Welded Structures Research Articles

Methods for Non-destructive Testing of Welding Residual Stresses in Aluminum Alloys

There will be large residual stress after welding, and the residual stress will affect the service life of the aluminum alloy welding structure. Therefore, aluminum alloy welding residual stress needs to be accurately detected. Compared with the lossy method, the nondestructive testing method can produce negligible damage to aluminum alloy, which will not affect the reuse of aluminum alloy and can detect the residual stress. This paper summarizes the nondestructive testing methods of welding residual stress in aluminum alloy and their advantages, disadvantages, and applicability, which lay a foundation for rapid nondestructive testing of welding residual stress in aluminum alloy.

Experimental and Numerical Predictions of Cryogenic Leakages in Welded Steel Plates

This study presented experimental and numerical research to investigate the effect of cryogenic leakage on a plate structure of AH36-grade steel containing welded joints. To simulate the cryogenic leakage conditions, the welded plate was exposed to a temperature of −196 °C by supplying liquid nitrogen (LN2) to the center of the steel plate. The time-dependent temperature history and strain variation were measured by using thermocouples and strain gauges attached to the plate surface. Additionally, the residual stress of the middle surface section before and after the cryogenic leakage process was measured by X-ray diffraction analysis (XRD). A three-dimensional finite element model was created with the use of a commercial finite element analysis (FEA) program to simulate the flux-cored arc welding process and cryogenic leakage process. The steel surface temperature dropped sharply and reached approximately −196 °C at 160 s after LN2 supplement. After the first 650 s of the LN2 leakage experiment, the outside of the trough reached approximately −75 °C and −25 °C, depending on the location of the thermal couples. Although there was a relative difference in the results, the experiment and numerical simulation results for temperature and stress distribution showed good agreement. The results could be utilized in the ship design stage adopting welded structures as a basic database.

Effect of tool tilt angle on microstructure, mechanical properties and fracture behavior of dissimilar friction stir lap welding joint of SiCp/ZL101 and ZL101

In order to achieve the lightweight goal of urban rail train braking system, friction stir lap welding (FSLW) was used to weld SiCp/ZL101 and ZL101 sheets to prepare a new type of brake disc material. The effects of different tool tilt angles (TTAs) on microstructure and mechanical properties of the welding joints were systematically studied. The TTA had a significant effect on the microstructure and defect formation of the dissimilar FSLW joints. There were tunnel defects under the advancing side at 1° and 2°. Internal defect-free weld structures were formed at 3° and 3.5°. A large number of dislocations caused by plastic deformation remained in the microstructure of the weld region at 1° and 2°, and the transformation of the microstructure of the weld region at 3° and 3.5° was dominated by dynamic recovery and dynamic recrystallization. The distribution of SiC particles in the nugget area was uniform, and the grains were obviously refined. With the increase of the TTA, the average grain size of the nugget area increased, the average size of the SiC particles decreased, and the average hardness of the nugget area increased. The four samples all formed a transition zone with good metallurgical bonding at the welding interface. The shear strength of the welding joints increased first and then decreased with the increase of the TTA. In the absence of welding defects, the shear strength reached the best level of 130.71 MPa at 3°. Both shear and tensile fractures were ductile fractures.

Microstructural Evolution and Mechanical Performance of Two Joints of Medium-Mn Stainless Steel with Low- and High-Alloyed Steels

