Behavior Of Welded Joints Research Articles

Impact toughness behaviour of A516 GR. 60 steel welded joints

Impact fracture behaviour of welded joints made of A516 Gr. 60 is analysed as a commonly used carbon structural steel for welded structures. Impact testing on Charpy instrumented pendulum is performed using specimens with a notch at positions: the base metal (BM), heat-affected-zone (HAZ), and weld metal (WM). The total impact energy is presented as a sum of energies for crack initiation and crack propagation to make the analysis more sophisticated and comprehensive. The effect of temperature up to -60 °C was also analysed to prove the A516 Gr. 60 steel usability at subzero conditions.

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.

RESEARCH ON THE DESTRUCTION PROCESSES OF WELDED JOINTS UNDER CONDITIONS OF DETACHMENT OF THE VERTICAL STEEL TANK BODY FROM THE BOTTOM DURING A FIRE

The study presents a comprehensive analysis of welded joints by applying advanced mathematical modelling and experimental research methods. The primary objective was to develop and validate a methodology for mathematical modelling of the behaviour of welded joints under mechanical loading, as well as to assess the effectiveness of the proposed approaches in predicting their strength and durability. Based on the research results, we can draw the following conclusions. The authors obtained the results of welded joint samples and analysed the corresponding curves of the dependence of force factors on their deformations. The study showed that the destruction of welded joints occurs mainly along the weld seam, where the strength is lower than in the base material of the rods. It is consistent with the practical data of the experiment, which confirms that the weld is the weakest link in the structure. The article substantiated a set of provisions and assumptions for implementing mathematical modelling of the behaviour of samples of welded joints imitating welded joints in a reservoir for petroleum products under mechanical tensile tests. The test results justified the mathematical models of the steel material of welded joints of petroleum product tanks and obtained numerical parameters of the mechanical properties of steel of welded joints. Yield strength is in the range of 240–300 MPa, the modulus of elasticity is 190–240 GPa, the hardening modulus is 18–20 GPa, and the ultimate plastic deformation is 0.00334. Based on a complex of well-founded mathematical models of welded joints, we carried out calculations regarding the numerical study of the behaviour of welded joints under the conditions of their mechanical tests. We compared the obtained results with the results of experimental tests and, based on this comparative analysis, established that they were adequate since the Fisher criterion did not exceed the tabular value and the relative error did not surpass 12%. The findings of this research offer valuable insights and practical recommendations for improving the design and evaluation of welded structures, enhancing their performance and safety in engineering applications.

Investigation on the fatigue crack growth behavior of welded joints in EH690 high-strength marine steel

EH690 high-strength steel (HSS) is extensively utilized in marine engineering due to its exceptional strength. The fatigue crack growth (FCG) behaviors of EH690 HSS welded joints in different zones (base metal (BM), heat-affected zone (HAZ), and weld metal (WM)) were investigated by conducting FCG tests with various stress ratios (R). The results demonstrate that the WM and HAZ materials exhibit enhanced resistance to FCG compared to the BM material. The higher stress ratios result in increased fatigue crack growth rates (FCGRs). The welded residual stress (WRS) distribution in the welded joints was predicted considering solid-state phase transformation (SSPT). Subsequently, a comprehensive analysis of the WRS influence on FCG behavior shows that the residual compressive stress enhances the material’s resistance to FCG. Additionally, the effect of R on the FCG behavior of the material was investigated by employing the Walker model, and the applicability of the Walker model was discussed as well. Finally, the FCG mechanisms of the different zones in the welded joint were investigated from a microscopic perspective, further exploring the influence of R on the FCG behavior.

Behavior of welded joints on the roof truss of KOJK Office using LISA V.8 FEA

Behavior of welded joints on the roof truss of KOJK Office using LISA V.8 FEA

Study on interface diffusion and welding strength of Cu/Sn dissimilar metal electromagnetic pulse welding based on molecular dynamics simulation

