An Analytical Model for Predicting the Fatigue Behavior of Tubular Weldments Subjected to Compressive Loading

It has been well-documented in academic literature that, when subjected to compressive cyclic loading (R = -∞), weldments can experience fatigue failure. However, unlike non-welded components, it has been shown that mean stress has a negligible impact on the fatigue life of welds (Gurney, 1979). Currently, most analytical weld prediction methods neglect the influence of mean stress and instead focus only on the relationship between the stress (or strain) amplitude and the respective number of cycles to failure. To better understand the influence of compressive mean stress on tubular weldment fatigue life, three case studies were performed under varying loading conditions: 1) Welds were subjected to compressive pre-stress using pretensioned bolts and then subjected to various cyclic loading conditions via three-point bending, 2) Welds without pre-stress were subjected to various cyclic loading conditions intended to generate compressive mean stress in the welds via three-point bending, 3) Welds without pre-stress were subjected to various cyclic loading conditions intended to generate a stress state of pure tension or pure compression in the welds via four-point bending. It was observed that tubular weldments (e.g. an axle tube with a welded bracket) subjected to compressive loading exhibited significant resistance to fatigue failure. Analytical fatigue predictions of the three aforementioned case studies using the Structural Stress Method, which has been demonstrated to be a very effective method for predicting the fatigue life of welded structures, yielded life predictions that were considerably lower than the tested weldments. This paper proposes an analytical model for predicting weldment fatigue life which uses an improved Structural Stress approach that considers the influence of compressive mean stress.