Abstract
The majority of fatigue tests of welded specimens is based on shop-made samples generally exhibiting minor misalignment. Due to the challenge of ensuring misalignment-free joints in industrial manufacturing processes, investigations focussing on the effect of misalignment on the fatigue strength are important. Therefore, this paper deals with the influence of axial misalignment on the fatigue resistance of butt-welded ultra high-strength steel specimen. In addition, the effect of high frequency mechanical impact treatment (HFMI) on the fatigue performance is researched. In the course of the experimental investigations, specimens exhibiting three different levels of axial misalignment are manufactured. Fatigue tests at a stress ratio of R = 0.1 in as-welded condition reveal a significant drop in fatigue strength with increasing axial misalignment. Fatigue assessments of the as-welded test results based on nominal, structural and effective notch stress approach are performed taking into account the sample-dependent misalignment factor. The given equations enable an improved consideration of axial misalignment regarding to fatigue strength. The HFMI treatment increases the fatigue strength compared with the as-welded state; the detrimental effect of misalignment is less pronounced. A comparison to the current IIW guideline for HFMI treatment reveals a conservative assessment if IIW-recommended FAT values for as-welded condition are applied.
Highlights
Within industrial manufacturing processes, weld seams usually exhibit a certain amount of angular and axial misalignment affecting the fatigue strength of welded structures in service
The aim of this work is to investigate the effect of axial misalignment for ultra high-strength steel butt joints on the fatigue performance
Based on the results shown in this table, high frequency mechanical impact treatment (HFMI) treatment shifts the welding distortion in negative direction and increases its standard deviation
Summary
Weld seams usually exhibit a certain amount of angular and axial misalignment affecting the fatigue strength of welded structures in service. The majority of welded specimens utilised for gathering fatigue test data is manufactured in workshop resulting in minor axial misalignment and angular distortion for every tested specimen. In many cases, the effect of misalignment on the fatigue strength of the weld detail is not well covered by experiment. This may be critical for applying such values without additional misalignment factors for fatigue assessment. A thorough investigation focussing on the detailed effects of weld location in the plate, its length over width ratio and load magnitude by the use of analytical approaches is published in [3]. Further studies incorporating finite element simulation runs focus on more complex assemblies such as panel structures in ships or girth welds for pipelines [4, 5]
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