Fatigue Life Of Welded Joints Research Articles

Influence of Welding Residual Stress on Fatigue Life of Welded Joint Treated by Ultrasonic Peening

Influence of Welding Residual Stress on Fatigue Life of Welded Joint Treated by Ultrasonic Peening

A fracture mechanics-based stress approach for fatigue life prediction of welded joints considering weld profile effect

This paper presents a new method, based on fracture mechanics analysis of fatigue, to calculate the generalized stress proposed by Maddox. The generalized stress is computed from the currently existing structural stress definition and the stress intensity factor (SIF) calculation. With the structural stress term accounting for the effect of global weldment geometry, the stress intensity factor captures the local effect of the weld profile, characterized by the weld angle and weld toe radius. Weight function methods are used for the purpose of obtaining the generalized stress. Finally, the generalized stress is validated with fatigue test results of various specimen types and thickness combinations (up to 4.9 mm). It is found that the generalized stress is able to effectively predict the fatigue life of welded joints and can serve as a better fatigue damage parameter than the structural stress since the weld profile effect has been included.

An investigation on residual stress and fatigue life assessment of T-shape welded joints

This paper aims to quantitatively evaluate the residual stress and fatigue life of T-type welded joints with a multi-pass weld in different direction. The main research objectives of the experimental test were to test the residual stress by changing direction along with multiple wielding passes and determine the fatigue life of the welded joints. The result shows that compressive residual stress increases in the sample gradually from single-pass weld to double and triple-pass weld. Moreover, the fatigue life of the specimen also gradually improves with an increasing number of welding passes. Performing multi-pass welding in different directions affects the material’s residual stress and fatigue life, which is an essential factor to consider for assuring the strength of the welded joint.

Review of Fatigue Assessment Approaches for Welded Marine Joints and Structures

Welded joints are widely used in many sectors and represent the main joining technique also in the marine industry. The welded joints are sites of high stress concentrations and are subject to severe conditions for the marine environment. The design of marine welded joints has to consider the effects from wave loads, ship motions and loading/unloading operations and corrosion effects. The aim of this scientific work is to discuss about the state of the art of the standards and the approaches for predicting the fatigue life of welded joints used for the marine industry. Several approaches are examined in order to provide an overview and highlight the advantages and limitations of each method. Furthermore, recent advances in welding of dissimilar metals and autonomous welding are considered.

Influence of the mean stress on the fatigue life of welded joints under variable amplitude loading

The effect of the mean stress on the fatigue life of welded jointsfabricated with three different plate thicknesses was investigatedunder variable amplitude (VA)loading. Test results indicate thatMiner's sum, D, at failure increases as reducing the mean stress in the VA loading; hence, limiting D to 0.5, as advised in the fatigue design codes, may be unduly conservative in the fatigue assessment. The joint with a thinner plate is tend to have a better fatigue performance. New analytical models which can consider both mean stress and VA loading sequence effect were developed for better prediction of the fatigue life.Good agreement is observed between predictions and test results.

Intergranular corrosion effect on fatigue behavior of dissimilar 6005A‐5083 aluminum alloys weld joints

AbstractThe effects of the intergranular corrosion (IGC) defect depth on the high circle fatigue performance of tungsten inert gas (TIG)‐welded joints of 6005A–5083 dissimilar aluminum alloys were investigated. After soaking in different IGC solutions for 72 h, corrosion defects of different depths were generated in various areas of the specimen surfaces. It was found that the 5083 base metal exhibited the poorest corrosion resistance, while the welded metal displayed the best corrosion resistance. Fatigue tests carried out after precorrosion revealed that when the IGC depth was shallow, the weld defects on the weld metal were the main source of cracking for fatigue extension. However, when the IGC depth in the 5083 base metal was >248 μm, the corrosion defect acted as the origin of the fatigue crack, and the fatigue life of the sample was significantly reduced. This was attributed mainly to the local high‐stress field at the tip of the corrosion defect. Finally, a corrosion fatigue crack expansion model was established to analyze the influence of the corrosion defect depth on the fatigue lives of welded joints.