In this work, 2 mm thick medium-Mn austenitic stainless steel (MMn-SS) plates were joined with austenitic NiCr stainless steel (NiCr-SS) and low-carbon steel (LCS) using the gas tungsten arc welding technique. A precise adjustment of the welding process parameters was conducted to achieve high-quality dissimilar joints of MMn-SS with NiCr-SS and LCS. The microstructural evolution was studied using laser scanning confocal and electron microscopes. Secondary electron imaging and electron backscatter diffraction (EBSD) techniques were intensively employed to analyze the fine features of the weld structures. The mechanical properties of the joints were evaluated by uniaxial tensile tests and micro-indentation hardness (HIT). The microstructure of the fusion zone (FZ) in the MMn-SS joints exhibited an austenitic matrix with a small fraction of δ-ferrite, ~6%. The tensile strength (TS) of the MMn-SS/NiCr-SS joint is significantly higher than that of the MMn-SS/LCS joint. For instance, the TSs of MMn-SS joints with NiCr-SS and LCS are 610 and 340 MPa, respectively. The tensile properties of MMn-SS/LCS joints are similar to those of BM LCS, since the deformation behavior and shape of the tensile flow curve for that joint are comparable with the flow curve of LCS. The HIT measurements show that the MMn-SS/NiCr-SS joint is significantly stronger than the MMn-SS/LCS joint since the HIT values are 2.18 and 1.85 GPa, respectively.

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.

Implementation of the Peak Stress Method for the automated FEA-assisted design of aluminium welded joints subjected to constant amplitude multiaxial fatigue loads

The Peak Stress Method (PSM) is a FE-oriented local approach to the fatigue strength assessment of welded structures subjected to fatigue loading. Starting from the peak stresses calculated at the V-notch tip nodes defining weld toes or the weld roots, the PSM defines an equivalent peak stress which allows to estimate the fatigue failure location and fatigue lifetime of welded structures, in compliance with appropriate fatigue design curves. An Ansys® Mechanical extension has been developed to achieve full automated implementation of the tasks and calculations necessary to apply the PSM to welded structures. The tool allows to identify and analyse all the V-notch tip edges of the structure and perform fatigue life estimation on each analysed node. As an output, fatigue life results can be visualized through dedicated tabular data, graphs and contour results generated over the edges of the model. In this work, common-to-complex 3D geometries taken from the literature and related to aluminium alloys welded joints subjected to uniaxial as well as multiaxial fatigue loads have been analysed by comparing two design approaches: (i) manual application of the PSM, (ii) automated implementation of the PSM. The tool developed in Ansys® Mechanical allows to significantly contain the time and effort required to analyse welded structures according to the PSM.

Verification of the Maximum Stresses in Enhanced Welded Details via High-Frequency Mechanical Impact in Road Bridges

High-frequency mechanical impact (HFMI) is an efficient post-weld treatment technique that enhances fatigue strength in metallic welded structures. Steel or steel-concrete composite road bridges, where the fatigue limit state often governs the design, compose one category of structures that can benefit from the application of this technology. To assert an improvement in fatigue strength using HFMI, the induced compressive residual stresses must be stable. Therefore, the maximum service stresses that can be allowed on HFMI-treated joints should be controlled to avoid the relaxation of the induced beneficial compressive stresses by HFMI treatment. Using statistical analysis of recorded traffic, this paper compares the measured maximum traffic loads to those generated by a load model. More than 870,000 and 470,000 recorded vehicles from traffic measurements in Sweden and the Netherlands are used in this analysis. To capture the characteristic bending moment, the daily maxima of the resulting measured load effect are combined with the extreme value distribution of the bending moment. In addition, it is found that the characteristic load combination is the best-studied option to assess the maximum stress in HFMI-treated weldments in road bridges.

Intermixing behavior of 1.4430 stainless steel and 1.4718 valve steel in in situ alloying using coaxial laser double-wire laser directed energy deposition

Coaxial laser wire directed energy deposition promises a direction-independent buildup of near net shape geometries and surface coatings. Simultaneously introducing two different wire materials into the processing zone enables the production of in situ alloyed or even functionally graded structures. Functionally graded materials and in situ alloyed parts aim to extend the range of materials for development purposes. This work covers the intermixing behavior of two wire materials with greatly differing element contents. Therefore, a multiple diode coaxial laser (DiCoLas) processing head is used consisting of three individually controllable fiber coupled laser diodes with a combined maximum output power of 660 W and a wavelength of 970 nm. Two metal wires, 1.4430 and 1.4718, with a diameter of 0.8 mm are provided simultaneously to the processing zone under an incidence angle of 3.5° to the processing head's middle axis. The DiCoLas processing head enables a stable welding process with good dimensional accuracy of the single welding geometries. Single weld seams and multiple-layer structures are investigated to cover the intermixing behavior for different applications of additive manufacturing. Thermal images of the melting process provide an insight into the melting behavior of the two wire materials and the formation of the weld seam. energy-dispersive x-ray-mappings and line scans display the element distribution of the main alloying elements along the seam cross section. Furthermore, hardness measurements examine the hardness progression along the multiple-layer welding structures showing an even progression of the hardness values over the entire cross section.

