Low Cycle Fatigue Evaluation for High Strength Welded T-Joint Based on Structural Strain Method

Abstract

Abstract In design process of welded structures, fatigue failure is one of the main issues to be carefully considered in the assessment of the structural integrity. In general, fatigue failure typically occurs at locations structural discontinuities. In particular, welded structures inevitably contain structural discontinuities during manufacturing process and those locations are vulnerable to fatigue loads. The 2007 ASME Div.2 Code suggests a master S-N curve approach based on structural stress that is insensitive to the size of element with improved accuracy in stress calculation [1]. Structural stress method has been validated based on numerous experimental data and studies in the high-cycle fatigue regime. However, these methods cannot be applied in low-cycle fatigue regime, and validations of the structural stress method in the low-cycle regime are insufficient so far. In this regard, an extension to the master S-N curve, structural strain method was introduced to evaluate the low-cycle fatigue performance by Dong et. al [2]. The target of this study is to validate the structural strain method in low-cycle fatigue regime of welded joints. For that purpose, low-cycle fatigue test was performed on high strength steel welded T-joints. Pseudo structural stress can be calculated through the derived structural strain, and the equivalent structural stress is expressed in consideration of the shape and thickness effects. Fatigue life evaluation using structural strain method exhibited a good correlation with the master S-N curve not only in the elastic region but also in the low-cycle regime accompanied by plastic deformation. By using structural strain method, it is possible to comprehensively evaluate the fatigue life both in high and low-cycle fatigue regime.