Fatigue Life Of Welded Joints Research Articles

Model reduction for fatigue life estimation of a welded joint driven by machine learning

In structural mechanics, the design of component assemblies is fundamental for ensuring structural integrity and durability. Fatigue, a common failure mode, particularly challenges the validation of welded joints' fatigue resistance. Various analytical and numerical methods estimate fatigue life but often involve costly processes requiring extensive parameter adjustments and software integration. This study applies machine learning (ML) for metamodeling of a complete finite element analysis and fatigue analysis workflow for estimating the fatigue life of welded joints, considering geometric characteristics, loading conditions, and weld classes. The comparison of the effect of learning database configuration for several regression estimators has led to a reduced model that provides design rules. Our findings demonstrate the significant potential of ML to streamline complex frameworks and accurately estimate the fatigue life of welded joints, advancing AI's application in mechanical engineering.

Effect of non-proportional stress states caused by varying phase shifts on the fatigue life of welded joints

In this paper, the effect of multiaxial non-proportional stress states on the fatigue life of welded joints is investigated. The non-proportional stress states are caused by various phase shifts between the normal and shear stresses. In total 45, welded tube-to-tube specimens are tested under multiaxial proportional and non-proportional loading. The increase in fatigue damage caused by non-proportional stresses, compared to proportional stresses, is quantified by penalty factors. A set of penalty factors are derived from the fatigue experiments for use with the governing multiaxial fatigue criteria by the International Institute of Welding (IIW) and Det Norske Veritas (DNV). The experimental results show that phase shifts decrease the fatigue life. However, this reduction is not to the extend proposed by the governing guidelines. Furthermore, the results indicate that different degrees of phase shift do not induce varying levels of fatigue life degradation.

EXPERIMENTAL STUDY ON MAG WELDED E350 HSLA STEEL JOINTS

Activated flux has been used successfully to improve the penetration of Tungsten Inert-Gas (TIG) welding, which is normally a welding process with low penetration. But the same activated flux when used for Metal Active Gas (MAG) welding showed a moderate improvement in penetration. Hence only a few research articles reported on activated flux MAG welding. TIG dressing is a post-weld treatment intended to improve the fatigue life of welded joints. The use of activated flux along with TIG dressing were not yet reported. In this work, an experimental study was conducted on the metallurgical changes and their effects on fatigue life in E350 steel welded by MAG welding with activated flux coating as well as toe TIG dressing. The metallurgical changes induced by various weld conditions and the effect on the fatigue life of welded joints were discussed. Welding conditions were categorised as: as weld (AW), weld with flux coating (FW), weld with TIG dressing (AWT), and flux weld with TIG dressing (FWT). Fatigue tests at stress ranges closer to the yield stress (80 % to 90 % of yield) were studied. In comparison with AW joints, the AWT and FWT showed a fatigue-life improvement of 60 % to 80 %, and 69 % to 103 % respectively. Whereas the FW joints showed 10 % to 17 % deterioration in fatigue life. Upon investigation with electron microscopy it was found that the variation in grain sizes and phase changes induced by the usage of flux and TIG dressing, as well as the changes in weld toe radius by TIG dressing and root strengthening due to extra penetration induced by the use of flux were the reasons behind these fatigue behaviours. In this work a novel effort is made to find a way to improve the fatigue life of a welded joint with a combination of two techniques. The activated flux is used to improve the penetration, whereas TIG dressing is performed to reduce the stress concentration. This new combination of techniques has improved the fatigue life of the weld significantly, which can lead to reduced maintenance costs of welded joints and a longer life.

