specimens, one carefully machined and the other fabricated by cold bending the shell and then welding machined ring stiffeners to it.