S-N Lines for Welded Thin Joints — Suggested Slopes and FAT Values for Applying the Notch Stress Concept with Various Reference Radii

An assessment of thin welded structures with actual IIW design lines results in an overestimation of fatigue lives (strengths) at high load levels and a conservative estimation at low load levels, in many cases, independently of the applied fatigue assessment approach (nominal, structural or notch stress). This is mainly due to the slopes of the design S-N line k = 3.0 for normal and k = 5.0 for shear stresses, which are valid for thick and stiff structures. To overcome this inconsistency for welded thin and flexible structures, the slopes k = 5.0 for normal and k = 7.0 for shear stresses are suggested, keeping the already known FAT values derived for the notch stress concept variants with rref = 1.0, 0.3 or 0.05 mm, respectively. However, the slope is not only determined by plate thickness; it is the result of an interaction between thickness, local geometry (stress concentration), structural stiffness, loading mode and last but not least residual stresses. This complexity makes it difficult to identify the driving parameters and to predict the slope of the S-N line in many cases.

[1]  Federico M. Mazzolani,et al.  En1999 Eurocode 9 : Design of aluminium structures , 2001 .

[2]  Cetin Morris Sonsino,et al.  Fatigue assessment of welded joints by local approaches : Fatigue assessment of welded joints by local approaches , 2006 .

[3]  Cetin Morris Sonsino,et al.  Fatigue assessment of welded joints by local approaches Second edition , 2007 .

[4]  C. M. Sonsino.  Light‐weight design chances using high‐strength steels , 2007 .

[5]  Cetin Morris Sonsino,et al.  Fatigue design of aluminium welded joints by the local stress concept with the fictitious notch radius of rf=1 mm , 2006 .

[6]  Jaime Buitrago,et al.  Fatigue Design and Performance Verification of Deepwater Risers , 2003 .

[7]  Cetin Morris Sonsino,et al.  Structural Durability Proof of Automotive Aluminium Safety Components - Present State of the Art , 2005 .

[8]  C. Sonsino.  Course of SN-curves especially in the high-cycle fatigue regime with regard to component design and safety , 2007 .

[9]  M. Fermér,et al.  Industrial experiences of FE-based fatigue life predictions of welded automotive structures , 2001 .

[10]  Cetin Morris Sonsino,et al.  Effect of residual stresses on the fatigue behaviour of welded joints depending on loading conditions and weld geometry , 2009 .

[11]  Cetin Morris Sonsino,et al.  Verification of FAT Values for the Application of the Notch Stress Concept with the Reference Radii Rref = 1.00 and 0.05 mm , 2010 .

[12]  Cetin Morris Sonsino,et al.  Assessment of the fatigue behaviour of welded aluminium joints under multiaxial spectrum loading by a critical plane approach , 2006 .

[13]  S. J. Maddox,et al.  Fatigue strength of welded structures , 1991 .

[14]  Cetin Morris Sonsino,et al.  High‐Strength Steels in Welded State for Light‐Weight Constructions under High and Variable Stress Peaks , 2008 .

[15]  Cetin Morris Sonsino,et al.  A Consideration of Allowable Equivalent Stresses for Fatigue Design of Welded Joints According to the Notch Stress Concept with the Reference Radii rref = 1.00 and 0.05 mm , 2009 .

[16]  Cetin Morris Sonsino,et al.  Fatigue strength of laser beam welded thin steel structures under multiaxial loading , 2006 .

[17]  Cetin Morris Sonsino,et al.  Fatigue assessment of laser welded thin sheet aluminium , 2003 .

[18]  C. M. Sonsino,et al.  fatigue assessment of welded joints in AlMg 4.5Mn aluminium alloy (AA 5083) by local approaches , 1999 .

[19]  A W Beeby,et al.  CONCISE EUROCODE FOR THE DESIGN OF CONCRETE BUILDINGS. BASED ON BSI PUBLICATION DD ENV 1992-1-1: 1992. EUROCODE 2: DESIGN OF CONCRETE STRUCTURES. PART 1: GENERAL RULES AND RULES FOR BUILDINGS , 1993 .

[20]  E. Gaylord,et al.  Design of Steel Structures , 1972 .