Ultra-low Cycle Fatigue Fracture of High-Strength Steel Q460C and Its Weld

In order to investigate the ultra-low cycle fatigue (UCLF) fracture in welded connections of high-strength steel (HSS) under earthquakes, this paper studies micromechanical fracture models for Q460C steel, which has wide application prospects in China. Notched round bars and smooth round bars, which were manufactured from base metal, heat-affected zone (HAZ), and weld metal of Q460C HSS, were tested under monotonic loading and cyclic loading, respectively. The fracture surface of tensile specimens were analyzed by scanning electron microscope (SEM) tests. This paper presents the results, including the skeleton curve, hysteresis loops, low cycle fatigue life, and characteristic length l. By comparing the experimental results with the finite-element analyses, the toughness parameters of the void growth model (VGM), the stress-modified critical strain (SMCS) model, and the cyclic void growth model (CVGM) of Q460C HSS and its weld were calibrated. Results indicate that the toughness parameters of various materials for HSS are generally lower than that of normal strength steel. Also, in the welded beam-to-column connections, the HAZ requires more attention. The results can be used to effectively and accurately evaluate the UCLF fracture in welded HSS connections.