Framework for a finite element method-based simulation approach to fatigue assessment of welded joints using the 4R method

The increased tensile strength capacity of high-strength steels (HSS) can be utilized fully in static loads, for fluctuating loads, however, more detailed analysis of design and manufacturing is needed. This study presents a framework for investigating utilization of the finite element method (FEM) in multiparametric 4R method-based fatigue evaluation. More specifically, the aim of the current study is to produce a concept for determining the parameters of the 4R method using FEM, thus providing a tool for evaluating fatigue strength related factors numerically. The study examines gas metal arc welded (GMAW) longitudinal gusset joints made of HSS S700MC Plus. The simulation is carried out as a sequentially coupled welding analysis that includes material condition changes in the HAZ and the fluctuating response as a restart analysis. Experimental measurement is performed for comparison with the results of the numerical model in the intermediate stages of the analysis process, and in the final stage as regards fatigue life. The experimental and simulated sub-results are consistent, and the estimated fatigue lives are in relatively good agreement with the experimental fatigue results. The numerical method thus provides a tool to predict fatigue related factors considered in 4R to evaluate fatigue life of welded joints.

Study on Fatigue Performance of Pulsed Tungsten Inert Gas Welding Joint of Duplex Stainless Steel Thin Tube.

To solve the shortage of austenite phase precipitation caused by nitrogen loss in the welding process of UNS S2205 duplex stainless steel (DSS), shielding gas nitriding was investigated by adding different N2 contents in Ar shielding gas during the welding process. A good thin-walled pipe butt joint was formed using the pulsed tungsten inert gas (P-TIG) welding method with Ar-N2 shielding gas. High cycle fatigue tests of the weld joints were conducted to study the effect of shielding gas nitriding on the fatigue properties. Fatigue tests at three stress levels of 225 MPa, 270 MPa, and 360 MPa were carried out on the weld joints with different N2 contents, and the fatigue samples were all fractured in the high temperature heat-affected zone (H-HAZ). Within the current process parameters, the fatigue life of the 4 vol.% N2 welded joints was optimal. Fatigue striations appeared in the fatigue crack propagation zone, and the transient fracture zone was similar to the tensile fracture. Under the low-stress level, the area of the crack propagation zone under 4 vol.% N2 was the highest, the tear ridges all expanded around the crack source area, and the fatigue crack propagation zone presented a radial distribution. The proliferation and expansion of dislocations were mainly carried out in the austenite grains, and the dislocation density of the fatigue specimens under 4 vol.% N2 was smaller than that of the Ar specimens. Shielding gas nitriding effectively improved the balance of the two-phase ratio and the hardness of austenite phase, optimized the internal slip system, inhibited the proliferation of dislocations in the austenite phase, and improved the fatigue life of weld joints.

Effect of the Filler Metal and Shielding Gas on the Fatigue Life in HSLA Steels Welded Using the GMAW Process

The composition of the filler electrodes, as well as the shielding gases, has a strong impact on the static and dynamic properties of welded joints in HSLA steels. The content of Cr, Ni, and Mo, along with the shielding gases, helps maintain the hardness values in the HAZ of HSLA steels welded using the GMAW process, resulting in a positive impact on the fatigue life of the joints. Maintaining fatigue properties in the regions of the heat-affected zone is crucial. The increase in the size of the HAZ, coupled with microstructural changes, leads to a reduction in the hardness values in this region, contributing to a decrease in the fatigue life of welded joints. In this study, the effects of using different filler electrodes and shielding gases on the fatigue properties of welded joints in LNE 600 steel with a thickness of 4.75 mm, welded using the GMAW process, were evaluated. It was possible to observe a reduction in the hardness values in the HAZ region and a similar static resistance behavior for all evaluated conditions, except for the ER70S-6 electrode with 5% O2 gas, where the fatigue life showed better results with the application of the ER120S-G electrode.

Fatigue assessment of welded joints and crack growth considering residual stress

There are different approaches to investigate the fatigue life of welded joints, however, less has been done considering residual stresses. The heat and residual stress distribution of a butt weld joint are determined using ABAQUS software and the results are validated against experimental and numerical studies in the literature. The software FE-SAFE is used to study the fatigue life of a GMAW welded butt joint under high cycle loading considering the residual stress. The corresponding S-N curve is determined, and the results show that the longer the length of welds, the higher residual stress and lower fatigue life. The crack nucleation and propagation in the butt weld simulated using XEFM software, and it is found that crack starts from the position of highest restrain.

