Study Of Multiaxial Fatigue Life Prediction On Welded Structures In Naval Architecture And Ocean Engineering

In the naval architecture and ocean engineering field, most of the weldments are subjected to multiaxial fatigue loading. There exist three aspects causing to the multiaxial fatigue failure of weldments:the complicated fatigue loading and geometries of weld toe, and the welding residual stresses, which lead a multiaxial stress state in local area of weldments. However, most of the time, the theory of uniaxial fatigue life prediction are used to give a conservative prediction on the weldments according to the classification society rules, which usually leads a dispersive prediction. An amount of research results have showed that, the multiaxial fatigue theory is fundamentally different from the uniaxial fatigue theory, and the traditional uniaxial fatigue theory is not able to meet the demands of multiaxial fatigue life prediction of complicated weldments anymore.At present, there is little multiaxial fatigue assessment method in rules and regulations. Although variety of multiaxial fatigue life assessment methods are proposed in international, there is little method applicable to the actual complicated weldments, especially to the welded offshore structures. The main reason is that the existing methods are difficult to deal with the complex and changing stress state in weld toe. In addition, most of the current methods are focus on the multiaxial fatigue loading, but less focus on welding residual stress.This article used the point where the nonlinear peak stress reaches zero as the fatigue life assessment point (named zero point). It can directly calculate the complex stress state in weld toe, and can be used in the multiaxial fatigue assessment. The effectiveness of the proposed method is verified by the theoretical analysis and numerical calculation. Results indicate that the proposed approach is more accurate than traditional hot spot stress method. At last, this article proposed a new multiaxial fatigue criterion which can consider the welding residual stresses effectively. The multiaxial fatigue experimental data containing the welding residual stresses was chosen to verify the proposed approach. Results indicate that the new creation is able to consider the residual stresses effectively, and it is more accurate than MWCM.