Fatigue Properties Evaluation Considering Welding Residual Stress On Welding Joints

Steel Bridge is an important component of the bridge development process, whose fatigue failure has been an important aspect of the bridge study. Welding will produce a greater stress concentration, which is easy to make material to yield to influence the stiffness of the structure. The structure will be destroyed under stress limit in a dynamic load, so the study of stress distribution in the welding process and welding on fatigue is important for the safety of the bridge.Welding is a complex process involving physics and chemistry, which need the theoretical calculations combined with the actual measurements. Welding residual stress generates mainly composed of two parts:the plastic deformation stress and phase transformation stress. The phase transformation stress can be ignored in a material with high phase transition point. Plastic deformation stress can be determined relying on the numerical simulation of heat and force. We can obtain the distribution of welding residual stress with the numerical simulation, and determine the actual welding residual stress distribution and size with the actual measure. In the study of steel fatigue, the welding residual stress is computed as one part of mean stress. The influence of the relaxation of welding residual stress to stress amplitude in the plastic deformation of alternating stress is generally ignored.In this thesis, the typical welding cross joint and fatigue crack with reference of experiment is simulated by ANSYS finite element software. The fatigue design considering welding residual stress as one part of mean stress is also evaluated in this thesis. This thesis mainly included following aspects:1 This thesis obtains the temperature and stress distribution through simulating the welding cross joint in four different angle of long and short board by ANSYS. The peak temperature mainly distributes in the part contacted with more atmospheres. The peak stress mainly distributes in welding toe and welding root. As the reduction of the angle of long and short board the welding residual stress is mostly reducing and partially (long board direction in welding root) increasing slowly.2 This thesis obtains the change of welding residual stress in the development of fatigue crack through simulating the experiment crack by ANSYS. The welding residual stress in the part of crack is mostly reducing with crack development. As the reduction of the angle of long and short board the welding residual stress is still reducing.3 This thesis suggests and proves one new fatigue damage parameter considering welding residual stress and mean stress, which considering the plastic deformation, stress limit and welding residual stress is different from the fatigue design at present and will promote the fatigue study.