Residual stress effects in tubular K-joints crack growth

Seeking light and transparent bridge designs, engineers and architects have found an efficient and artistic way to fulfill their requirements: steel tubular bridges. Like any other welded structure, the joints of this kind of bridge suffer from high tensile weld residual stresses. Combined with high stress concentrations, tensile residual stress is a relevant factor in fatigue crack development. Therefore, an experimental study has been carried out on tubular joints in order to characterize the 3D residual stress field, using mainly the Neutron Diffraction method. On the other side, two large-scale welded tubular truss beams were tested under constant amplitude fatigue loading. It is revealed that the peak tensile residual stress, exceeding the yield stress of the material, is localized at ~2 mm under the surface and allows cracks to develop in compressive joints. The influence of residual stresses on stable crack propagation is analyzed based on fracture mechanics theory.