Arc-welded Joints Research Articles

Numerical methods for calculating the structural reliability of fatigue-loaded welds

In this work, with the aid of the implicit gradient method, the fatigue behaviour of different types of arc-welded joints was analysed. The structural parts, made of steel, were modelled as three-dimensional solids without applying any geometric exemplification, directly calculating the fatigue life numerically. The advantage offered by this approach is that of being able to maintain the unvaried calculation procedure regardless of the type of joint in question. Moreover, adopting the gradient method, there is no obligation to impose particular rules for the creation of the calculation mesh on the finished elements.

Mechanical properties of ferritic stainless steel welds in using type 409 and 430 filler metals

In this study, feasibility of using typical ferritic filler metals (409LNb, 430LNb, and 430Ti) for welding of low and medium chromium ferritic stainless steels (EN 1.4003 and types 409, 430, and 441) was investigated. The paper concentrates on basic mechanical properties of gas metal arc-welded joints at ambient temperatures. A variety of mechanical testing, i.e., tension, microhardness, macrohardness, impact toughness, and Erichsen cupping tests, were carried out in order to clarify differences between the joints fabricated with these filler metals. Further, effects of postweld heat treatments on toughness and ductility were evaluated. Microstructures of the welds were analyzed using optical and scanning electron microscopy. According to the results, the tensile strength and ductility are acceptable, but the major limiting factor with these, as with other ferritic filler metals, is poor impact toughness in the weld region. Welds fabricated with the 430LNb welding wire had a ductile-to-brittle transition temperature (DBTT) above ambient temperature. The titanium-stabilized filler metal 430Ti can have improved impact toughness due to grain refinement. The poor impact toughness in the weld region is not seen in the formability of the weldments in Erichsen testing. Postweld heat treatments are beneficial only when welding the traditional type 430 steel. In fact, unnecessary postweld heat treatment runs the risk of decreasing the weldment toughness owing to Laves-phase embrittlement, particularly with type 441.

Modeling of Thermel Transport for GMAW

Investigation of temperature distribution of submerged arc welded plates is essential while designing submerged arc welding joint because the key parameter for the change of weld bead geometry dimension, thermal stress, residual stress, tensile stress, hardness, and so forth is heat input, and heat input is the function of temperature distribution of GMAW process. An attempt is made in this paper to find out the exact solution of the thermal field induced in a semi‐infinite body by a moving heat source with Gaussian distribution by selecting appropriate inside volume for submerged arc welding process. It has been revealed that for GMAW, best suitable heat source shape is a combination of semispherical and semioval.

Solution for Modeling 3D Moving Heat Sources in a Semi-Infinite Medium and Applications to Submerged Arc Welding

The determination of the temperature distribution of submerged arc-welded plates is essential when designing submerged arc-welded joints. The key role for the change of weld-bead geometry dimension, thermal stress, residual stress, tensile stress, hardness, etc., is heat input. Heat input is the function of temperature distribution of submerged arc welded plates. An attempt is made in this paper to find the analytical solution for a moving heat-source of egg-shape in a semi-infinite body. The considered modes of heat transfer for this study are conduction and convection. The solution has been obtained by integrating the instantaneous point heat source throughout the heat source volume. Very good agreement between the predicted and measured transient temperatures at various points on submerged arc-welded plates has been obtained. The predicted yield parameters are also in good agreement with the measured values.

Thermal Modeling of Multipass Narrow Gap Pulse Current GMA Welding by Single Seam per Layer Deposition Technique

A thermal model has been developed for production of multipass single seam per layer narrow gap pulse current gas metal arc (GMA) weld joint of thick plates free from lack of groove wall fusion under no angle of attack to groove wall. The model considers the fusion of groove wall as well as a part of earlier deposited weld based on the geometrical aspects and temperature of weld pool, which primarily arises out of initial arc heating and heating by droplets of superheated filler metal transferred to the weld pool. The geometrical aspects of weld pool are considered as its width and height appeared under narrow weld groove. For prduction of a sound weld joint, the favorable role of pulse current gas metal arc welding (P-GMAW) has been amply justified. But the selection of pulse parameter is quite complex due to involvement of relatively large number of pulse parameters simultaneously interactive in nature, which has been solved by considering a summarized influence of pulse parameters defined by a dimensionless hypothetical factor . The model is able to help in proper selection of pulse parameters prior to carrying out welding with appropriate groove wall fusion. The model is experimentally verified by preparing weld joints of high strength low alloy high-strength low-alloy (HSLA) steel using different combinations of pulse parameters.

