Objectives  Q690 high strength steel (HSS) is usually employed in the fabrication of special parts for semi-submersible lifting and dismantling platforms. As such, the fracture strength assessment of its welded joints is essential to an investigation of the fracture mechanics behavior and service life of offshore structures.

  Methods  First, the base material and butt-welding joints of Q690 HSS are taken as the research objects and subjected to uniaxial tension tests to obtain the corresponding stress-strain curves. Next, based on the GTN damage model, the tensile fracture curve equations of Q690 HSS and its butt-welded joints are established, while the corresponding calculation parameters of the GTN model are obtained through the exhaustive and particle swarm methods.

  Results   The results show that the optimized values of the GTN model parameters can generally evaluate the fracture performance of Q690 HSS and its butt-welded joints, while a heuristic search algorithm based on the particle swarm method can effectively improve search efficiency with sufficiently accurate GTN model parameters.

  Conclusion  Welding induced micro-defects and residual stress are eventually proposed to illustrate the difference in fracture performance between Q690 HSS and its butt-welded joints, which also influences the variation tendency of the GTN model parameters.