The electromagnetic pulse welding (EMPW) method stands out for its rapid welding time, superior precision, and high automation, making it ideal for materials with significant melting point differences, specifically copper and tin, which often struggle to form robust joints. Utilizing molecular dynamics simulations, this study aims to investigate the interface evolution patterns under varying collision velocities and assess the welding strength of joints subjected to distinct tangential velocities. The findings reveal a profound correlation between the diffusion coefficient, system temperature, and the collision velocity during the simulated EMPW vertical collision. Specifically, at a collision velocity of Vz = 500 m/s, the interface tends to be linear, suggesting an unstable bonding state. However, when the collision velocity exceeds 700 m/s, a more intense diffusion of copper and tin atoms is observed, resulting in a wavy interface indicative of enhanced bonding capabilities. Furthermore, the study examines the shear behavior of welded joints subjected to oblique collisions with varying tangential velocities. The analysis reveals a transition in fracture locations from the joint-joint interface to the joint-base material interface and ultimately to the base material itself, as the tangential velocity increases from 50 m/s to 100 m/s and surpasses 200 m/s. This comprehensive evaluation of EMPW process variables provides a theoretical foundation for optimizing the mechanical properties of copper-tin EMPW joints.

Effects of random meso‐defects on fatigue behavior of welded joints: Damage evolution and lifetime prediction

AbstractRandom meso‐scale defects within welded joints can affect the structural damage process and cause dispersion in the fatigue lifetime of welded joints. In this paper, a meso‐scale stochastic damage approach is used to investigate the effect of random, meso‐scale defects on the fatigue damage lifetime of welded joints under different loads. First, we established an elastic–plastic fatigue damage model considering meso‐defects in the weld metal. Secondly, the fatigue lifetimes for gas tungsten arc welding and gas metal arc welding welded joints were predicted, with most of the predictions within the twofold dispersion factor. Thirdly, the Monte Carlo simulation method was used to investigate the influence of meso‐defect size on the fatigue lifetime dispersion degree, and the fatigue lifetime distribution under different loads was statistically analyzed.

Investigation on fracture resistance behaviour of dissimilar metal weld joint of modified 9Cr–1Mo steel and AISI 316LN SS

Fracture behavior of dissimilar metal weld joint consisting of mod. 9Cr–1Mo steel, AISI 316LN stainless steel, Inconel 82 butter layer and Inconel 182 weld has been investigated through experiments and FE simulations. The metallographic studies on weld joint and its interfaces have been carried out to determine the influence of microstructure on tensile and fracture properties. Tensile properties of different weld regions viz., weld metal, butter layer and HAZ have been evaluated using sub-size specimens. Fracture resistance behavior of weld joint has been studied through testing of compact type specimens with initial cracks machined at different locations. The plastic η factors for estimation of J-R curve have been obtained using FE analysis for crack in different regions viz., weld metal, butter layer and HAZ. Crack in weld metal exhibits lower fracture resistance as compared to butter layer and HAZ. Further, the constraint acting on crack and its susceptibility for deviation have been discussed in terms of stress triaxiality ahead of crack tip.

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.

Microstructure and Salt Spray Corrosion Behaviors of Welded Joints of 304/HRB400 Clad Rebars

Microstructure and Salt Spray Corrosion Behaviors of Welded Joints of 304/HRB400 Clad Rebars

Micro-macro modeling of tensile behavior of a friction stir welded hybrid joint of AlSi10Mg parts produced by powder bed fusion and casting

Additive manufacturing (AM) has gained considerable interest due to its ability to produce lightweight parts with hierarchical microstructures. However, the current constraints on the build chamber size in powder-bed fusion type AM processes limit its industrial application. A hybrid welded joint, consisting of an AM-processed and a conventionally manufactured part, can be employed to produce larger components. Due to the varying processing conditions, these hybrid welded joints contain a wide range of microstructural heterogeneities, which influences the mechanical properties of the joint. Using a numerical model to predict the mechanical behavior of welded joints by considering the microstructural variations is essential for the safe and reliable implementation of hybrid welded joints. This study aims to predict the local tensile behavior of each region of a hybrid friction-stir welded joint of AlSi10Mg produced by laser-based powder bed fusion and casting using a microstructure-sensitive model as well as the global tensile behavior by considering the properties of each region using a joint macroscopic model. The results from this modeling approach agree well with the experimental results. Therefore, this method can predict the mechanical behavior of hybrid welded joints and can establish the structure–property relationship in each weld region.

