Welded Butt Joints Research Articles

Probabilistic reliability assessment of butt-welded joints under pressure using FAD and the FORM

Probabilistic reliability assessment of butt-welded joints under pressure using FAD and the FORM

Interface characteristics and fracture mechanism of laser-arc hybrid welded Al-Ti dissimilar butt-joint through beam oscillation

Two laser oscillating patterns including circle and inscribed double-circle were adopted for the laser-arc hybrid welding of Al-Ti dissimilar butt-joint, and compared with the none-oscillating hybrid welding. The results showed that a two-layer intermetallic compounds (IMCs) including Al3Ti and Al2Ti was formed at the Al-Ti interface without laser oscillation, and the thickness (τ) of IMCs layer reached up to 5.56 μm. The IMCs layer was transferred to a single-layer Al2Ti with decreased the τ to 1.18 μm by the optimized inscribed double-circle oscillating hybrid welding. The optimized laser oscillation benefited to form local turbulences inside the molten pool, which optimized the composition of interface IMCs layer and effectively reduced its thickness. Due to the combined improvements, the ultimate tensile strength of Al-Ti dissimilar butt-joint was increased by 18% from 182.6 to 215 MPa. The corresponding tensile fracture of welded joint changed from the two-layer IMCs layer to the base metal. Because no orientation relationship between them along the Al3Ti/ Al2Ti was formed, the tensile crack preferentially propagated between the Al3Ti and Al2Ti IMCs at the interface, resulting in the poor tensile properties.

Research on fatigue life of carbon fiber reinforced polymer strengthened single-sided butt welded joints utilizing resin pre-coating for strong adhesive bonding

Single-sided butt welding is a common connection method used in box beam structures such as excavator booms. Single-sided butt weld joints are prone to fatigue failure since the structures are subjected to cyclic loads over extended periods. The purpose of this study is to improve the fatigue performance of single-sided butt welded joints. Carbon fiber reinforced polymer (CFRP) strengthened single-sided butt welded joint specimens with permanent backing plates were prepared by pre-coating method, and constant-amplitude tension–tension fatigue tests were carried out on the specimens. The effects of welding groove parameters and CFRP reinforcement on fatigue life were studied. The test results show that the CFRP-strengthened specimens without blunt edges and with a groove angle of 40° show the highest average fatigue life. The single-sided bonding of 10 layers of CFRP sheets effectively inhibits the propagation of fatigue cracks and significantly improves the fatigue life of welded joints. In the CFRP/welded joint composite structure, the strain monitoring results show that the peak strain of the interface is the largest in the middle position, and the peak strain rises sharply in the rapid crack propagation stage, which indicates that the real-time interface strain peak can reflect the fatigue crack propagation. It provides an early warning method for real-time monitoring of fatigue life failure of welded structures in practical engineering.

Experimental and Numerical Characterization of Local Properties in Laser-Welded Joints in Thin Plates of High-Strength–Low-Alloy Steel and Their Dependence on the Welding Parameters

Laser welding on thin plates of high-strength steel is increasing in various industrial applications. The mechanical behavior of welded joints depends on their local properties, which in turn depend on the welding parameters applied to join the base material. This work characterizes the local properties of butt-welded joints of thin plates of high-strength–low-alloy (HSLA) steel. This study focuses on the effect of welding parameters on the microstructure, tensile response, microhardness, and weld bead profile. For this purpose, a factorial experimental design was formed, covering a heat input range from 53 to 75 J/mm. This study identified the main effects and interactions of welding speed and laser power on the weld bead profile and on its width. The microstructure, weld bead width, hardness, and tensile mechanical properties were significantly influenced by heat input. Furthermore, numerical simulations on real weld bead profiles revealed high values of the stress concentration factor and suggested a correlation with heat input.

