Fatigue Evaluation Procedures for Multiaxial Loading in Welded Structures Using Battelle Structural Stress Approach

The Battelle structural stress method is examined for the evaluation of multiaxial loading fatigue behavior in welded structures. Even though the structural stress and its master S-N curve approach have been mainly focused on normal loading dominant (Mode I) failure cases, the evaluations on multiaxial loading weld fatigue using structural stress parameters have been relatively recently performed such as using the modified Gough ellipse [1] and the path-dependent maximum range (PDMR) cycle counting procedure [2].In this article, in order to evaluate the multiaxial fatigue behavior, an effective equivalent structural stress range (EESS) parameter is defined as a von Mises form of combined normal and in-plane shear equivalent structural stress ranges. The newly developed in-plane shear equivalent structural stress range for in-plane shear dominant loading (Mode III) is introduced. This in-plane shear equivalent structural stress range parameter has been formulated based on the evaluation of fatigue behavior under in-plane shear loading. Also, the EESS parameter is a function of damage parameter based on the PDMR procedure.In this article, the procedure employing the EESS parameter is evaluated and validated using published weld fatigue data. The multiaxial fatigue date is consolidated within a small scatter band regardless of in-phase, out-of-phase, and non-proportional loading as well as torsional loading. Finally, the design master S-N curve is proposed for multiaxial loading weld fatigue.It is found that the dimensionless bend ratio parameter, Iτ (rτ)1/mτ for in-plane shear loading is a much more significant correction than that for normal loading when the ratio of bending structural stress to the total structural stress, rτ increases. This procedure will be beneficial for fatigue design with preventing over-conservatism.Copyright © 2014 by ASME