The effect of TIG welding on the structure and hardness of butt joints made of Inconel 718

The tests discussed in the article aimed to analyse the structure and hardness of the heat affected zone and that of the weld in thin butt joints (1.0 mm) made of Inconel 718 using the TIG method and variable welding linear energy restricted within the range of 45 J/mm to 80 J/mm. The test joints were subjected to visual tests, macro and microscopic metallographic tests, scanning electron microscopy-based structural observations and hardness measurements. The tests concerned with the effect of the TIG welding of butt joints made of 1.0 mm thick sheets (Inconel 718) in laboratory conditions revealed that the most favourable quality of the sheets was obtained when welding arc linear energy was restricted within the range of approximately 45 J/mm to 80 J/mm. An increase in linear energy within the above-presented range led to an increase in the width of the weld and that of the HAZ (observed in the joints subjected to macroscopic metallographic tests). In addition, an increase in linear energy restricted within the aforesaid range increased the grain size in matrix γ (in the HAZ) from approximately 10 μm–20 μm. The structure of the weld contained the zone of columnar grains oriented towards the fusion line as well as large groups of primary grains having the dendritic structure with clearly visible axes of primary dendrites of varied orientation. In addition, the weld structure also contained precipitates in the form of low-melting eutectics located in interdendritic spaces.

Damage detection in the T-welded joint using Rayleigh-like feature guided wave

Steel T-welded joint structures have been largely applied in aerospace and marine infrastructures. The weld length in T-weld joint structures is usually long, and it is difficult to access the weld conditions for damage detection purposes. This is due to the T-welded joint structure possessing a more complex cross-section than the conventional welded plate-like structures. Rather than formed by two plates and joined with a butt weld, the joint regions in the T-welded joint structure are connected to the sides of three plates to form a T-welded joint, and hence cannot be considered as plate-like structures. This makes guided wave modes difficult to be identified and exploited. This paper assesses the feasibility to detect weld defects on a steel T-welded joint structure using the feature guided wave (FGW) technique. FGW technique can provide a fast and long-range inspection for local topographical features, such as welded joints, offering great potential for effective screening of damages. Semi-Analytical Finite Element (SAFE) method is applied to acquire modal solutions in the waveguide. A new algorithm is developed to obtain FGW modes with both high energy concentration and low attenuation from the solutions of SAFE eigenvalue problem. One particular FGW mode with similar mode shape as the Rayleigh surface wave is identified, of which the propagation occurs only in the joint region with small attenuation. This FGW, labelled Rayleigh T-welded wave (RTW), is explored in comprehensive experimental and numerical studies to investigate the propagation and backward scattering characteristics regarding optimal excitation frequency and different sizes of weld defect. The numerical and experimental results are in good agreement. The outcome of the study confirms the capability and robustness of RTW in detecting small weld defects, which allows a long-distance and sensitive screening for the small weld defects at the joint region in the T-welded joint structure.

Fatigue properties evaluation of fillet weld joints in full-scale steel marine structures

This study investigated the fatigue behavior of fillet weld steel joints (including cruciform and T-welded joints) in marine structures based on experimental tests and finite element analysis (FEA). In cyclic tensile loading, fatigue failure of full-scale specimens consistent with in-plane failure mode of marine structures was validated with ultrasonic phased array testing (UPAT). The effect of incomplete penetration and weld profile on fatigue performance were analyzed based on traction structural stress method. The results showed that the failure mode of load-carrying cruciform joints would change when the incomplete penetration ratio p’/tr reached 0.91. And the concave weld profile is better choice for welded structures anti-fatigue design. In view of the complexity of fatigue performance evaluation of fillet weld joints in IIW and BS7608 standards, a unified master S–N curve covering different plate thicknesses, materials, and weld profiles was proposed.