Comparison of destructive and non-destructive fracture toughness measurements for Q235 steel butt-welded joint

As a critical component of a welded structure, the integrity of the welded joint significantly affects the safety and reliability of the structure in service. Therefore, it is essential to investigate the integrity of welded joints. However, given the harshness of standard measurements renders them unsuitable for application to small volume zones, welded structures or in-service structures. In this study, the fracture properties of a Q235 steel butt-welded joint was evaluated by boundary effect modelling (BEM) method and the ball indentation (BI) method. The results demonstrate that the fracture toughness distribution obtained by the two methods are consistent, with the highest fracture toughness in the weld metal, followed by the heat-affected zone and the base metal, and the lowest fracture toughness in the fusion zone, which is in agreement with the results of the metallographic testing. Furthermore, the relative errors of the zones obtained by the ball indentation method and the boundary effect modelling method ranging from 10.16 to 19.05%, which indicates safety margin ought to be considered for employing the BI method to determine fracture properties of in-service structures.

Structure and properties of the welded joint during arc welding of low-carbon steel under a layer of flux obtained from metallurgical slag of electric steelmaking

The results of the study of the influence of the thermophysical properties of the welding flux obtained by processing man-made waste of electric steelmaking (metallurgical slag) on the structure and properties of welded butt joints of thin-sheet low-carbon steel, with automatic arc welding on ceramic linings, are presented. Welding modes have been established using the developed flux, contributing to the achievement of seam sizes according to GOST8713–79, C4 joints, compliance with the mechanical properties of joints close to the base metal and ensuring a minimum level of welding deformations and stresses.

Fatigue life prediction for Q420qFNH weathering steel welded joints considering the effect of multiple cracks

Multiple semi-elliptical cracks frequently develop at the weld toes of welded joints. These interfering multiple cracks significantly accelerate crack growth rates and reduce the fatigue life of a welded joint compared to a single crack. This study proposes a method for predicting the fatigue life of a welded joint with multiple cracks, considering weld toe amplification effect, multiple crack interference amplification effect, and crack closure effect. The method is validated through fatigue tests on Q420qFNH weathering steel welded joints. The main factors influencing the interference amplification effect are investigated, and theoretical formulas for the interference amplification factor of the stress intensity factor are derived using the finite element method and the superposition principle. The initiation, aggregation, and morphological evolution during the propagation process of multiple cracks is accurately simulated, and the fatigue life of both cruciform-welded and butt-welded joints is predicted. Additionally, a quantitative analysis is conducted to assess the impact of the number of fatigue cracks on fatigue strength. The results indicate that the interference amplification effect of cracks depends on their distance and mainly affects the surface point where the crack front is closest. The proposed fatigue life prediction method can accurately estimate the fatigue life of Q420qFNH steel welded joints considering the effect of multi-cracks. The interference and coalescence of multiple cracks significantly reduce the fatigue life of welded joints. An increase in the number of fatigue cracks notably decreases the fatigue strength.

Fatigue research of metro car body based on operational loads

PurposeThe principle of infinite life design currently directs fatigue resistance strategies for metro car bodies. However, this principle might not fully account for the dynamic influence of operational loads and the inevitable presence of defects. This study aims to integrate methods of service life estimation and residual life assessment, which are based on operational loads, into the existing infinite life verification framework to further ensure the operational safety of subway trains.Design/methodology/approachOperational loads and fatigue loading spectra were determined through the field test. The material test was conducted to investigate characteristics of the fracture toughness and the crack growth rate. The fatigue strength of the metro car body was first verified using the finite element method and Moore–Kommers–Japer diagrams. The service life was then estimated by applying the Miner rule and high-cycle fatigue curves in a modified form of the Basquin equation. Finally, the residual life was assessed utilizing a fracture assessment diagram and a fitted curve of crack growth rate adhered to the Paris formula.FindingsNeither the maximum utilization factor nor the cumulative damage exceeds the threshold value of 1.0, the metro car body could meet the design life requirement of 30 years or 6.6 million km. However, three out of five fatigue key points were significantly influenced by the operational loads, which indicates that a single fatigue strength verification cannot achieve the infinite life design objective of the metro car body. For a projected design life of 30 years, the tolerance depth is 12.2 mm, which can underscore a relatively robust damage tolerance capability.Originality/valueThe influence of operational loads on fatigue life was presented by the discrepancy analysis between fatigue strength verification results and service life estimation results. The fracture properties of butt-welded joints were tested and used for the damage tolerance assessment. The damage tolerance life can be effectively related by a newly developed equation in this study. It can be a valuable tool to provide the theoretical guidance and technical support for the structural improvements and maintenance decisions of the metro car body.

