Study on Hot Spot Stress Calculation for Welded Joints using 3D Solid Finite Elements Oh, Jung-Sik; Kim, Yooil; Jeon, Seok-Hee;
Because of the high stress concentration near the toe of a welded joint, the calculation of local stress using the finite element method which is relevant to the fatigue strength of the weld toe crack, is a challenging task. This is mainly caused by the sensitivity of finite element analysis, which usually occurs near the area of a dramatically changing stress field. This paper presents a novel numerical method through which a less mesh-sensitive local stress calculation can be achieved based on the 3D solid finite element, strictly sticking to the original definition of hot spot stress. In order to achieve the goal, a traction stress, defined at 0.5t and 1.5t away from the weld toe, was calculated using either a force-equivalent or work-equivalent approach, both of which are based on the internal nodal forces on the imaginary cut planes. In the force-equivalent approach, the traction stress on the imaginary cut plane was calculated using the simple force and moment equilibrium, whereas the equivalence of the work done by both the nodal forces and linearized traction stress was employed in the work-equivalent approach. In order to confirm the validity of the proposed method, five typical welded joints widely used in ships and offshore structures were analyzed using five different solid element types and four different mesh sizes. Finally, the performance of the proposed method was compared with that of the traditionally used surface stress extrapolation method. It turned out that the sensitivity of the hot spot stress for the analyzed typical welded joints obtained from the proposed method outperformed the traditional extrapolation method by far.
Hot spot stress;Fatigue;Welded joint;Nodal force;Traction stress;
ASME, 2013. ASME Boiler and Pressure Vessel Code Section VIII Division 2. The American Society of Mechanical Engineeris, New York, NY.
Bathe, K.J., 1982. Finite Element Procedures in Engineering Analysis. Prentice-Hall, New Jersey.
Doerk, O., Fricke, W., Weissenborn, C., 2003. Comparison of Different Calculation Methods for Structural Stresses at Welded Joints. International Journal of Fatigue, 25, 359-369.
Dong, P., 2001. A Structural Stress Definition and Numerical Implementation for Fatigue Analysis of Welded Joints. International Journal of Fatigue, 23, 865-876.
Dong, P., 2004. The Mesh-insensitive Structural Stress and Master S-N Curve Method for Ship Structures. Proceedings of OMAE Specialty Conference on Integrity of FPSO System, Houston, USA.
Healy, B.E., 2004. Hot Spot Stress Analysis of a Side Shell Connection using Surface Extrapolation and the Batelle Structural Stress Method. Proceedings of OMAE Specialty Conference on Integrity of FPSO System, Houston, USA.
Niemi, E., 1992. Recommendations Concerning Stress Determination for Fatigue Analysis of Welded Components. IIW Document IIW-1458-92/XV-797-92, International Institute of Welding.
Gurney, T.R., 1984. Fatigue of Welded Structures. Cambridge University Press, Cambridge, UK.
Hobbacher, A., 2004. Recommendations for Fatigue Design of Welded Joints and Components. IIW Document XIII-1965-03/XV-1127-03, International Institute of Welding.
Lotsberg, I., 2004. Recommended Methodology for Analysis of Structural Stress for Fatigue Assessment of Plated Structures. Proceedings of OMAE Specialty Symposium on Integrity of FPSO System, Houston, USA.
Poutiainen, I., Tanskanen, P., Marquis, G., 2004. Finite Element Methods for Structural Hot Spot Stress Determination a Comparison of Procedures. International Journal of Fatigue, 26, 1147-1157.