Sequence effect of as-welded and HFMI-treated transverse attachments under variable loading with linear spectrum

It has been shown in several studies that methods to improve the fatigue strength of welded structures, such as high-frequency impact treatment (HFMI), can increase the fatigue life of welded joints [1–6]. The results of these investigations led to current guidelines and recommendations for the fatigue assessment of HFMI-treated welded joints. Nevertheless, in practice, there are reservations regarding the efficiency of HFMI-treated welded steel joints under variable amplitude loading. Recent results [7] from studies on transverse attachments of the material S355 and S700 under variable amplitude loading show that the fatigue strength increasing effect of the HFMI-treatment is maintained compared to the as-welded state. The aim of this study is to analyse the sequence effect on the fatigue strength of HFMI-treated transverse attachments and to validate the applicability of linear damage accumulation hypotheses for the design of as-welded and HFMI-treated welded details. In this paper, fatigue test results with random variable amplitude loading (VAL) and high-low VAL and low–high VAL with linear spectrum for the two states as-welded (AW) and HFMI-treated joints will be presented.

Fatigue strength assessment of three-dimensional welded joints with the JV parameter

In this paper, the use of the J-integral (namely JV) is extended to three-dimensional sharp V-notches to evaluate the fatigue life of welded joints under complex loading. In order to simplify the procedure, JV is evaluated as a line integral on the free surface of the V-notch without defining a path contour inside the material. The length of the integration path depends on the critical characteristic length ρ* equal to one millimetre for welded joints made of steel. The JV is evaluated along the weld profile and the position of maximum JV is numerically calculated by means of the FE method. A relationship between the J integral and the JV is found in the case of mode III loadings. Finally, welded joints obtained with an RHS profile made of steel and subjected to tensile loading, bending and torque have been analysed.

Influence of residual stresses on the fatigue life of welded joints. Numerical simulation and experimental tests

Residual stresses constitute an inevitable consequence of the most ordinary manufacturing processes, leading to high and not easily foreseeable stress field within a component. Fatigue design codes typically address residual stresses by means of very conservative assumptions, which may results in poorly optimized designs and unexpected failures. Nowadays, the increasing motivation towards an optimized material application require a more reliable fatigue assessment of welded joints and residual stress evaluation. This study investigates the influence of residual stresses on the fatigue assessment of a S355JR structural steel pipe-to-plate welded joint subjected to fully-reversed torsional and bending loading. Influencing factors, such as geometric discontinuities and the material heterogeneous microstructure were considered through numerical modelling and microstructural analysis respectively. Firstly, an uncoupled thermal–structural finite element simulation was carried out to assess the complete residual stress field within the specimen generated by a gas metal arc welding process. Both thermal and structural simulations were developed to achieve an optimal trade-off between simulation time and results accuracy. Then, residual stresses were mapped and included as initial condition in numerical models intended for fatigue damage factors calculation. Fatigue analysis was conducted by means of the Fatemi–Socie critical plane factor and the hydrostatic stress as local damage parameters. Experimental results were then used to corroborate numerical models and verify their capability in assessing the fatigue endurance. Both the experimental data and the applied damage factors have shown an effect of residual stresses on the fatigue life of welded joints when torsional loading was applied. Data further agreed that no influence of residual stresses was detected in the case of bending loading.

Fatigue damage evaluation of welded joints in steel bridge based on meso-damage mechanics

Welding is a rapid and flexible connection that facilitates the use of a broad range of steel bridge. However, fatigue cracks initiating from various welded connection details are common problems in steel bridges. Therefore, it is vital to accurately evaluate the fatigue damage evolution and fatigue life of welded joints in steel bridge. In this study, a fatigue damage evolution model based on the meso-damage mechanics was proposed to evaluate the fatigue damage of welded joints in steel bridge. The number density of micro-cracks was adopted as the damage variable in the fatigue evolution model. Finite element modelling and user material subroutine (UMAT) in ABAQUS were combined to simulate fatigue damage evolution of welded joints in steel bridge. The fatigue damage evolution model was embedded in UMAT while the UMAT was coupled with the finite element model of the welded joints under cyclic loading. Then, the proposed model was validated by fatigue tests. The fatigue damage evolution model was also used to investigate the fatigue damage evolution process, and fatigue life prediction of the typical welded joints specimens in orthotropic steel decks (OSDs) of steel bridge. The results indicate that the fatigue strengths of nominal stress method were estimated to be 65.7 MPa for typical welded joints. The fatigue cracks mainly initiating at the weld toe and propagating along the weld toe line. The simulation results indicate that the fatigue damage evolution model provides superior ability in evaluating fatigue damage process and fatigue life of welded joints in steel bridge.