Influence of tool rotational speed in butt-joint friction stir welding (FSW): a thermo-mechanical simulation of AA6061

Friction Stir Welding (FSW) is a solid-state welding technique that involves joining two pieces of material by rotating a non-consumable pin at high RPM. This rotation generates heat through friction between the tool and the plates, enabling the welding process without the need for filler metal. Invented by the British Welding Institute (TWI) in 1991, FSW is renowned for creating strong welds and is widely used in the automotive and aerospace industries, in those industries the aluminum alloys are indispensable due to their unique combination of properties. This study focuses on how variations in rotational speed influence temperature distribution, the width of the heat-affected zone, and Von-Mises stress distribution in welded aluminum alloy 6061 sheets, this research aims to provide a comprehensive understanding of these effect, therefore the findings are expected to contribute to optimizing FSW parameters and enhancing weld quality. The analysis was conducted using the finite element method and ALTAIR software.

Thick-wire GMAW for fusion welding of high-strength steels

The paper describes a high-current Gas Metal Arc Welding (GMAW) process using wire electrodes with diameters up to 4.0 mm for single-pass full penetration butt joint welding of 20 mm thick steel plates. Fundamental research aims to develop thick-wire GMAW into a high-efficiency method by identifying the limits of welding performance and achievable deposition rates. Current gaps in understanding include equipment requirements, process properties, application fields, and weld quality. The research project addresses these gaps through systematic investigations of basic technological analyses, application sample welding, and quality evaluations. The objective was to create a robust, cost-efficient gas-shielded high-performance welding technology with deposition rates comparable to Submerged Arc Welding. The fully mechanized, automatic welding setup included two parallel-connected welding power sources, one wire feeder and one high-power welding torch. Welding parameters and conditions were evaluated with the aim of achieving a high-quality weld. Optimal parameters were identified for one-sided single-pass welding on 20 mm thick plates. Validation of thick-wire GMAW for 20 mm thick high-strength steels was conducted via two-sided single-pass welding on S690Q grade plates. Testing of the weld joint included static tensile strength test (3x tensile specimen), a Charpy impact test at −40 °C (6x Charpy V-notch specimens respectively with notch position in weld metal, base material and heat-affected zone (HAZ)), microstructure examination and a hardness test. The lowest recorded impact energy was observed to be 50 J within the weld metal, in combination with hardness peaks in the HAZ reaching 415 HV1, and all tensile specimens failing outside the HAZ within the base material. The process achieved reliable, reproducible, and economical joint welding, meeting necessary mechanical-technological quality standards. The paper enhances the understanding of selected welding techniques tor thick plate joining and offers valuable industrial insights, demonstrating the technique's applicability and feasibility for high-strength applications.

Effect of weld-line position on springback behavior in advanced high-strength steel tailor-welded blanks on hat-shaped bending application

In this study, both experiments and finite-element analysis are performed to elucidate the effect of weld-line position on the springback behavior of advanced high-strength steel tailor-welded blanks (AHSS-TWBs). AHSS-TWBs are fabricated from grade 590Y high-strength steel and 980Y advanced high-strength steel, each with a thickness of 1.2 mm. Gas tungsten arc welding is performed to obtain autogenous butt-weld joints. Three distinct weld-line position patterns are systematically analyzed to investigate the springback phenomenon via hat-shaped draw bending. Experiments on the AHSS-TWBs show that the weld-line position affects springback. The stress distribution changes with the weld-line position, thereby initiating variations in both the components of the bending moment and the corresponding springback angle. Depending on the weld-line position, different springback behaviors and bending moments are resulted on the components.

