Strength Of Welded Joints Research Articles

Investigation of the problems of existing methods of electric contact welding of rails and local heat treatment of welded joints

The article presents a statistical analysis of the operational cycle of welded joints of domestic and imported rails on all Russian Railways (JSC Russian Railways), which indicate insufficient reliability of welded joints. Statistical data on defective rails en route of JSC Russian Railways are presented as of 01.01.2022, 01.01.2023 and 01.01.2024. During contact welding of rails, parts of the welded rails are in two states: at the weld site, the metal is heated to a temperature exceeding the melting point of 1520 °C, where the metal melts and the metal is ejected from the weld, and in a plastic state in the HAZ. The ends of the rails are heated to temperatures below the solidus (for steel up to 1100–1200 °C), and under the action of a compressive force, they are plastically deformed by a certain amount (subsidence) and welded. The amount of upsetting, the compressive force, and the heating temperature of the rails have a decisive effect on the formation of the welded joint and are the main factors in the process of contact welding. Insufficient fatigue strength of welded joints has become increasingly evident when welding rails using the pulsed flashing method in steels alloyed with chromium and silicon. The high cooling rate of the HAZ leads to the formation of martensite areas that act as stress concentrators and subsequently to the possible formation of defects in welded joints, i.e. to the development of fatigue cracks in the foot, neck and head of the rail with subsequent brittle fracture. If the hardening technology is violated, the metal of the head of the welded joint spalls, and the softening of the metal during welding leads to the crushing of the metal of the head of the welded joint. Welded joints in rail strings must not have internal and external defects of a certain type that exceed the standard dimensions. As the speed of movement increases, the requirements for the straightness of the rails and welded joints increase.

Effect of Plate Thickness on the Laser-Welded Microstructure and Mechanical Properties of 22MnB5 Hot-Forming Steel.

To meet the development and application needs of advanced high-strength steel, the laser welding of 22MnB5 hot-forming steel plates with thicknesses of 2 mm, 3 mm, and 4 mm was studied in this paper. Mechanical testing revealed that as plate thickness increased, the tensile strength of welded joints decreased from 1489 MPa to 1357 MPa and 1275 MPa, equating to 96%, 91%, and 88% of the corresponding base metal strength, respectively. The heat-affected zone exhibited the lowest mechanical properties. Microstructural characterization showed that with increasing plate thickness, martensite grains in the welded joints grew larger, transitioning from fine acicular to larger island structures. Concurrently, dislocation density in the welded joints decreased gradually. Furthermore, microstructural changes in the heat-affected zone were more pronounced than those in the fusion zone. The larger grain size and reduced dislocation density softened the joint structure, which consequently decreased the strength and hardness of the welded joint. Laser-welded joints of three thicknesses can exceed 85% of the corresponding base metal strength, demonstrating strong industrial application potential.

Vibration Welding of PLA/PHBV Blend Composites with Nanocrystalline Cellulose.

Thermoplastic composites have garnered significant attention in various industries due to their exceptional properties, such as recyclability and ease of molding. In particular, biocomposites, which combine biopolymers with natural fibers, represent a promising alternative to petroleum-based materials, offering biodegradability and reduced environmental impact. However, there is limited knowledge regarding the efficacy of joining PLA/PHBV-based biocomposites modified with nanocrystalline cellulose (NCC) using vibration welding, which restricts their potential applications. This study demonstrates that vibration welding enables efficient bonding of PLA/PHBV composites with NCC, resulting in strong, biodegradable, and environmentally friendly materials. The investigation revealed that the addition of nanocrystalline cellulose (NCC) at 5, 10, and 15 wt.% significantly enhanced the strength of welded joints, with the highest strength achieved at 15% NCC content. Microstructural analysis using scanning electron microscopy (SEM) and deformation studies with digital image correlation (DIC) indicated that a higher NCC content led to greater local deformation, reducing the risk of brittle fracture. Mechanical hysteresis tests confirmed the composites' favorable resistance to variable loads, highlighting their stability and energy dissipation capabilities. Optimization of welding parameters, such as vibration amplitude, welding time, and pressure, is crucial for achieving optimal mechanical performance. These findings suggest that PLA/PHBV composites modified with NCC can be utilized as durable and eco-friendly materials in various industries, including automotive and packaging. This research presents new opportunities for the development of biodegradable high-strength materials that can serve as alternatives to traditional plastics.

