Fatigue behaviors of aluminum alloy butt joints with backing plates: Experimental testing and traction stress modeling

• The fatigue properties and failure modes of butt joints with backing plates are studied by conducting fatigue tests and UPAT. • A method for predicting failure modes of butt joints with backing plates is proposed. • The fatigue performance of butt joints with backing plates is evaluated based on the IIW and BS7608 standards. • The effect of angular misalignment on the failure modes of test specimens is investigated. • The effect of failure modes on the fatigue properties of the test specimens is studied. In this study, the fatigue behaviors and associated failure modes for a series of aluminum alloy butt joints with backing plates are investigated by conducting fatigue testing and Ultrasonic Phased Array Testing (UPAT). When the fatigue properties of butt joints are evaluated according to International Institute of Welding (IIW) and BS7608, the S-N curves of the corresponding welded joints cannot be determined due to irregular positioning of tack welds prepared, following typical manufacturing practices. To gain insights on how the fatigue test data can be correlated with different backing plate positions, traction structural stress method is used for determining both critical fatigue-critical location and corresponding stress value in the test specimens. It is found that the traction stress method is effective in identifying fatigue-critical location caused by backing plate welds and incorporating angular joint misalignment effects.