Laser Welding of ARMOX 500T Steel.

The article describes the results of the study on laser welding of armor plates with a nominal thickness of 3.0 mm. The plates were made of Armox 500T steel characterized by a hardness of up to 540 HB, a minimum yield strength of 1250 MPa, an ultimate strength of up to 1750 MPa, and an elongation A5 minimum of 8%. The laser used for the welding tests was a solid state Yb:YAG laser. The influence of basic parameters such as laser output power, welding speed, and focal plane position on the weld geometry was determined during bead-on-plate welding tests. The optimal conditions for butt joint welding were determined, and the test joints were subjected to mechanical and impact tests, metallographic analysis, and hardness measurements. It has been shown that it is possible to laser weld Armox 500T armor plates, and at the same time it is possible to provide high quality butt joints, but this requires precise selection of welding parameters. A decrease in HAZ hardness of about 22-35% in relation to the hardness of the base material, ranging from 470 to 510 HV0.2, was found. The ultimate tensile strength of the test joints was approx. 20% lower than the Armox 500T steel. The bending tests revealed the low plasticity of the tested joints because the bending angle was just 25-35°. The results of Charpy V-notch test revealed that the impact toughness of the weld metal at -20 °C was approx. 30% lower than at room temperature.

A fatigue crack tip field model considering residual stress and plasticity-induced closure for welded structures

In order to more accurately understand and predict the fatigue crack growth behavior in welded structures, a fatigue crack tip field model considering residual stress and plasticity-induced closure (RSPC model) is presented in this paper. Building upon the existing CJP model, which adequately explains plasticity-induced crack closure, the RSPC model further considers the influence of tensile residual stress induced by welding. The model, through a detailed derivation and analysis of the residual stress function, establishes the theoretical stress and displacement fields at the crack tip of the butt-welded joint. Integrating these fields with the CJP model, the theoretical framework of the RSPC model is formulated. Subsequently, through fatigue crack growth experiments and digital image correlation analysis, a comparison and validation of the predictive performance of the CJP and RSPC models are conducted. It is observed that the latter aligns more closely with experimental results in calculating plastic zone area, with a maximum error of only 10%. In comparison to the CJP model, the average error decreases by 19.143%, indicating higher predictive accuracy. Furthermore, the study focuses on the contribution of tensile residual stress in butt welded joints to the growth of the plastic zone at the fatigue crack tip and the underlying reasons for its variations. Finally, the research investigates the constrained relationship between plastic zone size and fatigue crack growth rate. Corresponding relationship functions are fitted, providing more accurate guidance for crack control and material design.

RETRACTED ARTICLE: Investigating the strength of butt-welded joints of AA6082 and AA5052 alloys through friction stir welding; the impact of tool tilt angle and feed rate

We, the Editors and Publisher of the Journal of Adhesion Science and Technology, have retracted the following article: Investigating the strength of butt-welded joints of AA6082 and AA5052 alloys through friction stir welding; the impact of tool tilt angle and feed rate. Journal of Adhesion Science and Technology, https://doi.org/10.1080/01694243.2023.2253631. Bhiksha Gugulothua, Rajasekaran Saminathan, A. Pradeep, Ankit Sharma, S. Vijayakumar, Prabhu Paramasivam, and N. Srinivasa Rao. (2023). Since publication, concerns have been raised by a third party about the integrity of the data presented in the article, as well as potential authorship concerns. When approached for an explanation, the authors have been unable to provide their original data to verify its authenticity. In addition, the authors have not fully responded to our questions regarding the process of the research conducted. We have been informed in our decision-making by editorial policies and the COPE guidelines. The retracted article will remain online to maintain the scholarly record, but it will be digitally watermarked on each page as ‘Retracted’.

