Hot Spot Stress Method For Welded Structures Based On Self-balancing Nonlinear Stress Peak

Fatigue is one of the major failure modes in ship and offshore structures. So far, fatigue has been considered to be a hot and difficult problem. On the one hand, compared with the uniaxial fatigue, multiaxial fatigue is closer to engineering practice and obtains a strong support from the engineering. On the other hand, it enriches people's understanding of fatigue damage and failure process, and also attracts great attentions from the academia.When we evaluate the multiaxial fatigue life, the size and direction of stress components of welded structures is difficult to control and obtain through the reference point of stress components by extrapolation actually. However, the current hot spot stress method only considers structures'surface stress. But it ignores the affection of stress gradient along plate-thickness's direction on the fatigue strength.Considering the problems of the hot spot stress method for evaluating multiaxial fatigue strength of complex welded structures, a new hot spot stress method is proposed to solve these problems from the engineering point of view.Firstly, finite element analysis is performed to obtain the discipline of the stress distribution through the plate thickness using butt welds.Secondly, finite element method is investigated for the calculation of the stress field near the point where the value of nonlinear stress peak is zero.Finally, Finite element models of several typical structures are analyzed. By comparing with the results calculated from the traditional method and obtained from fatigue tests, the accuracy of the proposed method is verified.The new method needs no linear extrapolation, and also considers the influence of the stress gradient through plate thickness on fatigue strength, and the calculated hot spot stress can be used ditectly for the multiaxial fatigue evaluation of welded structures.