Fatigue Crack Growth Assessment of Welded Joints in Ships Structures: A Reliability-Based Sensitivity Study

2006 ◽  
Author(s):  
Cesare Mario Rizzo ◽  
Efren Ayala-Uraga
Keyword(s):  
Sensitivity Analysis ◽  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints ◽  
Sensitivity Study ◽  
Reliability Model ◽  
Structural Details ◽  
Before And After ◽  
Influencing Parameters ◽  
Growth Assessment

Fatigue life calculations have been recently introduced as explicit checks in classification societies rules for shipbuilding. Such checks are based on the classic S-N approach, which cannot be easily applied to the condition assessment of structural details. Fracture mechanics approach allows describing the structural degradation of ageing structures and the reliability framework accounts for the inherent probabilistic aspects of fatigue. This approach gains relevance as many ship tankers are being converted to operate as offshore ships. This paper carries out a sensitivity analysis of the reliability model for fatigue life calculations of typical ship’s welded joints based on fracture mechanics, aiming to select the most influencing parameters, before and after inspection updating.

Fatigue life assessment of welded structures based on fracture mechanics

2015 ◽  
Vol 6 (1) ◽  
pp. 2-25
Author(s):  
A. Krasovskyy ◽  
A. Virta
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints ◽  
Welding Process ◽  
Life Assessment ◽  
Lifetime Estimation ◽  
Worst Case ◽  
Welded Structures ◽  
Content Type ◽  
Fatigue Life Assessment

Purpose – Even though modern welding technology has improved, initial defects on weld notches cannot be avoided. Assuming the existence of crack-like flaws after the welding process, the stage of a fatigue crack nucleation becomes insignificant and the threshold for the initial crack propagation can be used as a criterion for very high cycle fatigue whereas crack growth analysis can be applied for the lifetime estimation at lower number of cycles. The purpose of this paper is to present a mechanism based approach for lifetime estimation of welded joints, subjected to a multiaxial non-proportional loading. Design/methodology/approach – The proposed method, which is based on the welding process simulation, thermophysical material modeling and fracture mechanics, considers the most important aspects for fatigue of welds. Applying worst-case assumptions, fatigue limits derived by the weight function method can be then used for the fatigue assessment of complex welded structures. Findings – An accurate mechanism based method for the fatigue life assessment of welded joints has been presented and validated. Originality/value – Compared to the fatigue limits provided by design codes, the proposed method offers more accurate lifetime estimation, a better understanding of interactions between welding process and fatigue behavior. It gives more possibilities to optimize the welding process specifically for the considered material, weld type and loading in order to achieve the full cost and weight optimization potential for industrial applications.

Determination of Some Parameters for Fatigue Life in Welded Joints Using Fracture Mechanics Method

2010 ◽  
Vol 19 (9) ◽  
pp. 1225-1234 ◽  
Author(s):  
A. M. Al-Mukhtar ◽  
H. Biermann ◽  
P. Hübner ◽  
S. Henkel
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints

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.

Uncertainties of Crack Propagation Analysis in Ship Structures

2016 ◽  
Author(s):  
Wengang Mao ◽  
Jingxia Yue ◽  
Da Wu ◽  
Luis De Gracia ◽  
Naoki Osawa
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Fatigue Cracks ◽  
Estimation Methods ◽  
Ship Structures ◽  
Residual Fatigue Life ◽  
Propagation Analysis ◽  
Structural Details ◽  
Residual Fatigue

Fatigue cracks can be observed quite frequently on today’s ocean crossing vessels. To ensure the safety of ship structures sailing in the sea, it is important to know the residual fatigue life of these damaged ship structures. In this case, the fracture mechanics theory is often employed to estimate how fast these cracks can propagate along ship structures. However, large uncertainties are always associated with the crack prediction and residual fatigue life analysis. In this study, two uncertainties sources will be investigated, i.e. the reliability of encountered wave environments connected with shipload determinations and different fracture estimation methods for crack propagation analysis. Firstly, different available codes based on fracture mechanic theory are used to compute the stress intensity factor related parameters for crack propagation analysis. The analysis is carried out for both 2D and 3D cases of some typical ship structural details. The comparison is presented to illustrate the uncertainties of crack propagation analysis related with different codes. Furthermore, it is assumed that the structural details will undertake dynamic loading from a containership operated in the North Atlantic. A statistical wave model is used to generate wave environments along recorded ship routes for different years. The uncertainties of crack growth analysis related with encountered weather environments is also investigated in the study. The comparison of these two uncertainties indicated the requirement of further development for the fracture mechanics theory and associated numerical codes, as well as the reliable life-cycle encountered weather environments.

