Modelling and fatigue life assessment of complex structures

This paper presents some of the motivations and main conclusions from a series of joint Nordic research initiatives in which an integrated research approach to the development of future generations of advanced fabricated structures have been employed. The integrated research approach includes coordinated efforts in several key technologies: high-speed welding processes, high strength materials, cost-effective NDE, post-weld treatments and FE-based design assessment tools. Traditionally, fatigue assessment methods for welded structures have been developed based on small-scale test specimens and verification studies for large structures are rarely published. Applications on complex structures have led to several new assessment concepts and areas for future work. A modified structural stress method that proposes a multi-linear stress distribution through the plate thickness is introduced. Also, a crack growth assessment method in which the constraint equations of a sub-model are linked to the global model is presented. Both these new methods are promising for complex structures. The crucial role of boundary conditions for complex structures is highlighted as is the future challenge of understanding and making use of the residual stress state for welded structures.