scholarly journals NUMERICAL METHODS FOR THE FATIGUE ASSESSMENT OF WELDED JOINTS: INFLUENCE OF MISALIGNMENT AND GEOMETRIC WELD IMPERFECTIONS

2017 ◽  
Vol 9 (1) ◽  
pp. 9-24 ◽  
Author(s):  
Andreas TARAS ◽  
Harald UNTERWEGER
Keyword(s):  
Numerical Methods ◽  
Welded Joints ◽  
Numerical Models ◽  
Hot Spot ◽  
Nominal Stress ◽  
Geometric Imperfections ◽  
Hot Spot Stress ◽  
Notch Stress ◽  
Effective Notch Stress ◽  
Nominal Stress Approach

The fatigue design life of welded joints in steel structures is increasingly assessed by using numerical models and methods, such as the structural (hot-spot) stress method and the effective notch stress method. When compared to the classical design approach using nominal stress S-N design curves, these methods offer the advantage of flexibility and a wider scope of application. However, a number of questions arise when these methods are used to assess geometrically "imperfect" welded joints, such as joints with plate misalignments or excessive weld convexity or concavity. In these cases, the classical S-N curves are known to cover imperfections up to the common tolerance classes for fatigue-prone welded joints (e.g. in accordance with ISO 5817 class B). For the numerical methods, differing and conflicting recommendations exist on how to account for the geometric imperfections in the welded joints, with little or no background to these recommendations available. In this paper, a study is presented in which two standard welded joints (butt welds between plates of equal and unequal thickness; T-joints with fillet welds) are analysed with the help of the structural (hot-spot) stress and the effective notch stress approach, considering various levels of geometric imperfection up to the tolerance limits, and the resulting fatigue life predictions are compared to test results from the literature and the nominal stress approach predictions. Since the nominal stress approach curves are based on reliable statistical data and desired survival probabilities for these known, standard cases, this methodology allows one to determine the correct application of the numerical methods to cases with geometric imperfections. This information may be used for a pertinent refinement of design recommendations for these methods, as well as for cases where these methods are applied to fitness-for-purpose assessments - e.g. because the nominal stress approach is not applicable.

scholarly journals Fatigue assessment of welded joints using multiaxial fatigue space theory with nominal stress approach

2020 ◽  
Author(s):  
Chun Lu ◽  
Jiliang Mo ◽  
Hongqin Liang
Keyword(s):  
Fatigue Damage ◽  
Welded Joints ◽  
Damage Assessment ◽  
Error Distribution ◽  
Multiaxial Fatigue ◽  
Nominal Stress ◽  
Damage Evaluation ◽  
Space Theory ◽  
Welding Defects ◽  
Nominal Stress Approach

Welded joints are widely employed in engineering field and they are always the starting points of fatigue damage. Because of the unfavorable material and geometry characters, as well as initial welding defects, the fatigue damage evaluation of welded joints is an important and troublesome issue for engineers. In this article, multiaxial fatigue space theory proposed by the first author for smooth specimens is extended for the fatigue damage assessment of welded joints, by adopting nominal stress approach. The fatigue test data with different materials, loading paths, and welded joints geometries are used to validate the capability of this theory. The result indicates a strong parallelization between predicted life and experimental life, with a favorable prediction error and beneficial error distribution. It can be concluded that multiaxial fatigue space theory is a useful method for fatigue damage assessment of welded joints with the help of nominal stress approach.

Assessment of Weld Fatigue by Effective Notch Stress Approach

2015 ◽  
Author(s):  
Majid Anvari ◽  
Øyvind Fagnastøl ◽  
Bernt J. Leira
Keyword(s):  
Linear Relation ◽  
Welded Joint ◽  
Hot Spot ◽  
Nominal Stress ◽  
Notch Stress ◽  
Nonlinear Relation ◽  
Effective Notch Stress ◽  
Weld Fatigue ◽  
Weld Root ◽  
Nominal Stress Approach

