Issue34

K.L. Yuan et alii, Frattura ed Integrità Strutturale, 34 (2015) 476-486; DOI: 10.3221/IGF-ESIS.34.53 485 a) b) Figure 14: (a) Validation of the predicted fatigue life of the as-weld and UIT joints, (b) Predicted evolution of surface crack shapes. C ONCLUSIONS ased on the existing experimental observations, a model describing the ultrasonic impact phenomenon is proposed in this paper. Employing commercial codes SYSWELD and LS-DYNA, a three dimensional numerical simulation approaches for UIT-improved welded joints is established, of which the effectiveness has been well validated by comparing with experimental results. From the numerical results, it has been verified that UIT is an effective method to re-distribute the residual stress and reduce the stress concentration near the weld toe area. Deformation and compressive residual stress layer are more pronounced when acoustic softening occurs, which is necessary to be considered in numerical simulation. A CKNOWLEDGEMENTS he authors are grateful to Professor Y. Kawamura, Yokohama National University, Dr. H. Shimanuki and Dr. T. Okawa, Nippon Steel & Sumitomo Metal Corporation, for their helpful discussions. R EFERENCES [1] Galtier, A., Statnikov, E., The influence of ultrasonic impact treatment on fatigue behavior of welded joints in high- strength steel, Weld World, 48 (5-6) (2004) 61-66. [2] Cheng, X.H., Fisher, J.W., Prask, H.J., Gnäupel-Herold, T., Yen, B.T., Roy, S., Residual stress modification by post- weld treatment and its beneficial effect on fatigue strength of welded structures, Int J Fatigue, 25(9) (2003)1259-1269. [3] Okawa, T., Shimanuki, H., Funatsu, Y., Nose, T., Sumi, Y., Effect of preload and stress ratio on fatigue strength of welded joints improved by ultrasonic impact treatment, Weld World, 57(2) (2013) 235-241. [4] Marquis, G.B., Mikkola, E., Yildirim, H. C., Barsoum, Z., Fatigue strength improvement of steel structures by high- frequency mechanical impact: proposed fatigue assessment guidelines, Weld World, 57(6) (2013) 803-822. [5] Marquis, G.B., Barsoum, Z., Fatigue strength improvement of steel structures by high-frequency mechanical impact: proposed procedures and quality assurance guidelines, Weld World, 58(1) (2014) 19-28. [6] American Bureau of Shipping, Commentary on the guide for the fatigue assessment of offshore structures (2014). [7] Polezhayeva, H ., Howarth, D., Kumar, M., Kang, J. K., Ermolaeva, N., Lee, J.Y., Effect of ultrasonic peening on fatigue strength of welded marine structures-Lloyd’s Register Research Programme., Proc. 24th ISOPE Conference, (2014) 359-365. [8] Weich, I., Edge layer condition and fatigue strength of welds improved by mechanical post-weld treatment, Weld World, 55(1-2) (2011) 3-12. B T