Enhancement of the fatigue strength assessment of welded components by consideration of mean and residual stresses in the crack initiation and propagation phases

The starting point of the investigations presented in this paper is the simplified consideration of mean and residual stresses as well as the complete disregard of the complex failure mechanisms in the common fatigue standards and guidelines. An improved fatigue life assessment for welded components, which includes the crack initiation and propagation phase is the scope of this paper. The crack initiation phase is considered using the strain-life approach. The crack propagation life, starting from a technical crack of a depth of a = 0.5 mm, is derived by the application of linear-elastic fracture mechanics. In this two-phase approach, the mean and residual stresses are considered by using damage parameters for the initiation phase and effective stress intensity factors for the propagation phase. With this approach, a better understanding can be obtained of the influence of mean- and residual stresses and their influence on the course (slope k and knee point N-k) of the S-N curve. With this information to hand, a more reliable fatigue assessment can be achieved than is possible with the common standards and guidelines. With the proposed two-phase approach, higher permissible stresses can be allowed in the design phase, leading to resource-efficient, lightweight constructions.