Fatigue Performance of Cracked Tubular T Joints under Combined Loads. I: Experimental

Experimental fatigue tests were carried out on three tubular T joints having the same geometrical parameters subjected to in-plane bending (IPB) only, combination of IPB and out-of-plane bending (OPB), and a combination of axial loading, IPB and OPB respectively. Static tests were first carried out to investigate the Hot Spot Stress (HSS) distribution along the intersection of chord and brace, and to determine the peak HSS and its location when the joints were subjected to these load cases. The peak HSS location was used to determine the placement of the probes. An alternating current potential drop technique was then employed to monitor the crack growth and crack shape development on the joints at a preset number of cycles. The experimental data were recorded, and the fatigue performance of the three T joints subjected to basic and combined load cases were investigated. The crack growth curves and crack growth rate on each specimen were presented. The results confirmed that the United Kingdom Department of Energy tubular joint fatigue design T curve derived from a single axis test data is conservative even for combined load cases.