Residual stress caused magnetic field abnormal change upon arc welding joints

Residual stress concentration of welding joints is an essential factor to structure safety. It was found that the residual stress could generate a change of magnetic field in arc welding. Things became simple because of the methods based on measuring the distribution of the surface fields and analyzing the relation between the fields and the stress. However, we believe the fact that the magnetizing field caused by electrical current in arc welding has effects can not be ignored. Also, the magnetic field of the Earth is sometimes considered as a critical point in the field's change. In this paper, experiments were carried out to study the role of arc current by comparing the methods of arc welding and laser welding. The magnetic field was measured upon the welding sites. By controlling the input energy, the residual stress was almost the same. The results obtained from these two welding methods varied. Magnetic fields testing from arc welding specimens were changed more sharply than the laser ones. This means that the magnetic change caused by electrical arc current is important to the surface field. Therefore, by analyzing the status of arc current, electro-magnetic methods can be used as non-destructive testing tool of the arc welding joints merely by testing the surface magnetic field without specific magnetization.

Statistics of Weld Geometry for Laser-Hybrid Welded Joints and its Application within Notch Stress Approach

During the past few decades the shipbuilding industry has shown an increasing interest in laser welding. In particular, laser-hybrid welding offers special advantages over arc welding such as low levels of welding distortion because of the different welding processes used. In the present study, the influence of weld geometry on notch stresses in butt-welded joints was studied experimentally and numerically using a notch stress approach. The results of hybrid-welded joints were compared to those of laser- and arc-welded joints. In the case of laser-based joints the weld height, weld width and notch depth are the dominant geometrical parameters. The flank angle of the weld has a minor influence, unlike in an arc-welded joint, because of the difference in the weld bead size. The weld dimensions showed a large statistical variation, and this resulted in significant differences in the stress concentration factor values between the critical and mean weld geometries. The analysis of fatigue test results indicated that the statistical variation of the weld dimensions should be included in the notch stress analysis in order to improve the accuracy of fatigue strength prediction.

Tensile and Impact Toughness Properties of Gas Tungsten Arc Welded and Friction Stir Welded Interstitial Free Steel Joints

Welded regions of interstitial free (IF) steel grades in the vicinity of weld center exhibits larger grains because of the prevailing thermal conditions during weld metal solidification. This often causes inferior weld mechanical properties. In the present study, tensile properties, charpy impact toughness, microhardness, microstructure, lowest hardness distribution profile, and fracture surface morphology of the gas tungsten arc welded (GTAW) and friction stir welded joints were evaluated, and the results are compared. From this investigation, it is found that friction stir welded joint of IF steel showed superior tensile and impact properties compared with GTAW joint, and this is mainly due to the formation of very fine, equiaxed microstructure in the weld zone.

Thermomechanical finite element analysis and experimental investigation of single-pass single-sided submerged arc welding of C—Mn steel plates

Determination of distortions are important while designing the arc-welded joints. These distortions occur in a varied way in almost every type of welded joint, depending on several parameters, i.e. welding speed, plate thickness, welding current and voltage, restraints applied to the job while welding, thermal history, etc. In the present work a numerical model based on the finite element package ANSYS was developed for single-pass single-sided submerged arc welding of square butt joints. Suitable macros were developed to simulate the situation of a moving distributed heat source, metal deposition to account for top and bottom reinforcements, a time step, and a meshing scheme. In this model the effect of bead geometry was incorporated. The effect of filler metal deposition was taken into account by implementing the element birth and death technique. Submerged arc welding (SAW) can be conveniently used to weld a range of plate thicknesses in a single run using a suitable backing strip achieving adequate top and bottom reinforcements. The welding methodology established in the present work resulted in minimizing angular distortions in butt welds. The numerical model yielded results comparing well with those of the experimental ones.