Ultrasonic welding of CF/epoxy‐CF/PEI joints with enhanced vibration transfer efficiency and optimized welding quality

AbstractThis study investigated the impact of welding force on the ultrasonic welding quality of epoxy‐based to polyetherimide (PEI)‐based composite joints. PEI film layers were used on the carbon fiber/epoxy (CF/epoxy) composite surface through a co‐curing process, rendering it “weldable.” The ultrasonic welding for CF/epoxy and CF/PEI composite adherends were then performed, with varied welding force. The results showed critical effects of the welding force on the vibration transfer efficiency, morphology of welding lines and strength of welded joints. Lap‐shear strength (LSS) value of these joints initially increased and subsequently decreased with continuously increasing welding forces. Pore defects formed during the welding process were efficiently avoided while an optimal welding force was utilized, that resulted in the best quality welding line and the largest LSS of 39.4 MPa. In this case, CF/PEI and CF/epoxy composite adherends were cohesively failed, which was the main failure mechanism for the hybrid joints.Highlights Weldability of CF/epoxy composites was realized by co‐curing a PEI layer. Increasing welding force provided enhanced vibration transfer efficiency. Optimal welding force led to efficiently improved welding‐line quality. The largest LSS of 39.4 MPa was obtained with an optimal welding force.

Interface geometry modification to trap plasticized flash for improved joint strength of dissimilar rotary friction welds

Interface geometry modification to trap plasticized flash for improved joint strength of dissimilar rotary friction welds

Friction stir welding of similar and dissimilar Al and Cu lap joints: Effect of work piece material on conducive welding speed window, weld strength and hardness

This study used friction stir welding to make comparable (AA2219-AA2219 and Cu-Cu) and dissimilar (AA2219-Cu) lap joints. The tool retained its rotating speed at 1500 rpm and tilt angle at 2°, while welding speed varied from 23.5 mm/min to forward. Changing work-piece material affects welding speed, joint strength and hardness, and intermetallic compound formation. Similar lap joints have a welding speed window of 23.5–475 mm/min for Cu-Cu lap joints and 23.5–275 for AA2219-AA2219. However, dissimilar welding had a significantly smaller window of favorable speed: 23.5–30 mm/min for AA2219-Cu joints and 23.5–37.5 for Cu-AA2219 joints. The tensile strength analysis showed a maximum lap shear strength of ∼33 MPa for similar joints at extreme speeds, whereas dissimilar joints achieved ∼23 and ∼12 MPa for AA2219-Cu and Cu-AA2219 configurations, respectively, at 23.5 mm/min, mainly due to the formation of IMCs. Hardness testing indicated a significant increase to ∼79 Hv in dissimilar joints at 30 mm/min when copper was layered over AA2219, a result of extrusion and stirring effects. The high hardness in the dissimilar Al-Cu joints can be attributed to the formation brittle IMCs AlCu (Al2Cu) and Al4Cu9.

Influence of MIG Welding Process Parameters on the Strength of Bimetal Joints: Study of Gas Flow Rate and Macrofractures

Bimetal joints are often used in various industries, such as automotive, power generation, electronics, and manufacturing. This is because bimetal joints allow the joining of two types of metal with different properties. Welding two different types of metal can pose its own challenges, such as the difficulty of controlling welding parameters so that the results are optimal for both types of metal, as well as differences in the thermal and mechanical properties of the two metals. This has led to extensive research on bimetal plate connections. Based on this background, this research aims to determine the effect of variations in flow rate and current strength on the tensile strength of robotic welding bimetal welded joints, as well as determine the results of macro photos of fractures resulting from tensile tests for each variation. The research was carried out experimentally where each variation was repeated with data 3 times. Based on the results and discussion, it is known that the optimal gas flow rate in general is 20 l/min, where the tensile strength reaches 353.1442 MPa–455.5458 MPa. At this flow rate, the dominant fracture occurs in the base metal and is ductile, which indicates good plastic deformation. On the other hand, gas flow that is too low or too high causes joint defects and reduces the tensile strength. Meanwhile, other welding parameters, namely variations in welding current, affect tensile strength. At a gas flow of 10 l/min, increasing the current to 180 A produces the highest tensile strength of 449.4357 MPa with ductile fracture characteristics. However, at a current of 120 A there is a significant decrease due to overheating, especially at higher gas flows such as 20 l/min and 30 l/min, which results in brittle fracture in the heat-affected zone (HAZ). The results of this research contribute to the understanding of the influence of welding parameters on the tensile strength and fracture characteristics of bimetallic joints. This research can be a reference for the development of more efficient and reliable welding processes in various industries, such as automotive, power generation and manufacturing, which require bimetallic joints with optimal quality.

