A method of determining geometric stress for fatigue strength evaluation of steel welded joints

This paper presents a new method for evaluating the geometric or structural stress in welded constructions. The method is based on the computed stress value 1-mm below the surface in the direction corresponding to the expected crack path. The total stress distribution along the crack path direction is considered to be the sum of the geometric stress caused by the structural geometry change and the non-linear local stress produced by the weld itself. Linear elastic fracture mechanics is used to correlate the total stress based crack propagation life and the local stress based crack propagation life to explain the geometric stress evaluated 1-mm below the surface. Validity of the method is further verified by analyzing fatigue test results for several typical welded joints reported in literature. When compared to the surface extrapolation technique for structural hot spot stress evaluation, the proposed method has the additional advantage in that it is able to account for the size and thickness effect observed in welded joints.