Effect of Corrosion and Post-Weld Treatment on the Fatigue Behavior of Multipass Robot GMAW Welds of S700MC Steel

High-strength steel is a candidate material for offshore structures, which are currently being constructed with regular-strength steel. These structures are constantly exposed to harsh environmental conditions and experience cyclic loadings, which can lead to premature failure due to the synergistic effects of corrosion and fatigue. In this regard, the current study aims to investigate the effects of corrosion and High-Frequency Mechanical Impact (HFMI) treatment on the fatigue behavior of welded joints made of S700MC steel. Multipass butt-welded joints were fabricated via the Robot GMAW method at an optimally selected heat input of 0.7405 kJ/mm. The microstructure of the weldments was studied using light optical microscopy. Tensile and Vickers microhardness tests were performed to evaluate the mechanical properties of the welded joints. To simulate marine environment corrosion in the laboratory, the as-welded samples were exposed to salt fog spray for 720 h. Subsequently, specimens were subjected to cyclic loading to evaluate their fatigue strength, while SEM and stereomicroscopy were used to analyze the fractured surfaces, providing a comprehensive understanding of the fracture mode. The findings suggest that although corrosion led to increased surface roughness and the formation of corrosion pits, its influence on the fatigue behavior of the weldments might be less significant compared to other geometrical factors, at least for the exposure time employed in the study.

Fatigue crack evaluation of butt weld joints in full-scale aluminum alloy joints: Experimental and numerical study of traction structural stress

In this study, the digital image correlation technique is used to determine the inconsistent mechanical properties and microstructure non-uniformity in different regions of aluminum alloy butt welded joints. A state monitoring method is proposed based on phased-array ultrasonic total focus imaging for crack evolution. A series of surface fatigue crack propagation tests on full-scale aluminum alloy butt welds are investigated, which innovatively revealed the mechanism and evolution law of crack propagation at the surface of the weld. The analytical function for dynamic crack propagation in welded structures is proposed, which provides a new idea and data support for clarifying the state deterioration process of structures. The results show that the traction structural stress can effectively identify the critical fatigue position of the weld and effectively account for the effect of angular misalignment. The phased-array ultrasonic total-focus imaging monitoring analysis method for surface fatigue crack propagation is proposed to improve the completeness of the fatigue crack evolution law.

Enhancing hardness in SMAW welded joints with low-frequency vibration assistance: an experimental and analytical study

Vibration assisted welding has gained popularity over the years for creating high quality welds and achieving better mechanical properties. The main objective of this research is to use low frequency vibration-assisted welding to optimise the process parameters. This study uses a novel vibratory technique to vibrate the workpiece during shielded metal arc welding at frequencies ranging from 0 to 100 Hz in order to examine the hardness of mild steel plates butt-welded to a thickness of 5 mm. Taguchi Methodology has been applied to optimise the hardness of welded specimens by varying the input variables viz. Current, vibration duration, and vibration frequency. Additionally, the microstructure of welded mild steel plates has been studied using SEM, optical micrographs, and XRD analysis. Results indicated that a low heat input of 80 Amp frequency of vibration of 100 Hz, and duration of vibration of 100 sec demonstrated optimum performance in terms of hardness of welded MS plates. Frequency of vibration has been found to be the most important parameter determining the hardness of the welded joint. Maximum hardness of 97.1643RHN has been found at optimal parameters. As the weld pool is being excited, vibration-assisted welded butt joints exhibit a finer grain structure, suggesting higher hardness values.

