Research On Fatigue Properties And Life Prediction Of Ring Welding Joints For Stainless Steel Carbody

The stainless steel carbody has the advantages of light-weight, high-strength, long service life, economy, etc., therefore, much attention was paid to the research and application of it in china and overseas. The main welding methods of stainless steel carbody contain spot welding, ring welding, plug welding, etc. Due to the structure features, large stress concentration at welding position can induce the fatigue failure. For the stainless steel carbody, the number of ring welding spot accounts for a large percentage of all the spots, so the fatigue life of ring welding joint has significant effect on the service life of carbody. However, there is little research on fatigue performance of ring welding at home and abroad, so it is urgent to conduct this research.In this paper, the fatigue tests were carried out on RUMUL high-frequency fatigue test machine with the ring welding specimens of stainless steel plate. The loading-life (△Fa-N) data were obtained and the fracture surfaces were observed by SEM. The fracture characteristics and crack growth rule were analyzed and a fatigue life prediction method for ring welding joints was proposed based on the fracture mechanics. The effects of pore size, welding hole position, average loading and bending degree on fatigue properties of ring welding joints were clarified. The main conclusions are given as follows:The cracks of two welded plates initiate from arc head along loading direction of ring welding specimens, where the stress concentration is the biggest. The fatigue cracks at welding-hole plate and non-welding-hole plate propagate from welding roots to external along the direction of plate thickness and then to the base metal along arc direction, finally it propagate transversely within the base metal. The crack propagation life in the weld metal of welding-hole plate accounts for more than90%of the total life. Therefore, the fatigue life can be increased by improving the fatigue strength of weld metal. The fatigue prediction method was proposed and it was verified by the application of ring welding specimens with three types for different pore sizes and thickness. It is found that the predicted results show the same trend with test result and they meet the application demand of optimization design for engineering structure. The analysis of test results show that:the fatigue life increase with the increase of pore size; the welding hole position of welded plate with different thickness has little effect on fatigue life; the average load can reduce the fatigue life; the bending phenomenon of welded plate during the test can significantly reduce the fatigue life.