Applicability of different approaches, i.e. nominal stress-, structural hot spot- and effective notch stress approach, for fatigue assessment of welded structures has been discussed. The effective notch stress approach was validated for a cruciform fillet welded and fully penetration welded joint, according to DNV guideline [1]. The same fillet welded joint was further investigated for varying weld sizes. The results show that with changing weld size, there are considerable differences between calculated stresses, and specially calculated fatigue lives, when comparing with nominal stress approach. Further investigations revealed that there is a nonlinear relation between effective notch stress and weld sizes, while comparison of the notch stress and nominal stress approaches indicate that a linear relation is to be expected. Based on the established methodology for the cruciform joint, another joint, i.e. a knee plate located in a horizontal brace of a drilling vessel, was assessed for weld root fatigue. Based on the proposed equations and the linear relation found between the nominal- and the notch stress S-N curves, a weld size providing a longer fatigue life at the weld root, rather than that at the toe, was proposed.

scholarly journals Nominal Stress-Based Estimation of Fatigue Life of Welded Joints

2020 ◽  
pp. 39-44
Author(s):  
Karolina Głowacka ◽  
Tadeusz Łagoda
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints ◽  
Nominal Stress ◽  
International Institute ◽  
Linear Fracture Mechanics ◽  
Linear Fracture ◽  
Complex Linear ◽  
Structural Stresses

The paper presents methods for determining the fatigue life of welded joints with particular emphasis given to typical joints. In addition, the article presents various possible nominal stress-based ways enabling the calculation of stresses, including structural stresses and involving the most complex linear fracture mechanics. The paper also discusses recommendations by the International Institute of Welding related to the determination of the fatigue life of welded joints in flat elements exposed to tension-compression conditions. The work is focused on assessing the fatigue life of welded joints (selected types) in accordance with the guidelines specified in related recommendations issued by the International Institute of Welding and taking into consideration the analysis concerned with the safety of such structures.

scholarly journals Nominal stress based equal fatigue bearing capacity design of HSLA steel V-shaped butt-welded joints

2018 ◽  
Vol 221 ◽  
pp. 01009
Author(s):  
Wen Xue ◽  
Ping Wang ◽  
Zhibo Dong ◽  
Hongyuan Fang
Keyword(s):  
Bearing Capacity ◽  
Welded Joints ◽  
Design Method ◽  
Hsla Steel ◽  
Estimation Method ◽  
High Strength ◽  
Nominal Stress ◽  
Fatigue Load ◽  
Capacity Design ◽  
Fatigue Life Estimation

Based on nominal stress, this paper proposed a fatigue life estimation method of V-shaped butt welded joints. Then, the fatigue bearing capacity of the base metal under the same fatigue load was used as design goal of the V-shaped butt welded joints and an equal fatigue bearing capacity (EFBC) design method for V-shaped butt welds was thus formed. High strength low alloy steel Q690 was chosen as the experimental material to carry out the equal fatigue bearing capacity design.

scholarly journals Nominal Stress-Based Equal-Fatigue-Bearing-Capacity Design of under-matched HSLA Steel Butt-welded Joints

Metals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 880 ◽  
Author(s):  
Xue Wen ◽  
Ping Wang ◽  
Zhibo Dong ◽  
Yong Liu ◽  
Hongyuan Fang
Keyword(s):  
Bearing Capacity ◽  
Fatigue Limit ◽  
Base Metal ◽  
Welded Joints ◽  
Design Method ◽  
Hsla Steel ◽  
High Strength Steels ◽  
High Strength ◽  
Nominal Stress ◽  
Load Carrying

Under-matched welds could minimize the tendency of cold cracking and reduce the preheating operations when high strength steels are welded. However, its low load-carrying capacity might make the high strength parent metal meaningless. With the aim of improving the fatigue limit of under-matched butt-welded joints, this work establishes a nominal stress based fatigue design method for under-matched butt welds while considering its heterogeneous mechanical features. The fatigue life of the base metal is set to be the design goal for the under-matched butt-welded joints, which has scarce been tried before. An equal-fatigue-bearing capacity (EFBC) design method fit for the under-matched butt-welded joints is thus applied with the aims of equal fatigue limit of base metal. X-shaped butt-welded joint is selected to carry out experimental verification where HSLA steel Q550 as the base metal and ER70S-6 as the under-matched filler metal are used. The results show that the EFBC method proposed here is feasible. Note that the EFBC method is valid only in high cycle fatigue.

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