Stress state and strength of welded joints with V-shaped elements

It has been established that in the vicinity of V-shaped elements with a sharp apex, the stress field has a singularity of type σ→∞, which requires the use of the concept of “stress intensity factor” in strength calculations. This need arose due to different dimensions of the SIF and fracture toughness. Special criteria for the destruction of structures with V-shaped stress concentrators have been developed, which include, as special cases, the criteria of classical mechanics and the criteria of fracture mechanics. An experimental test of the proposed criteria and calculation methods was carried out. The information obtained is useful for analyzing welded joints on main pipelines and other equipment.

Enhancing resistance welding strength of carbon fiber/polycaprolactam thermoplastic composites through coupling agent‐modified metal heating elements

AbstractThis study investigates the impact of coupling agent‐modified resistance welding heating elements on the welding strength of carbon fiber‐reinforced polyamide 6 (PA6) thermoplastic composites. Silane coupling agent KH550 and titanate coupling agent UP‐201 were used to modify heating elements made of 304 stainless steel mesh. Optimal modification parameters for KH550‐modified stainless steel mesh (SSM) were determined using orthogonal experiments, resulting in maximum single lap shear strength (LSS) of 17.05 MPa under specific welding conditions. Comparative tests demonstrated the enhancement effect of UP‐201‐modified SSM on LSS. Additionally, two experimental schemes were used to study the synergistic enhancement effect of KH550 and UP‐201 on the LSS of resistance welded joints. The findings indicate that both coupling agents improve the welding strength, with significant differences in their individual and combined effects.Highlights This study explores carbon fiber reinforced Nylon 6, an innovative thermoplastic. Analyzed effects of modified heating elements on joint shear strength. Examined silane and titanate coupling agents' effects on weld joint shear strength. Investigated synergistic effects of silane and titanate agents on weld joint strength. Investigated the synergistic enhancement mechanism of silane and titanate agents.

Application of DFMA in lock band service modification of ATB-I3 building machine

The locking mechanism on the band service, known as the lock band service, is used to move materials to the tire-making machine. A building machine is a device that assembles components into partially finished or green tires. The components are tread, which acts as the tire tread, band/ply, which are fabric sheets coated in rubber, and bead wire. Subsequently, the materials are put together on the drum-mounted construction machine. The ATB-I3 machine has the largest downtime owing to a band service fault, with 840 minutes in January 2024, and is the problem with the highest downtime in section A2. The cause of the excessive downtime in the band service is an issue with the band service lock system, namely the pneumatic movement lock mechanism on the band service component. As a result, adjustments must be made by altering the lock band service's design. After that, a weld joint strength analysis is performed to make sure the modification can be safely put into practice. To obtain the optimal modification design, the DFMA method is employed. With the use of the DFMA approach, the updated design—which had a design efficiency value of 4.23% to 4.31% before—was improved. The welding connection in the updated design is safe to use since, according to the results of the welding connection calculation, the lock band service holder has a maximum welding load of 294,645.08 N whereas the actual welding load is 147,928 N. The reduction in service band downtime was tested with this improvement. Following the implementation of the update in March 2024, the amount of downtime resulting from damage to the band service dropped by 445 minutes, or 52.97%, to 395 minutes

Experimental and numerical study of dissimilar fiber laser welding of martensitic AISI 1060 carbon steel with different configuration with austenitic 304 and ferritic 420 stainless steel