Opportunities and partial problems of HFMI implementation in design of welded structures of rail vehicles

This paper highlights the main impacts of HFMI (High Frequency Mechanical Impact) technology on increasing the fatigue resistance and extending the fatigue life of welded joints. In the case study there are SN curves of T-welded joints made of two different steels (conventional steel S235JR and high strength steel S460MC). For both materials there is a comparison of SN curves with and without HFMI treatment. Both samples are loaded by bending for cycle asymmetry R = 0. The failure criterion is a decrease in stiffness caused by the formation of a macrocrack. The results of fatigue testing are then applied in a parametric study, which assumes a random loading of a selected structural detail in a railway application. Opportunities and barriers of the implementation of HFMI in practice are mentioned and documented according to results of laboratory experiments, which take place in cooperation with the university research center and the manufacturer of railway vehicles.

Effects of weld geometry and HAZ property on low-cycle fatigue behavior of welded joint

A previous experimental study by the authors clearly indicated that, due to the delay of the crack initiation, the butt-welded joint with smoother weld toe profile and harder weld metal had a longer low-cycle fatigue life. In the present study, supplementary numerical studies considering weld geometries and inhomogeneous mechanical properties are executed. Monotonic tensile and strain-controlled low-cycle fatigue tests on the reheated round bars are firstly conducted to characterize the mechanical properties for different zones of the butt-welded joints. The test results are used to calibrate the material constitutive model, which is then embedded into three-dimensional finite element models to investigate the low-cycle fatigue behavior of the butt-welded joints. The numerical results suggest the necessity of considering the effects of inhomogeneous material properties when evaluating the low-cycle fatigue of welded joints. It is also confirmed that decreasing weld toe stress concentration and simultaneously increasing weld metal strength can maximally increase the low-cycle fatigue life of welded joints compared to the individual changes for either one. These findings are expected to provide some insights into the low-cycle fatigue life improvement of welded joints.

Fatigue Life Assessment of Welded Joints by Combined Measurements Using DIC and XRD.

The existing methods of assessing the fatigue life of welded joints fail to consider local strain ranges and mean stress at the weld toe. The present work proposes a novel approach to assessing the fatigue life of welded joints by conducting measurements with digital image correlation (DIC) and X-ray diffraction (XRD) in combination. Local strain ranges at the weld toe of gusset welded joints were measured by DIC. Hammer peening was conducted on the welded joints to introduce different initial stresses. The influence of mean stress was investigated by considering initial residual stress measured by XRD and a perfect plastic material model. The fatigue experiment was carried out on specimens with and without hammer peening. The results showed that hammer peening could offset adverse welding deformation effectively, and introduce significant residual compressive stress. The fatigue failure life increased by more than 15 times due to hammer peening. The fatigue initiation life assessed by the proposed method was close to that based on nominal stress, indicating that the proposed method is reliable for predicting the fatigue initiation life of welded joints.

Is 2D numerical modelling of welding process able to capture the residual notch stress intensity factor values?

Because of its local nature, the influence of residual stresses on fatigue life of welded joints in the high cycle regime can be quantified by the residual notch stress intensity factor (R-NSIF). The standard methodology used for its assessment requires a very fine mesh and this is the reason why 2D numerical models were used first in literature. The calculation of R-NSIF values via 3D models is very recent. It was found possible thanks to rapid numerical techiques such as the peak stress method. This approach was proven to work well but R-NSIF values coming from 3D models were not consistent with those obtained through 2D models. This work is aimed at solving that apparent discrepancy. 2D and 3D welding process numerical simulations applied to a carbon steel were carried out taking into account effects of metallurgical transformations and by varying the main geometrical parameters of the plates. It was found that 2D models are able to capture the R-NSIF value that is observed in the stationary residual stress distribution of the corresponding 3D models.