Fatigue life analysis of welded joints in the frequency plane in a structure designed for the defense industry

Welded joints are used in many industrial products and evaluations against static and dynamic stresses are important in terms of structure and life safety. It is very difficult to predict and model the vibration fatigue life of welded joints in the frequency plane under dynamic stresses. In this study, fatigue life estimation was made in the welded joint on a structure under vibration stresses in the frequency plane. Vibration characteristics for modes up to 1000 Hz were determined by modal analysis of the structure. In the MIL-STD 810G standard, power spectral density (PSD) is offered for composite wheeled vehicles, which are products of the defense industry. Random vibration analyzes were performed by defining PSD data as analysis input. With the effective notch stress approach, geometry and material S-N definitions were made and evaluations were carried out according to the Dirlik method. As a result of this study, the fatigue life of welded joints was determined as 4.582e+11 seconds. Approaches for structural reliability in a welded joint structure designed for the defense industry are proposed.

Simultaneously increased strength and plasticity of TIG-welded 7075-T6 aluminum alloy joints via a novel post-weld composite treatment process

The 7075-T6 aluminum (Al) alloy is a high-strength material with great application potential. However, the tensile strength and elongation of its arc-welded joints are severely reduced compared to the base metal (BM), with only 57.3% and 14.4% of the BM values, respectively. To improve both strength and plasticity simultaneously, a novel post-weld composite treatment process combining solution treatment, partial rolling, and natural aging treatment (SRA) was proposed. The SRA process enhanced the strength and elongation of welded joints to 84.5% and 83.1% of the BM, respectively. In different regions of the joints, the SRA process involved different strengthening mechanisms, including stronger work hardening in Region I, η′ phase precipitation and weaker work hardening in Region II, and refinement of the η’ and η phase in Region III. The SRA process also improved the formability of the welded joints from 62.5% to 87.5% of the BM. In addition, the SRA process increased the median fatigue life of welded joints by a factor of approximately 2–6. This was achieved by increasing the strength and microhardness of the fusion zone, which, in turn, reduced the number of fatigue crack sources and shifted crack sources from the surface to subsurface regions.

Using 3D‐scanners and finite element method to assess the fatigue life of welded joints based on the actual geometry of seam welds: realistic modelling of notches at the weld toe

AbstractTo predict the service life of welded joints, the seam welds of samples (cross joint, K‐seam, sheet thickness 15 mm and a laser‐welded butt joint, sheet thickness 6 mm, both made of steel quality S 355) are recorded using a 3D scanner. The data obtained in this way is processed and transferred to a finite element method program. The meshing of the weld seams is very detailed. A finite‐element‐method stress calculation is then carried out. The real samples are tested in a fatigue test up to the point of cracking. The results from calculation and test are then compared. A possible crack location can be predicted very well using the finite element method results. The cracks in the real test are always in the area of very high or often the absolute highest calculated stresses. A prediction of the service life in the fatigue test is possible with a certain scatter – close to the usual scatter for welded joints. Based on the results of 19 samples, a fatigue class for local stress (based on the real geometry) of FAT 300 can be preliminary estimated for the cross‐joint specimens. Definition according to the specifications of the International Institute of Welding (FAT at 2 mio. cycles, survival probability 97.7 %).

Fatigue deformation mechanisms and dislocation model of 41Fe-25.5Ni-23.5Cr alloy welded joints under multistage heat treatment

