Ductile Fracture Model of Structural Steel under Ultra-low-Cycle Fatigue Loading

Abstract

For specimens under ultra-low-cycle fatigue loading, cyclic plasticity and negative stress triaxialities are two main differences from monotonic loading cases. In this chapter, a crack initiation rule by adding a damage accumulation rule under negative stress triaxialities is proposed, where no damage accumulation is assumed for stress triaxialities below −1/3. This rule is based on previous experimental results. This chapter is mainly focused on the crack initiation rule of ductile metal under ultra-low-cycle fatigue loading (ULCF). Likewise, crack propagation is assumed to occur once a crack initiates. The cyclic ductile fracture model is validated through comparison with cyclic tests on hourglass-type specimens under a series of different loading histories. Numerical fracture simulation using both the previously proposed cyclic plasticity models and the cyclic ductile fracture model is conducted, and the analysis can well predict ductile cracking of the specimens with relatively uniform stress and strain distribution.