Considering size effects in the notch stress concept for fatigue assessment of welded joints

2012 ◽  
Vol 64 ◽  
pp. 71-78 ◽  
Author(s):  
Matthias Kaffenberger ◽  
Michael Vormwald
Author(s):  
Jürgen Rudolph ◽  
Ralf Trieglaff ◽  
René Stößlein ◽  
Fabian Hauser

The fatigue assessment of welded joints in different engineering disciplines is usually based on nominal, structural or notch stresses on one hand (elastic concept using component fatigue curves of load controlled test data) and local strains on the other hand (elasto-plastic concept using material fatigue curves of strain-controlled push-pull test data of un-notched and polished standard specimens). The concepts of the first mentioned group are implemented in widespread standards and recommendations such as [1] to [3]. The fatigue assessment procedure of the European standard for unfired pressure vessels (EN 13445-3, Clause 17 & 18 and related annexes) [4] is currently under revision with one focus on the elaboration of user friendly fatigue assessment options for welded components [5]. The current state of the art focuses on the application of an adapted structural hot spot stress approach to the fatigue assessment of welded pressure equipment [5]. Although this is a significant step forward, the implementation of a notch stress approach can furtherly increase the fatigue assessment options by detailed weld seam analysis. The paper focuses on respective methodological proposals and application examples of typical welded joints. The finite element analysis as part of the procedure has to be harmonized with the requirements of the assessment procedure. Of course, the compatibility of the hot spot stress approach and a notch stress approach has to be guaranteed for individual examples. The direct comparison of the different approaches allows for a qualitative evaluation of methods. The application of an appropriate master fatigue curve FAT100 and the limitations with regard of stress/strain ranges in the low cycle fatigue (LCF) regime as well as the fatigue assessment of welded joints with mild weld toe notches is the subject of special considerations. The latest recommendations of German Welding Society (DVS) [6] constitute a reference for the last two subjects raised.


2012 ◽  
Vol 34 (1) ◽  
pp. 2-16 ◽  
Author(s):  
C.M. Sonsino ◽  
W. Fricke ◽  
F. de Bruyne ◽  
A. Hoppe ◽  
A. Ahmadi ◽  
...  

Author(s):  
Dong Jin Oh ◽  
Jae Myung Lee ◽  
Myung Hyun Kim

The aim of this paper is to investigate the fatigue strength of the Invar alloy weld joints. Invar alloy is commonly used in cryogenic applications where a high degree of dimensional stability is required under temperatures. It is widely used in primary and secondary barriers of membrane-type liquified natural gas (LNG) containment system. The fatigue assessment of Invar alloy weld joints is evaluated based on the nominal stress, structural stress approach and effective notch stress approaches. A series of fatigue tests were carried out for two different types of welded joints with raised edge specimens and overlap joint specimens at room and cryogenic temperatures. The evaluation of the results exhibit that the local stress concept using the reference notch radius of r = 0.05 mm can be applied to the fatigue design of Invar alloy weld joints for plates with thicknesses less than 5 mm. The results are also compared with the available published data. Finite Element Analysis (FEA) is carried out to investigate FAT value and slope of the design curve for Invar alloy weld joints. The suggested fatigue design curves based on the effective notch stress concept indicate a lower FAT value compared to steel weld joints by IIW recommendations.


Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1249
Author(s):  
Yixun Wang ◽  
Yuxiao Luo ◽  
Yuki Kotani ◽  
Seiichiro Tsutsumi

The existing S-N curves by effective notch stress to assess the fatigue life of gusset welded joints can result in reduced accuracy due to the oversimplification of bead geometries. The present work proposes the parametric formulae of stress concentration factor (SCF) for as-welded gusset joints based on the spline model, by which the effective notch stress can be accurately calculated for fatigue resistance assessment. The spline model is also modified to make it applicable to the additional weld. The fatigue resistance of as-welded and additional-welded specimens is assessed considering the geometric effects and weld profiles. The results show that the error of SCFs by the proposed formulae is proven to be smaller than 5%. The additional weld can increase the fatigue life by as great as 9.4 times, mainly because the increasing weld toe radius and weld leg length lead to the smaller SCF. The proposed series of S-N curves, considering different SCFs, can be used to assess the welded joints with various geometric parameters and weld profiles.


2021 ◽  
Vol 144 ◽  
pp. 106076
Author(s):  
Hamidreza Rohani Raftar ◽  
Mohammad Dabiri ◽  
Antti Ahola ◽  
Timo Björk

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