Fatigue properties of titanium-clad bimetallic steel butt-welded joints

Titanium-clad (TC) bimetallic steel is a high-performance constructional material that yields promising application potential in future ocean and coastal civil engineering. However, the understanding on the mechanical behaviors of the corresponding weld joints is still limited. In this paper, a tensile-tensile fatigue experimental study was conducted on two types of butt-weld joints fabricated of hot-rolled TA2 +Q355B TC bimetallic steel. Based on the test results, the fatigue stress-life curves (S-N curve) of the two types of weld joints were obtained and subsequently compared with that of TC parent materials, other representative structural metals, that of butt-weld on other metals and the codified S-N curves provided by six structural/fatigue design standards. Most specimens of the two types of TC weld joints are initially cracked at the clad-to-cap weld. The bonding strength between clad and substrate layers exhibit a promising reliability under fatigue loadings. The fatigue resistance of the two types of TC weld joints is considerably less than the different TC parent materials studied. The fatigue lives of clad material (TA2) and substrate material (Q345/Q355B) are greater than that of TC weld joints. The S-N curves of two TC weld joints are considerably lower than that of high-strength steel series but higher than that of aluminum alloy 6061-T6. The design S-N curves of EC3 (Class 36) and IIW (Class 36) are too conservative for the two TC weld joints.

Fatigue experiment and assessment of Q420qFNH weathering steel in the unequal-thickness butt-welded joint

The use of unequal-thickness butt-welded joints is widespread in bridge engineering, material savings mean a decrease in cost, which can lead to lower overall costs and significant benefits Because of their unique structures and propensity for stress concentration and weld defects, it is crucial to investigate their fatigue performance. In this study, 15 sets of unequal-thickness butt-welded joints based on Q420qFNH were subjected to fatigue tests. ABAQUS modelling and a stress-extraction process utilising distance iterations were employed in this study. The key findings demonstrated that the fatigue performance of these weathering steel butt joints was superior, and the stress variation at these joints exhibited greater complexity and resulted in a more pronounced multi-crack fusion effect. Additionally, an attempt was made to evaluate the fatigue behaviour of other welded joints and unequal-thickness butt-welded joints using the same approach as that presented herein. The fatigue evaluation method based on nominal stress yielded a significant scatter of 1:Ts = 4.21. Iterations were conducted based on the scattering at various critical distances. The results indicate that based on the theory of critical distance, the scatter of 1:Ts = 2.304 is lower than the scatter of 1:Ts = 2.502 associated with the notch stress method. These findings suggest that employing this method for fatigue assessment yields favourable outcomes across diverse welded joints.

Resilience-based seismic design and cyclic behavior of assembled joints between self-compacting concrete-filled rectangular steel tube frame columns and H-shaped steel beams

The overall stability of prefabricated steel structures depends significantly on the strong seismic resilience exhibited by the connections between beams and columns. This paper introduces a novel beam–column connection approach, referred to as the welded upper and lower flanges and two diagonal web plates (WULF-TDWP). Unlike conventional methods, this approach replaces bolted connections with butt-welded joints between steel beams and employs short cantilever beams to achieve plastic hinge displacement. The steel-column cross-section was designed with a larger aspect ratio to better absorb and distribute energy. Six full-scale specimens were subjected to cyclic loading tests to investigate the seismic performance of the WULF-TDWP system. The main test parameters included the axial load ratio, welding configuration in the node region, and presence of reinforcement plates. The specimens exhibited two distinct failure modes: plate buckling deformation and beam–column end weld tearing. The experimental results included the hysteresis curves, skeleton curves, ductility coefficients, stiffness degradation curves, and strength degradation curves of the specimens. The experimental findings highlighted the favorable hysteresis performance, load-carrying capacity, and deformation capacity of all the nodes. Additionally, the plastic hinges were observed to shift, thereby delaying the premature failure of the node region. Notably, the omission of welding between the cantilever short beam flange and steel column significantly reduced the initial stiffness of the node. Through finite element analysis, the seismic performance of the beam-column joints with upper and lower flange welded connections and cantilever short beams was elucidated. The reliability of the finite element model for assessing the seismic performance of the nodes was confirmed through validation using experimental findings. Furthermore, this paper categorizes the nodes and introduces a simplified calculation model based on the moment–rotation method.