Study on the Effect of Permanent Backing on the Fatigue Performance of Butt Welded Joints

The butt weld groove joint is a predominant joint type in box structures such as bogie welded frameworks, railway freight car center beams, specialized railway vehicles, and cranes. The quality of these welds significantly affects the performance of these structures. In accordance with the GB/T13816-92 standard, which outlines the test methods for fatigue under pulsating tensile loads in welded joints, a pulsating tensile fatigue test was conducted on five types of joints, including single-sided welds with double-sided formation, ceramic backing, and permanent backing. The microstructure of the fatigue fracture surfaces was analyzed using a JSM-6360LV scanning electron microscope （SEM） to investigate the effect of permanent backing on the fatigue performance of the joints. The results indicate that butt joints with permanent backing, combined with fillet weld tack welding, exhibited superior fatigue resistance compared to other configurations. Moreover, the initial crack location in the welds was significantly influenced by different tack welding methods, providing valuable insights for selecting appropriate welding techniques in practical engineering applications.