Applying the Cyclic Void Growth Model to Assess the Ultralow Cycle Fatigue Life of Steel Castings

Abstract

Steel castings have become an attractive option in the development of new seismic force-resisting systems because of their geometric freedom and ability to control material properties. Despite, in most past applications, being used as elements that remain elastic during seismic events, recent research has led to the development and validation of new systems that rely on their yielding response. As such, further study of their ultralow cycle fatigue (ULCF) life is essential to understanding their performance as yielding fuses. Fatigue laws are calibrated herein for multiple heats of cast steel using an existing law proposed for rolled steel. These laws are used to predict the ductile failure of steel castings in full-scale experiments. The concept of a characteristic cyclic coupon test to assess the castings’ ULCF life at the foundry is also discussed. It is found that the ULCF model provides good predictions of the onset of failure in full-scale steel castings. Finally, the initial investigation into relating the full-scale ULCF life to the steel microstructure and small-scale fatigue test results has shown promising results.