Welding with fiber laser for two distinct stainless steel types was performed to join with the martensitic carbon steel (AISI 1060) in order to assess the effect of laser welding operating parameters for two dissimilar materials on the weld characterization thorough experimental design method and numerical investigation. A full central composite design (CCD) matrix in accordance with the response surface methodology (RSM) was developed to represent the responses variations by equations including quadratic and nonlinear interaction terms. Different laser welding parameters were taken into account, such as laser power, linear speed of welding, focal distance of the beam, and beam deviation. The responses considered were the temperature field next to the melt pool border line, the maximum penetration depth of the fusion zone and the ultimate tensile strength of the dissimilar weld joint. Additionally, the variation of the microstructure fusion zone and adjacent areas and failure mechanism of the weld joint were evaluated. The experimental results indicate that the temperature field measured at the vicinity of the melt pool fusion line with both 304 and 420 stainless steel which primarily influenced by the incident power of the laser and linear velocity of beam, respectively. Additionally, the numerical simulation results are in good agreement with temperature experimental results at vicinity of fusion line where the temperature measured, experimentally. Apart from this, at the center of the fusion zone, the temperature clearly predicts via numerical simulation results which is not possible to assess experimentally. A clear comparison between the temperature distribution with different joint configuration illustrates that distinct relation between the temperature variation rate and different thermal conductivity coefficient of AISI 1060 with different AISI 304 and 420 joint configuration resulted different temperature distribution. The weld joint microstructure for 420 stainless steel–AISI 1060 steel joint at fusion boundary zone consists of columnar dendrites and skeletal columnar ferrite. At the center of fusion zone, a cellular-type structure is seen. For 304 stainless steel joint, the fusion zone has composed of a remarkable part of skeletal delta-ferrite and dendritic microstructure at austenite matrix microstructure. The fracture section of 304 steel has a ductile fracture and the depth of fracture dimples and cavities toward 304 stainless steel are higher than AISI 1060 steel.

A New Approach for Enhancing Friction Welding Joint Strength

A New Approach for Enhancing Friction Welding Joint Strength

A Review of Bobbin Friction Stir Welding (BFSW) Process with Cooling Assisted Approach

Over the last two decades, friction stir welding (FSW) has emerged as one of the most promising technologies, especially when dealing with difficult-to-weld materials. FSW is frequently employed in the heat-treatable Auminum series and is applicable to alloys that are susceptible to heat damage during welding, which is a result of the advancement of solid-state technology. FSW is not a flawless process, and its limitations should be recognized. The constraints of this process must be identified and understood for better process improvement. Studies further concluded that bobbin friction stir welding (BFSW) minimizes these limitations. The bobbin weld usually begins with a slowly applied force on the edge of the base plate, moving at low speed until plastic deformation is realized. The welding speed then continues to advance with the introduction of higher speeds until an entire weld is formed. All the same, the BFSW welded joint strength is realized to be much below that of FSW. This is essentially attributed to the bobbin tool having a double shoulder, which generates a tremendous amount of heat. There is a restriction in the aspect of optimization, whereby it can be done just through the control of the process parameters. Therefore, this review paper endeavours to explain the role that cooling aids play in terms of joint strength, that is, the mechanical properties. The information gained from the summarization of technical information in this paper carries valuable insight into the approach of cooling-assisted BFSW and its respective parameters. Attention was focused on the basic ideas that go along with it, such as how heat is generated during welding and how process parameters affect mechanical properties, especially joint strength, which includes tensile strength and hardness. An increase in strength performance was exhibited where ordinary BFSW was inferior to the cooling-assisted BFSW, which was said to increase the joint tensile strength by 10%. This article is helpful to academics, researchers, and professionals in that it points out relevant features of the cooling-assisted BFSW process while identifying the future research that is required to be conducted.

Optimization of Welding Process for 825 Bimetallic Composite Pipes Based on Corrosion Testing

