Henry Granjon Prize Competition 2009 Winner Category C: “Design and Structural Integrity” EDGE Layer Condition and Fatigue Strength of welds improved by mechanical post-weld treatment

Abstract

In this paper, investigations about the beneficial effect of high frequency peening methods on the fatigue strength of welds are reported. Recent investigations prove that these methods are effective means of improving the fatigue strength of welded details. In the reported studies, the mode of functioning of these methods, as well as their beneficial effects on fatigue strength, have been experimentally and numerically analyzed and quantified. The results of the experimental studies show that the benefit of high frequency peening methods relies on compressive residual stresses and surface hardening, caused by plastic deformation of the edge layers at the weld toes. The experimentally-determined fatigue strength of new welds and that of already fatigue-pre-loaded welds before the treatment is improved by 80 to 100 percent, as compared with the as-welded condition. Based on the findings, a design model for post-weld treated welds is developed, which allows for the consideration of the beneficial effect of the post-weld treatment for the design of steel structures. The increased fatigue strength is considered in a local design concept, by introducing improvement factors for the local fatigue strength. The local compressive stresses are considered, as well as the local stress ratio.