A Novel Probabilistic Fatigue Life Prediction Method for Welded Structures Based on gPC

The traditional fatigue life prediction methods based on the S-N curve all believe that the parameters in the model are deterministic constants and can be categorized to the deterministic life prediction. However, in practice, it is difficult to carry out a large number of experiments due to the limitation of time or the possible shortage of funds. In addition, the specimens used in the experiments are not exactly the same, and the test operations and data reading depend on the accuracy of the test equipment as well as the subjective judgment of the testers, which result to the uncertainty of the S-N curve. Therefore, the uncertainty should be considered in order to improve the accuracy of the fatigue life prediction. In this paper, the uncertain factors affecting the fatigue life of welded joints are summarized, and the generalized polynomial chaos (gPC) is introduced into fatigue life prediction. A novel probabilistic fatigue life prediction method combined with the nonlinear cumulative damage model considering the uncertainty of the S-N curve is constructed. An illustrative example is presented to demonstrate the advantages of the proposed approach.

Does metallurgy affect the residual notch stress intensity factor value induced by welding operations? A comprehensive study via a 3D numerical model

The residual notch stress intensity factor (R-NSIF) was found useful to quantify the influence of residual stresses on fatigue life of welded joints. Its distribution along the weld bead was recently assessed by using a 3D model. Those works focused only on the calibration of the model rather than an analysis of the R-NSIF values as a function of alloy metallurgy. This work wants to fill that gap. Both a carbon steel and an aluminum alloy were considered. Phase transformations are found to significantly influence the R-NSIF distribution with values that are more accurate compared to those obtained via previous models.

Assessment the Partial Welding Influences on Fatigue Life of S700MC Steel Fillet Welds

Fine-grained steels belonging to the HSLA group (High-Strength Low-Alloy steels) of steels are becoming increasingly popular and are used in both statically and dynamically stressed structures. Due to the method of their production, and thus also the method use to obtain the required mechanical properties, it is really necessary to limit the heat input values for these steels during welding. When applying temperature cycles, HSLA steels in highly heated heat-affected zones (HAZ) reveal intensive grain coarsening and also softening behaviour. This subsequently results in changes in both mechanical and brittle-fracture properties, and the fatigue life of welded joints. While grain coarsening and structure softening have a major effect on the change of strength properties and KCV (Charpy V-notch impact toughness) values of statically stressed welded joints, the effect of these changes on the fatigue life of cyclically stressed welded joints has not yet been quantified. The paper is therefore conceived so as to make it possible to assess and determine the percentage impact of individual aspects of the welding process on changes in their fatigue life. To be more specific, the partial effects of angular deformation, changes that occur in the HAZ of weld, and the notch effect due to weld geometry are assessed.

Effect of Water Environment on Fatigue Behavior in X80 High Strength Steel CO2 Arc Welding Welded Joint

Fatigue life tests and fatigue crack growth rate (FCGR) tests in the air and water environment were conducted on X80 pipeline steel welded joints (welded by CO2 arc welding). Scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) were utilized to investigate the internal influential mechanisms of the water environment during fatigue crack initiation and propagation stages, respectively. Results show that a great many oxide particles induced by the water environment gradually formed the fatigue crack initiation site and decreased fatigue life of welded joints. Meanwhile, the preferred grain orientation of <001>//ND and CSL boundaries of Σ3, Σ11, Σ13c, Σ17b, Σ25a, and Σ25b are both prone to fatigue propagation when loading in the water environment. In addition, a coalescence of the stress intensity factor (SIF) range and water environment accelerated FCGR by motivating secondary slip systems of {112}<111> and {123}<111> in bcc crystalline structures.

新低変態温度溶接材料と全姿勢伸長ビード補修法による溶接接手の高疲労寿命化 -第2報：全姿勢伸長ビード補修法による角回し溶接継手の疲労寿命延伸-

新低変態温度溶接材料と全姿勢伸長ビード補修法による溶接接手の高疲労寿命化 -第2報：全姿勢伸長ビード補修法による角回し溶接継手の疲労寿命延伸-

Paper Review of “Effect of heat affected zone microstructure behavior under cyclic loading on fatigue life of weld joint”

Paper Review of “Effect of heat affected zone microstructure behavior under cyclic loading on fatigue life of weld joint”