PSI - Issue 22

Xiaoteng Wang et al. / Procedia Structural Integrity 22 (2019) 59–63 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

63

5

surface. As well known that crack is found easier in the area with high stress concentration. That is to say, with the decrease of reinforcement of welding surface, the fatigue life of welding joints is longer. And the fatigue life of welding joints with smoother welding toe is longer. To find out the how the fatigue crack occurs and grow, the fracture surface is observed with electron microscope, which is shown in Figure3. Figure3 (a1) and (b1) is fatigue facture surface of welding joints of GMAW and HPAW, and the Figure3 (a2) and (b2) is the partial enlarged view of (a1) and (b1). The reasons of the fatigue life of welding joints with HPAW being longer than those of GMAW can be concluded as follows. First and foremost, the proportion of crack origin (shown with red dashed line), crack extension area (shown with yellow dashed line) and interruption area (the other parts) is different with different welding method. And the proportion of interruption area with GMAW is larger than those of HPAW, which cause the crack propagation rate of welding joints with GMAW is larger than those of HPAW. Therefore, the sample of welding joint with GMAW is prone to fracture. Secondly, the crack origin of welding joint with GMAW is nearly welding seam, but those of HPAW is nearly base metal. That is to say, at the same stress of 340MPa, the welding joint of GMAW because of greater stress concentration in the welding toe is easier to facture in comparison with those of HPAW. Last but not least, as shown in Figure3 (a1), the sample of GMAW factures from three crack origin, but the sample shown in Figure3 (b1) of HPAW factures only one crack origin. It is worth mentioned that in Figure2 (a1) the interruption area is not continuous, occurring two parts of different area. The reason of this phenomenon is that with the process of experiment, the distance of two parts of sample is too short to cause the sample fracturing. 4. Conclusion From the experimental results and discussions, it can be concluded as the following: (1) The high strength steel can be welded with GMAW and HPAW. Compared with GMAW, the fatigue life of HPAW can increase 62.7%. And in the 95% confidence interval, the fatigue life of welding joints with HPAW increased from 30.28% to 93.78% than those of GMAW Furthermore, the reinforcement of HPAW is lower, and the welding toe is smoother. (2) Because of the different proportion of crack origin, crack extension area and interruption area, as well as the different position of crack origin, the fatigue life of welding joint with HPAW is longer than those of GMAW.

References

[1] Dykhno I. & Davis R. Joining GMAW and GTAW. The Fabricator. November 2006, 60-62. [2] Zhentong Gao, Junjiang Xiong, Fatigue reliability. December 2000, Beijing University of aeronautics and astronautics press, Beijing.