Fatigue Life Improvement of Weld Beads with Overlap Defects Using Ultrasonic Peening

Welding defects are common during the production of large welded structures. However, few studies have explored methods of compensating for clear welding defects without resorting to re-welding. Here, an ultrasonic peening method to compensate for the deteriorated mechanical properties of overlap weld defects without repair welding was studied. We experimentally investigated changes in the mechanical properties of defective welds before and after ultrasonic peening. The weld specimen with an overlap defect contained a large cavity-type defect inside the weld bead, which significantly reduced the fatigue life. When the surface of the defective test piece was peened, the fatigue life of the weld plate was restored, resulting in an equivalent or higher number of cycles to failure, compared to a specimen with a normal weld. The recovery of mechanical properties was attributed to the effect of surface work hardening by ultrasonic peening and the change in stress distribution. Thus, ultrasonic peening could compensate for the deterioration of mechanical properties such as tensile strength, fatigue life, and elongation due to overlap defects, without resorting to repair welding.

A fatigue reliability assessment model for welded structures based on the structural stress method

Since many factors affect the fatigue life of welded structures and the relationships between them are complex, finding effective ways to improve the fatigue reliability of welded structures has always been a challenge for the industry. A fatigue reliability assessment model and design method for welded structures based on the structural stress method is proposed. According to the limit state equation of the model, the design-life fatigue reliability and the service fatigue reliability assessment approaches are presented. Then, a first-order second-moment method is employed to reveal quantitative fatigue reliability for welded joints and structures. The relationships between the fatigue reliability and the influence variables are used to analyze and improve the welded structure design. Fatigue reliability of T-joint examples was assessed by accounting for weld leg sizes, plate thicknesses, penetration depths, and single-sided and double-sided forms. Furthermore, the assessment model was verified with a welded bogie frame. The fatigue reliability of the frame was improved based on the evaluation results. The model and method can be applied to other types of welded joints and welded structures.

Qualification of digital twins for predicting failure in welded structures

Significant cost savings in Asset Integrity Management (AIM) are achieved by replacing condition-based with predictive-based maintenance strategies. However, this requires the gathering and analysis of huge amounts of real-time data from Structural Health Monitoring (SHM) sensors and periodic Non-Destructive Testing (NDT). This presents a problem that lends itself to Digital Twin (DT) Technology. In the case of process plant, DT technology has already been implemented using “Big-pipe” data from Condition Monitoring (CM) sensors to predict failures in pumps, compressors and other machinery on a company-wide scale. In the case of welded structures however, for example pressure vessels, pipelines and storage tanks, implementation of DT technology is hampered by a lack of confidence in the use of “Smallpipe” data from periodic NDT and continuous SHM. In “Big-pipe” data, data streams are very rapid flowing, with information directly available from the data. In “Small-pipe” data, data streams are very slow, accumulated over long periods of time and require careful interpretation to provide information for Engineering Critical Analysis (ECA) that is essential for predicting failure in the asset. This presentation will describe TWI’s approach to developing a DT for predicting failure in welded structures.

Feasibility study of shell element-based elastic FE approach for welding-induced thermal distortion prediction in HDPE welded structures

High-density polyethylene (HDPE) is considered an eco-friendly material for boat construction worldwide. However, managing thermal distortion in HDPE welding is challenging, impacting productivity. Traditional steel shipbuilding has established methods to predict welding-induced thermal distortion, but HDPE lacks comprehensive studies and standards. This research explores applying the elastic Finite Element (FE) approach, commonly used in steel structures, to HDPE welding. The elastic FE approach simplifies complex welding simulations, enabling its use in large structures like ship hulls. Our research assesses whether HDPE welded specimens exhibit similar distortion patterns to conventional welded structures and whether consistent parameters yield similar thermal distortion. Alignment between our FE analysis, based on specimen data, and experimental results validates the feasibility of using the elastic FE approach to predict HDPE thermal distortion. This study suggests it as a practical method to enhance HDPE boat manufacturing productivity.