Role of Ti and Cr on microstructure and hydrogen embrittlement of welded joint of low-alloy steel used for armor layer

Welded joints suffer from hydrogen embrittlement (HE) owing to the internal stress generated during welding. Alloying elements play a vital role in the metallurgical behavior of welded joints. In this study, the influence of chromium (Cr) and titanium (Ti) on the HE behavior of welded joints in low-alloy steel was investigated by examining the microstructural morphology, grain characteristics, precipitate particles, engineering stress–strain curves, and fracture modes. The experimental results indicated that, compared with the addition of Cr, the addition of Ti promoted the formation of acicular ferrite in the lower fusion zone (FZ) via Ti-bearing oxides, and refined the grains of the FZ. The strength and elongation of the Ti joint were superior to those of the Cr joint in both air- and hydrogen-containing environments. Furthermore, compared with the addition of Cr, the addition of Ti improved the HE sensitivity. The fracture modes of both the Cr and Ti welded joints changed from ductile to brittle when the prepared joints were exposed to an H-containing environment.

Effect of water cooling assistance on fatigue behavior of laser welded QP980 steel

Quenching and partitioning 980 (QP980) steel has been applied to new energy vehicles, but even laser welding joints show poor fatigue performance. In this study, water-cooling assistance is applied to improve fatigue resistance of welded joints. Hardness, tensile and fatigue tests are performed together with microstructure observation (scanning electron microscope, transmission electron microscope and electron back scattered diffraction). It is found that tempering martensite showing low hardness and small average grain boundary angles are responsible for poor fatigue performance. Results show that water-cooling assistance significantly improves welding softening and fatigue crack growth behavior of welded joints.

Very High Cycle Fatigue of Welds: A Review

The design life of welded structures and components extends into the very high cycle fatigue (VHCF) regime across various applications. However, the availability of data on the fatigue behaviour of welded joints in the VHCF regime is limited, particularly when compared to the low and high cycle fatigue regimes. The development of ultrasonic fatigue testing equipment has accelerated fatigue testing and allowed for the VHCF properties of welds to be investigated in a feasible timeframe. In the present review, the emerging research concerning the VHCF behaviour of welds of various steels and non-ferrous alloys are individually explored. Overall, it is observed that welded joints have significantly lower fatigue strength than the base metal in the VHCF regime and that welding defects have a considerable influence on fatigue strength. Through the discussion of the relevant literature, important findings concerning the effects of specimen geometry and fatigue improvement methods are underlined. Furthermore, the guidance provided within design standards is compared, and some examples of VHCF failures of in-service components are highlighted. Finally, perspectives on future directions of investigation are put forward with the aim of encouraging further research in the field of VHCF of welds.

A novel elastic strain energy density approach for fatigue evaluation of welded components

The averaged elastic strain energy density (SED) within a characteristic volume radius R has been investigated and applied for characterizing the fatigue strength of welded joints for decades. However, engineering applications are still relatively rare. The main reason is that the calculation process is cumbersome due to fine mesh size and circular pattern requirements. This study proposes a novel approach of SED without requiring special finite element size and special layout requirements. First, a novel approach of the notch stress solution is presented. As a result, the present solution differs from the conventional approach which has been focused on notch tip singular stress field. Then, an averaged strain energy density can be obtained analytically by taking advantage of the new notch stress solutions presented in this study. Both the closed-form notch stress solutions and resulting expression for average strain energy density have been validated by FEA results. Subsequently, a large number of fatigue tests published in the literature are selected to examine the effectiveness of the evaluation approach of SED on interpreting fatigue behaviors of welded joints. Finally, a procedure for practical engineering application is established and verified by a group of fatigue tests of 3D gusset welded components.

CO2 Corrosion of X80 Steel under High Shear Flow Fields

Corrosion failure accidents owing to flow erosion and pipeline corrosion frequently occur during transportation. In this study, a high wall shear stress (WSS) experimental setup was established to conduct the online electrochemical corrosion test. The corrosion behavior of welded joints in NACE solution was studied by electrochemical experimental methods such as electrochemical impedance spectroscopy (EIS) and wire harness microelectrode (WBE). The results show that different areas of the welded joint show different corrosion phenomena in NACE solution. The weld metal (WM) has the significantly better corrosion resistance, while the base metal (BM) and heat-affected zone (HAZ) have worst corrosion resistance than WM. The current of the WM surface was cathodic current, while the current of the BM and HAZ surface were anode currents.

Morphological Characterization and Failure Analysis of the Ultrasonic Welded Single-Lap Joints.

