Fatigue assessment of welded joints under variable amplitude loading using a novel notch stress approach

2017 ◽  
Vol 101 ◽  
pp. 177-191 ◽  
Author(s):  
T. Nykänen ◽  
H. Mettänen ◽  
T. Björk ◽  
A. Ahola
Keyword(s):  
Welded Joints ◽  
Variable Amplitude Loading ◽  
Fatigue Assessment ◽  
Variable Amplitude ◽  
Notch Stress

Fatigue assessment of metallic components under uniaxial and multiaxial variable amplitude loading

2018 ◽  
Vol 41 (6) ◽  
pp. 1306-1317 ◽  
Author(s):  
A. Carpinteri ◽  
S. Vantadori ◽  
T. Łagoda ◽  
A. Karolczuk ◽  
M. Kurek ◽  
...  
Keyword(s):  
Variable Amplitude Loading ◽  
Fatigue Assessment ◽  
Variable Amplitude

scholarly journals Integral treatment of butt joints for the fatigue life assessment in the low cycle fatigue regime

2020 ◽  
Author(s):  
Benjamin Möller
Keyword(s):  
Fatigue Life ◽  
Life Assessment ◽  
Cyclic Behavior ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Butt Joints ◽  
Variable Amplitude Loading ◽  
Fatigue Assessment ◽  
Variable Amplitude ◽  
Integral Treatment

Abstract The framework for a fatigue assessment of welded joints under service loading conditions of crane structures from the low cycle to the high cycle fatigue regime includes the consideration of elastic-plastic material behavior, variable amplitude loading, and acceptable calculation times. Therefore, an integral treatment of butt joints has been developed for fatigue life estimation. The butt weld is considered in its entirety, so that it can be described by its cyclic behavior. The evaluation of the cyclic stress-strain behavior and tri-linear strain-life curves of butt joints for different high-strength, fine-grained structural steels, derived by strain-controlled fatigue tests, is the basis for this description. This procedure is not limited to conventionally applied gas metal arc welding only, but also the fatigue assessment of laser beam welding is possible, for example. Cyclic transient effects have been analyzed and a distinctive cyclic softening is described by linearization of Ramberg-Osgood parameters, depending on the damage content of each cycle derived from constant amplitude, strain-controlled tests. On the basis of the cyclic behavior in combination with memory and Masing behavior, a simulation of the stress-strain paths of investigated butt welds, under constant and variable amplitude loading, has been performed. Damage parameters are used to accumulate the damage cycle by cycle in order to derive the fatigue lifetime. Finally, calculated fatigue lives were compared with experimentally determined lives, showing the impact of this procedure.

Qualification of the Notch Stress Approach for the Fatigue Assessment of Welded Pressure Equipment and Power Plant Components

2017 ◽  
Author(s):  
Jürgen Rudolph ◽  
Ralf Trieglaff ◽  
René Stößlein ◽  
Fabian Hauser
Keyword(s):  
Test Data ◽  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Hot Spot ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Element Analysis ◽  
Hot Spot Stress ◽  
Fatigue Assessment ◽  
Notch Stress

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.

Fatigue Life Prediction of Welded Joints for Offshore Structures Under Variable Amplitude Loading

1993 ◽  
Vol 115 (2) ◽  
pp. 123-130 ◽  
Author(s):  
R. Bell ◽  
O. Vosikovsky
Keyword(s):  
Fatigue Life ◽  
Welded Joints ◽  
Life Prediction ◽  
Experimental Tests ◽  
Offshore Structures ◽  
Multiple Cracks ◽  
Stress Range ◽  
Variable Amplitude Loading ◽  
Model Calculations ◽  
Variable Amplitude

This paper describes the development of a fracture mechanics model for the prediction of fatigue life of welded joints subjected to variable amplitude loading. The prediction program is based on the integration of the Paris equation. A novel feature of this program are relationships which account for the development, growth and coalescence of multiple cracks that occur at the weld toe. These relationships or forcing functions were developed from extensive monitoring of the initiation and crack shape development of multiple cracks during experimental tests. Data is also presented on a series of variable amplitude tests performed on welded T-plate joints loaded in 3-point bending using the common load sequence (COLOS) at a stress ratio of R=−1. These results are presented in terms of effective and root mean square stress ranges. The experimental data are used to validate the life prediction results from the growth model. A discussion is also included on the proportion of the compressive stress range to be included as an effective stress range in the prediction model calculations.

scholarly journals Sequence effect of p(1/3) spectrum loading on service fatigue strength of as-welded and high-frequency mechanical impact (HFMI)-treated transverse stiffeners of mild steel

2021 ◽  
Author(s):  
R. Schiller ◽  
D. Löschner ◽  
P. Diekhoff ◽  
I. Engelhardt ◽  
Th. Nitschke-Pagel ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Mild Steel ◽  
Welded Joints ◽  
High Frequency ◽  
Base Material ◽  
Experimental Results ◽  
Sequence Effect ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Mechanical Impact

AbstractIn the meantime, it’s well known that post-weld fatigue strength improvement techniques for welded structures like high-frequency mechanical impact (HFMI) treatment increase the fatigue live of welded joints. Although the current design recommendations for HFMI-treated welded joints give first design proposals for the HFMI-treated welds, in practice the application of HFMI treatment and the associated increase in fatigue resistance are still being discussed. There are, for example, reservations regarding the efficiency of HFMI-treated welded joints under variable amplitude loading (VAL). This paper analyses first results for the sequence effect of VAL of a p (1/3) spectrum on the service fatigue strength of HFMI-treated transverse stiffeners (TS) of mild steel (S355). Fatigue test results with random and high-low loading for the two states as-welded (AW) and HFMI-treated joints will be presented. The modified linear damage accumulation and the failure locations will be discussed. The experimental results show a clear change in the slope of the S-N curve from the as-welded (AW) state to the HFMI state and additionally in the HFMI state from constant amplitude loading (CAL) to variable amplitude loading (VAL). It was particularly noticeable in the experimental results of all tested HFMI series that the specimens failed exclusively in the base material 2–4mm before the HFMI-treated welds. The presented results of the investigations show that with application of the nominal stress concept, no sequence effect was recognizable.

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