The fatigue behavior of 41Fe-25.5Ni-23.5Cr alloy welded joints subjected to different multistage post-weld heat treatment (PWHT) conditions was studied. The fatigue life of welded joints under PWHT1 (600 °C-1 h/1050 °C-1 h/950 °C-30 min) was significantly prolonged, which was attributed to the low cyclic hardening rate caused by the small cyclic yielding stress and effective stress. The microstructure analysis indicated that the twin boundaries in the fusion line maintained continuity with those in the base metal, causing the inhomogeneous fatigue deformation to be primarily distributed in the weld metal rather than the fusion line. The crystallographic orientation (001) of weld metal under PWHT1 remained unchanged during fatigue, the slip of bowed dislocation lines was the characteristics of fatigue deformation and the grain growth led to the decrease in weld metal deformation. The crystallographic orientation under PWHT2 (1050 °C-1 h) changed from (111) to (001), and the slip of tangled dislocation lines resulted in an accumulation of weld metal deformation. To study the impact of deformation behavior on fatigue properties, new dislocation slip models were developed based on the increase in dislocation density caused by the parabolic slip area and dislocation line length. The results of this study indicate that multistage PWHT is a remarkable approach to prolong the fatigue life of 41Fe-25.5Ni-23.5Cr alloy welded joints at high temperatures.

Fatigue failure investigation of thick plate butt‐welded joints with incomplete penetration effect

AbstractThe objective of this paper was to investigate the fatigue performance of the thick plate structural steel butt‐welded joints influenced by its geometrical factors, such as the notch angles, incomplete penetration length, and plate thickness. Utilizing experimental tests, finite element calculations, and analytical models, the fatigue behavior of various weld joint shapes and dimensions was analyzed, and the discrepancy of fatigue strength for different incomplete penetration lengths was evaluated using the nominal stress method. Meanwhile, the local approaches, including notch stress intensity factor (NSIF), averaged strain energy density (SED), effective notch stress (ENS) method, peak stress method (PSM), and implicit gradient effective stress (IGES) method, are employed to assess the fatigue life of thick plate welded joints. According to the results, incomplete penetration ratios in butt‐welded joints led to a decrease in fatigue strength. The analytical solutions of butt‐welded joints in high cycle regime based on SED results were obtained to estimate the fatigue characteristic values for different plate thickness and incomplete penetration ratios. The proposed equations could illustrate the relationship between the nominal stress and local SED dealing with the variations of incomplete penetration length and geometrical dimensions. Moreover, the results obtained by the analysis of ENS, PSM, and IGES could be deduced by the analytical models to determine the fatigue life of welded joints.

Estimation of fatigue life of welded structures incorporating importance analysis of influence factors: A data-driven approach

The fatigue life prediction of welded joints with different specifications under different conditions was a challenging issue due to the quite complex influence. Specifically, the current fatigue life prediction methods lacked comprehensive analysis of multiple influence factors and reasonable incorporation of physical models. So, the analysis of factors influencing the fatigue life of welded joints and the fatigue life prediction were critical to the safety and reliability of engineering structures. In this study, a prediction approach for fatigue performance was proposed based on influence factor analysis using data-driven methods. The fatigue performance dataset was processed via physical models to realize the physics-based analysis of the factors affecting fatigue performance. The weights of the physics-informed influence factors on the fatigue life were analyzed using the extreme gradient boosting (XGBoost) algorithm and verified by cross-validation. The prediction results extracted from the SN curves predicted by the deep convolutional neural network (DCNN) model incorporating the weight analysis of influence factors exhibited better accuracy and stability than direct prediction and other existing prediction models. Because of the advantages of DCNN in avoiding over fitting and local optimization, the proposed approach can better describe and estimate the fatigue performance of welded structures.

Study on the influence of the shape and properties of Q345R welded joints on stress concentration and fatigue life

For the commonly used pressure vessel material Q345R, the theoretical formulas of stress concentration factor (SCF) and fatigue life of welded joints were derived. A finite element analysis model was established to systematically study the theoretical SCF and fatigue life of the joint. The results show that the theoretical SCF increases by 45% with the increase of reinforcement height and decreases by 9.9% with the increase of fillet radius. In addition, the weld width and wire material have no effect on SCF. The fatigue tests of three typical welded specimens were carried out. The experimental results were basically consistent with the finite element analysis results, which proved the reliability of the analysis model and provided theoretical guidance for the actual detection and evaluation.

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.