Ultrasonic welding technology represents an advanced method for joining thermoplastic composites. However, there exists a scarcity of systematic investigations into welding parameters and their influence on the morphological characteristics and quality of the welded regions. Furthermore, a comprehensive experimental understanding of the welded joint failure mechanisms remains deficient. A robust model for simulating the failure behavior of welded joints under loading has yet to be formulated. In this study, ultrasonic welded specimens were fabricated using distinct welding control methods and varied parameter combinations. Diverse experimental methodologies are employed to assess the morphological features of the welded areas, ascertain specimen strength, and observe welding interface failure modes. Based on a cohesive model, a finite element model is developed to predict the strength of the ultrasonic welded joints and elucidate the failure mechanisms. The results showed that, under identical welding parameters, the specimens welded with a high amplitude and low welding force exhibit superior welding quality. The specimens produced under displacement control exhibit minimal dispersion in strength. The proposed finite element model effectively prognosticates both welded joint strength and failure modes.

Development and Improvement of Numerical Models of Welded Joints with Multiple Defects

This paper presents the development of numerical models which were used to simulate the behaviour of welded joints containing different combinations of multiple defects under tensile loads. Four representative combinations of defects were selected (including undercuts, incomplete root penetration, misalignments...), based on practical experience. In order to create accurate and functional models, this research involve a number of stages. This paper will focus on the various improvements made to the models, which started in relatively simple form. For this purpose, initial experimental and numerical analyses were carried out on specimens made of low-alloyed low-carbon steel S235, and after their accuracy was verified, the same methodology was applied to specimens made of higher quality material, steel S275. Improvements made to the models involved geometry, different combinations of boundary conditions and loads, and some were based on stress-strain states obtained by a combination of tensile testing and digital image correlation. The final result was a set of detailed numerical models which accurately simulated the behaviour of welded joints with multiple defects in them.

Multi-objective optimization of FSW aviation-grade AA8090 alloy: an RSM-based design approach

Purpose This study aims to determine the effect of different friction stir welding (FSW) parameters on mechanical and metallurgical characteristics of aviation-grade AA8090 alloy joints. Design/methodology/approach Response surface methodology with central composite design is used to design experiments. The mechanical and microstructure characteristics of the weld joints have been studied through a standardized method, and the influence of threaded pins on the joint microstructure has also been assessed. Findings From a desirability strategy, the optimum parameters setting of the friction stir welding was the tool rotational speed (TRS) of 800, 1,100 and 1,400 rpm; tool traverse speed (TTS) of 20, 30 and 40 mm/min; and tilt angle 1°, 2° and 3° with different tool pin profiles, i.e. cylindrical threaded (CT), square threaded and triangular threaded (TT), for achieving the maximum tensile strength, yield strength (YTS) and % elongation as an output parameter. The TRS speed was the highest weld joint characteristics influencing parameter. Peak tensile strength (378 MPa), percentage elongation (10.1) and YTS (308 MPa) were observed for the optimized parametric value of TRS-1,400, TTS-40 mm/min and TA (3°) along with CT pin profile. Microstructure study of the welded surface was achieved by using scanning electron microscope of output parameters. When the tool rotation speed, tool transverse speed, tilt angle and tool profile are set to moderately optimal levels, a mixed mode of ductile and brittle fracture has been seen during the microstructure analysis of the welded joint. This has been aided by the material’s plastic deformation and the small cracks surrounding the weld zone. Originality/value From the reported literature, it has been observed that limited work has been reported on aviation-grade AA8090 alloys. Further thermal behavior of welded joints has also been observed in this experimental work.

Microstructure and corrosion behavior of welded joint between 2507 super duplex stainless steel and E690 low alloy steel

Microstructure and corrosion behavior of welded joints between super duplex stainless steel 2507 and low alloy steel E690 were characterized herein. The joints are composed of base metal and heat affected zone (HAZ) of the two steels, weld metal, and dilution zone at the interface between weld metal and HAZ of E690 steel. Concentration gradients of Fe, Ni, Cr, and Mo exist between fusion boundary and Type-II boundary, and martensite band with a high hardness is formed. The changes of microstructure, element diffusion in different regions, and local acidification in E690 HAZ lead to heterogeneous corrosion attacks on the welded joints in artificial seawater. After long-term exposure, a corrosion groove is generated at the HAZ of E690 adjacent to the interface, where high stress corrosion cracking vulnerability is expected.