Cyclic material behaviour of welded ultra high-strength steels

A crucial issue within the field of crane structures is the fatigue life of welded ultra high-strength fine-grained steels, which are widely used in order to achieve increasing carrying capacities and to enable lightweight design. The typical fatigue behaviour of highly loaded truck and crawler cranes is related to the low cycle fatigue (LCF) regime and often focused on critical details of welded joints. Fatigue recommendations for the design and analysis of welded structures [1, 2] are based on fatigue resistance Wöhler curves irrespective of the steel grade and describe the LCF behaviour improperly. Latest stress-controlled experiments on large scale, butt-welded specimens describe the overall S-N relation of such structural elements in the LCF and HCF regime [3], but do not describe the mechanisms leading to fatigue of welded ultra high-strength steels accurately - especially in case of variable amplitude loading.