Abstract In the process of welding bimetallic composite pipe ring joints, a problem arises where the outer layer of carbon steel dilutes the inner corrosion-resistant alloy lining, resulting in a reduction in corrosion resistance. Therefore, selecting the appropriate welding process and parameters is crucial. This study established manual, semi-automatic, and fully automatic welding processes for welding 825 bimetallic composite pipes, conducted simulated corrosion tests on weld joint ring seams under sulfur-containing conditions, and performed comprehensive evaluations of physical and chemical properties, as well as corrosion resistance. The research findings are as follows: (1) There is a phenomenon of softening in the heat-affected zone of bimetallic composite pipe ring seams. Among them, the fully automatic welding method exhibits significant fluctuations in weld joint strength, higher toughness in the weld and heat-affected zone, and higher hardness values with less variation compared to other welding methods. (2) Under the manual, semi-automatic, and automatic welding processes, the intergranular corrosion rates are 1.08 mm/a, 1.64 mm/a, and 1.11 mm/a, respectively, and the pitting corrosion rates are 0.41 g/m2, 0.25 g/m2, and 0.31 g/m2, respectively. The uniform corrosion rates are 0.0002305 mm/a, 0.0002183 mm/a, and 0.0002197 mm/a, respectively. (3) High-temperature solution heat treatment (above 980 ° C for 30 minutes) can effectively promote the dissolution of carbides into the matrix, improving the intergranular corrosion resistance of alloy 825. The research demonstrates that under sulfur-containing conditions, weld joints obtained using the fully automatic welding process developed in this study exhibit better physical characteristics and corrosion resistance. This can effectively prevent corrosion failures and leakage incidents.

Welding Characteristics of Medium Titanium Plates with Autogenous Laser Welding and Narrow-Gap Laser Filling Welding Modes.

Titanium and titanium alloys with a medium thickness of 5 to 12 mm are widely used for ocean platforms, military equipment and in other fields because of their light weight, appropriate strength and corrosion resistance. In this study, autogenous laser welding and narrow-gap laser welding processes were researched and compared, and the welding characteristics, weld microstructure and joint strength were analyzed. The results showed that autogenous laser welding had higher efficiency, narrower weld width and higher microstructure uniformity. Autogenous laser welding can achieve the single pass weld penetration at laser keyhole mode. The weld width of narrow-gap laser welded joint was 12.5 mm, which was nearly three times than that of autogenous laser welding. The grain size of autogenous laser welding was obviously smaller and more uniform in depth than that of narrow-gap laser welding. In the weld zone, the coarse columnar α grains grew from the fusion line, while in the heat-affected zone, equiaxed α grains with needle and sawtooth α morphologies were presented. The microhardness of the heat-affected zone was higher than in the weld zone and the base metal due to the denser needle microstructure. The tensile samples all fractured at the base metal, indicating the welded joint strength efficiency was greater than 1.

Study on the estimation method for the mean stress effect on the fatigue strength of welded joints with various failure modes and joint types

In compact box-shaped steel structures, partial penetration welds are frequently selected as the welding technique, and root fatigue failure might manifest in these joints. In order to ensure the structural integrity of steel structures, it is necessary to develop an assessment approach for evaluating the efficacy of post-weld heat treatment (stress relief) in enhancing the fatigue strength of root-failed welded joints. In this study, bending fatigue experiments employing stress ratios of R = 0 and − 1 have been carried out on as-welded and stress-relieved welded joint specimens. The test objects include root-failed plug weld specimens, as well as toe-failed out-of-plane gusset weld joint and T-joint specimens. The welding residual stresses near the root notch and weld toe are measured by X-ray diffraction technique. The assessment of the mean stress effect on fatigue strength has been examined through the utilization of the modified MIL-HandBook-5D equivalent stress range. The equivalent stress range is evaluated by using two fatigue assessment stresses: structural stress and elastic–plastic local stress. It has been confirmed that all fatigue test results, irrespective of the failure mode or the joint type, whether from the as-welded or stress-relieved specimens, can be closely approximated using a single S–N curve with either definition of the equivalent stress. This outcome indicates the accomplishment of assessing the mean stress effect on the fatigue strength of welded joints with various failure modes and joint types.

Effect of peening treatment on fatigue strength of welded joints of aged steel

This study experimentally investigates the effect of peening treatment on the fatigue strength of welded joints of aged steel. Fatigue tests were conducted on T-shaped fillet welded joints made from three different types of aged steel under three-point bending loading conditions. To reveal fatigue strength improvement mechanism, residual stress measurement, hardness measurement, and metallographic analysis were performed at the weld toe for both as-weld and peened specimens. Fractured surfaces were examined to identify crack initiation sites and propagation. The findings reveal that peening treatment introduces compressive residual stress on the peened surface of welded joints of aged steel equal to or higher than conventional steel welded joints. Higher improvement of hardness was observed in the near surface of the peened welded joints of aged steel, and the improvement continued up to around the zero crossing points of the residual stress distribution. Additionally, peening treatment might refine near-surface grains of aged steel welded toe similar to conventional steel. The fatigue strength improvement effect of the peening treatment was the same for aged steel as conventional one. Cracks were observed on the peened surface of the aged steel due to over-peening treatment. However, it doesn't affect the fatigue strength improvement of the welded joints of aged steel. In summary, it can be said that peening treatment can improve fatigue strength of welded joints of aged steel in the same manner of conventional steel.