Microstructure and Strain-Based Fatigue Life Approach for High-Performance Welds

2014 ◽  
Vol 891-892 ◽  
pp. 1500-1506 ◽  
Author(s):  
Heikki Remes ◽  
Pauli Lehto ◽  
Jani Romanoff
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Crack Growth ◽  
Welded Joints ◽  
Welded Joint ◽  
Damage Zone ◽  
Stress Gradient ◽  
Fatigue Crack Initiation ◽  
Initiation Period

Microstructure and pre-existing surface flaws in smooth notch geometries significantly affect the fatigue life of welded joints. Traditionally, a welded joint is assumed to incorporate crack-like defects and the crack propagation dominates the total fatigue life. For a smooth weld notch geometry, the macro crack initiation period becomes more significant, and this difference cannot be modelled with the existing stress or fracture mechanics ‑based approaches. In this paper, a microstructure and strain ‑based fatigue life approach is presented. In the approach, the fatigue damage process is modelled as a repeated crack initiation process within a material volume related to the microstructure. The novelty of the developed approach is that the size of the damage zone is defined from the grain size statistics without using fracture mechanics. The approach is able to consider the changes in the stress gradient, stress triaxiality and plasticity during the fatigue crack initiation and growth. The developed approach has been validated with experiments on submerged-arc and laser-hybrid welded joints. The predicted fatigue life, crack growth path and rate showed good agreement with the experiments. For a welded joint with smooth and favourable notch shape, the short crack growth, i.e. macro crack initiation period is dominant and it has a significant influence on the fatigue life.

Fatigue Life of Welded Joints of AISI 347 Stainless Steel Under Thermomechanical and Variable Amplitude Loading

2018 ◽  
Author(s):  
Alexander Bosch ◽  
Sophie Schackert ◽  
Michael Vormwald ◽  
Christoph Schweizer
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints ◽  
Power Plants ◽  
Crack Opening ◽  
Base Material ◽  
Damage Parameter ◽  
The One ◽  
Development And Validation ◽  
Flexible Operation

The change in operation of conventional power plants — due to the increasing use of renewable energies — from a stationary to a more flexible operation, causes additional stresses to the components by a high amount of smaller load cycles. This fact results in a demand for validated new concepts to estimate fatigue life especially for welded joints which are the weak parts within the piping. Resulting from the measured stains during operation in the LCF regime, a non-linear fracture mechanics based concept was chosen. For the development and validation of the model, different experiment types are carried out using various types of specimens. To consider the influence of different microstructures within a welded component, specimens made of X6CrNiNb18-10 (AISI 347) with the microstructure found in the base material on the one side, and as found in the HAZ on the other side are used. To take the influence of a mechanical and microstructural notch into account, notched specimens of X6CrNiNb18-10 (AISI 347), and welded specimens made of X6CrNiNb18-10 (AISI 347, base material) and X5CrNiNb19-9 (weld material) are used. Experiments are performed with all types of specimens with an increasing complexity from constant amplitude loading to operational loading. The developed nonlinear fracture mechanics based lifetime model uses the effective cyclic J-Integral normalized to the crack length to replace crack growth calculation by a linear damage accumulation. To consider the loading history an algorithm for the calculation of crack opening and crack closure is used. The advantages of this approach are shown by a comparison with damage calculations based on the damage parameter by Smith, Watson and Topper and based solely on the strain ranges. The differences in the concepts will be highlighted and used for further considerations of how to advance the lifetime prediction model for variable amplitudes. The presented work gives an overview of the preliminary results of the current work on the AiF research project 18842 N ‘Extended damage concepts for thermomechanical loading under variable amplitudes and plastic deformation’.

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