Effect of Welding Flaws on the Fatigue Life of High Strength Steel Structures

The use of a welded high strength low alloy steel for an aerospace application involving high cycle fatigue was investigated. Welded specimens were fabricated and investigated under static and dynamic loading. The fatigue behavior of welded specimens was shown to vary significantly from unwelded specimens as expected, but also varied based on the type(s) of welding flaws detected by radiography. LEFM principles and crack growth parameters from steels with similar microstructures were used to model fatigue crack propagation in specimens with sharp flaws. The model was able to reasonably predict the fatigue life for these specimens. After the model was calibrated, specimens with internal pores were also studied in order to separate regimes of crack initiation and propagation during the fatigue lifetime. In specimens with only porosity flaws, the mean initiation life was over 60% of the total fatigue life, showing the benefit of removing sharp flaws from welds.