Microstructures and mechanical properties of laser-arc hybrid welded high-strength aluminum alloy through beam oscillation

High-frequency beam oscillation and synchronous wire-powder feeding were adopted for the laser-arc hybrid welding of a 2219-T6 high-strength aluminum alloy. Increasing the beam oscillation frequency from 0 to 250 Hz not only reduced the weld porosity from 2.64% to 0.16% but also promoted the transformation of columnar dendrites to fine equiaxed grains. In addition, the content of precipitated Al2CuMg increased with the refined size of the weld microstructure. The length of the columnar grains and the diameter of the equiaxed grains in the weld center were reduced by 40% and 50%, respectively. Owing to these improvements, the weld microhardness increased and became more uniform, and the variance decreased by 74%. The ultimate tensile strength and elongation of the welded joint reached 238.5 MPa and 4.3%, respectively, which were 26.5% and 105% higher than those of the non-oscillating hybrid weld, respectively. The weld tensile strength and the proportion of the area of the pore were negatively correlated. The porosity and microcracks of the welded joints were the main factors affecting the tensile strength of welded joints.

Optimization investigation of parameters for spot-welding of AA2014 and AISI316 dissimilar alloys

The objective of the research was to determine the exact process parameters required for spot-welding AA2014 and AISI316 alloys. The main focus was on achieving particular welding results, including nugget diameter, hardness, and tensile shear fracture load (TSFL). The central composite rotatable design model within the framework of a Response Surface Methodology (RSM) optimization approach, the study sought to intensify key spot weld process factors. The mechanical characteristics and nugget diameter of the welded joints were analyzed by carefully examining these factors to determine their significant effects. The investigation yielded crucial insights, revealing that the highest strength of welded joints, characterized by a nugget diameter of 5.982 mm, hardness of 149.6 VHN, and TSFL of 2.355 KN, was achieved at 3.4 kgf, when accompanied by 60 W power and a 2.5s duration. Notably, power emerged as the predominant factor driving the spot-welding process. Furthermore, microhardness and TSFL displayed direct correlations with power, while nugget diameter exhibited an inverse relationship. Moreover, rigorous statistical analyses, including F-tests and ANOVA, provided robust validation, indicating that the observed values fell comfortably within a 99.5% confidence interval for hardness, nugget diameter, and TSFL. These meticulously derived conclusions represent a significant stride towards establishing more standardized and efficient spot-welding protocols, particularly beneficial for the manufacturing sectors dealing with mild steel and aluminium materials.

A Comparative Study on the Performance and Microstructure of 304NG Stainless Steel in Underwater and Air Laser Welding.

In order to facilitate the application of underwater laser welding technology in in situ repairs of nuclear power plants, this study conducted comparative experiments between local dry underwater laser welding and laser welding in air on 304NG nitrogen-controlled stainless steel. The aim was to explore its microstructural evolution and mechanical properties in underwater environments. It was found that, near the fusion line of laser welding in air, columnar dendrites gradually evolved into cellular dendrites toward the weld center, eventually disappearing, resulting in a skeletal ferrite and serrated austenite structure. The underwater laser welding joints exhibited similar characteristics yet with more pronounced alternation between columnar and cellular dendrites. Additionally, the size of cellular dendrites decreased significantly, and needle-like ferrite was observed at the weld center. The hardness of underwater laser welded joints was slightly higher than that of in-air laser welded joints. Compared to laser welding in air, the strength of underwater laser welding joints increased from 443 MPa to 471 MPa, and the displacement increased from 2.95 mm to 3.45 mm, both types of welded joints exhibited a mixed mode fracture characterized by plasticity and brittleness.