Introduction and objectives
This chapter gives an overview of fatigue behavior of welded joints. The basic mechanisms of the fatigue damage process are discussed and the usual method and models for fatigue life verification are outlined. The basic parameters that are important for the fatigue process in welded joints are pinpointed. The objective of the chapter is to give the reader basic insight into the fatigue process in welded joints, with emphasis on the aspects that makes these joints vulnerable to fatigue. The reader will be acquainted with the most common methods and models for describing the fatigue problem. These methods will be elaborated further in Chapters 5 and 6 where the S-N model and the facture mechanics approach are described in more detail.
2.2. Fatigue failures
Fatigue is defined as damage accumulation due to oscillating stresses and strains in the material. Therefore, fatigue cracks do occur in welded details that are subjected to repetitive loading. In significant structural items they may lead to failures with severe consequences. The Health and Safety Executive, UK, has listed the main causes of structural damage for installation in the North Sea (1974-1992, Ref [1]) as:
– fatigue 25% – vessel impact 24%