Specimen design for gigacycle fatigue testing of structural steel welded joints

Structures and components across a range of industries exhibit service lives above 107 cycles, but there is limited fatigue data in this domain. Conducting fatigue tests in the gigacycle regime is only feasible by using ultrasonic fatigue testing machines in which specimens are typically excited at 20 kHz. This research focuses on the design of a novel specimen which captures the geometric stress concentration at the weld toe, as an alternative to typically used cylindrical ‘hourglass’ shaped specimens. The gas-shielded flux-core arc welding method was used to manufacture butt joints of 080A15 structural steel. Specimens were tested in fully reversed axial loading at room temperature using a Shimadzu USF-2000A ultrasonic fatigue testing machine. Specimens failed in the range of 104-107 stress cycles with all fatigue cracks initiating at the weld toe. One specimen was classed as a run-out after being subjected to 3 × 109 stress cycles without failure. The fatigue data obtained was assessed using the effective notch stress method and showed similar fatigue performance to the IIW guidelines.