Влияние собственных остаточных напряжений на сопротивление сварного соединения хрупкому разрушению

The influence of residual welding stresses on the probability of fragile destruction of a welded joint with a crack has been investigated. The process of elastic-plastic deformation of material in the region of the crack tip was investigated under the action of stretching and the field of residual stresses. The analysis of the stress state was made by the method of final elements, taking into account the elastoplastic properties of material. To take into account the random nature of the field of residual welding stresses, the statistical modeling method (Monte—Carlo method) was used. The methodology for accounting the residual stresses is proposed when calculating welded structures for resistance to brittle fracture. Based on the results obtained, the minimum temperature was evaluated, at which the first loading of the welded structure with a crack-like defect could be carried out.

Technical Commission on Welded Structure

Technical Commission on Welded Structure

Three-dimensional building of anisotropic gold nanoparticles under confinement in submicron capsules.

The low collision rate and contact time of gold nanoparticles (NPs) in solution afford a low welding probability, which hinders their welding structure, orientation, and dimension. Encapsulated anisotropic NPs, gold nanotriangles (AuNTs), were successfully assembled into a three-dimensional structure inside a permeable silica nanocapsule under light illumination to generate localized surface plasmon resonance (LSPR). AuNTs were trapped in the permeable silica nanocapsules and diffused in the nanospace because of copolymer release, which increased the contact probability of AuNTs and promoted the three-dimensional building of AuNTs. Electron energy loss mapping simulations revealed that the obtained three-dimensional AuNT structure exhibited spatially separated multiple LSPR modes with different energies of incident light, which are photophysically attractive beyond the facet-selective chemical growth of NPs, and postmodification for anchoring substances with site-selective attachment to the obtained structure will be applicable to expand the sensing design and class of substances for sensing.

MAXIMIZATION OF COMPRESSIVE STRENGTH IN TIG WELDING OF MILD STEEL USING RESPONSE SURFACE METHODOLOGY

Welding defects influence the desired properties of welded joints giving fabrication experts a common problem of not being able to produce weld structures with optimal strength and quality. In this study, fatigue was minimized using artificial intelligence such as the Response Surface Methodology An optimal design of experiment was developed which was used as a guiding plan to conduct the experiment., thereafter a second order polynomial l model was developed which was used to minimize the fatigue with very significant statistical results. The result shows that the quadratic model was the most suitable for minimizing the fatigue response with a P-value < 0.05

Вопросы сварки аустенитных сталей с высокой концентрацией азота (Обзор)

Alloying with nitrogen allows one to substantially increase the strength of steels, especially of the austenitic steels, in which the equilibrium nitrogen content can reach 0.4 – 0.7 wt % depending on their chemical composition. Nitrogen stabilizes austenite and enhances its corrosion and wear resistance. For this reason, nitrogen-containing austenitic steels are advantageous structural materials, in particular, for heavy loaded welded structures. However, wrong choice of the welding method, regime, or filler for high-nitrogen steels can cause critical defects such as pores and cracks in the welded joints and substantially decrease their mechanical properties and corrosion resistance compared to those of the base metal. More than hundred literature sources have been considered for the analysis of welding types and methods for austenitic steels containing ≥ 0.4 wt. % nitrogen, the criteria for their weldability, and the causes for potential negative phenomena occurring upon their welding. For such steels, information is provided on the welding filler materials as well as on the modes and parameters of the welding process (supplied heat, presence/absence of a protective atmosphere, its composition, etc.). The structure, phase composition, and properties of the resulting welded joints are considered. The examples are given on the effect of the subsequent processing of welded joints (heat treatment and thermal deformation processing for the elimination of the resulting distortion) on their basic properties.