Effect of Autogenous Arc Welding Processes on Tensile and Impact Properties of Ferritic Stainless Steel Joints

The effect of autogeneous arc welding processes on tensile and impact properties of ferritic stainless steel conformed to AISI 409M grade is studied. Rolled plates of 4 mm thickness have been used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure, and fracture surface morphology of continuous current gas tungsten arc welding (CCGTAW), pulsed current gas tungsten arc welding (PCGTAW), and plasma arc welding (PAW) joints are evaluated and the results are compared. It is found that the PAW joints of ferritic stainless steel show superior tensile and impact properties when compared with CCGTAW and PCGTAW joints, and this is mainly due to lower heat input, finer fusion zone grain diameter, and higher fusion zone hardness.

외관검사를 통한 한국형 철근자동가스압접기의 압접성능 연구

This study is focused on the welding performance of automatic gas pressure welding machine adapted to korean construction site by external appearance investigation. As gas pressure welding is more economical and has good performances compared with other steel bar jointing methods, as arc welding and mechanical joint etc, in Japan, the gas pressure welding is one of the typical connection of steel reinforcement when connecting the D29 and thicker steel bars, But in Korea, gas pressure welding joint method is not widely used caused by the shortage of skilled workers. so to activate the gas pressure welding in Korea, the automatic gas pressure welding machine is developed. In this study, the welding performances of gas pressure welding joint samples using korean automatic gas pressure welding machine are measured by external appearance investigation - blown diameters, blown length, welding face disagreement, central axis eccentric ratio, bending, sag and crack. The results of welding performances on the gas pressure welding joint samples show that samples are satisfied with the standard value regulated in KS D 0244 and JIS Z 3120.

가스텅스텐아크 용접한 클래드(A4045/A3003) 알루미늄 합금의 기계적성질 및 미세조직

In this paper, research was the variation of microstructure and mechanical properties of clad(A4045/A3003) Al alloy sheet by gas tungsten arc welding. Tensile properties of the gas tungsten arc welding joint decreased because of the softened heat affected zone(HAZ). The hardness of HAZ was lower than that of base metal, because relieved the work hardening effect of the welding heat. Hardness distribution of the weld zone with the base metal appears similarly, but the hardness of HAZ decreased remarkably. The microstructure in the weld zone of A4045 clad layer was formed a coarse columner grains of Si-rich. In the case of large weld heat input, the Si of the A4045 were diffused and until A3003 weld zone they decreased the strength.

The study on the plasma arc weld bonding process of magnesium alloy

Abstract In this paper, a new welding method called the “plasma arc (continues) weld bonding” (PAWB) process was used to join magnesium alloy. The microstructure, elements distribution and failure load of the welding joint were observed and tested. The results showed that a welding joint without pores and inclusions could be obtained by the PAWB process. The fusion zone of the PAWB joint consisted of refined equiaxed grain, and the grain size was finer in upper fusion zone than that in bottom fusion zone. And the heat affect zone was not evident comparing with the plasma arc welding (PAW) joint. The PAWB joint showed the highest failure load among the PAW joint, adhesive bonding joint and itself.

Weld brazing of copper thick plates

The weld brazing of 6 mm thick copper plates without preheating was investigated. The weld metal of weld brazing is composed of α-Cu solid solution and Cu–Ag–P eutectic structure, and the α-Cu solid solution in the weld metal of weld brazing is larger than that in the brazing weld. The average hardness values within the weld are 60 HV (50 g) lower for weld brazing than for brazing. In all weld brazing specimens tested, the failure was located in the heat affected zone with a tensile strength slightly lower than the base metal but similar to the arc welding joints.

철근 가스압접공법 활성화를 위한 한국형 철근자동가스압접기 기술개발방향

The study is focused on the settling the developing direction of korean gas pressure welding machine which can be applied in korean construction sites with moderate and high performance. Gas pressure welding is more economical and has good performances than other steel bar jointing methods, as arc welding and mechanical joint etc. Therefore in Japan, the gas pressure welding, which has less loss of steel bars and low performance of joints, when connecting the D29 and thicker steel bars, Is one of the typical connection of steel reinforcement. But in Korea, the gas pressure welding method is not widely used caused by the shortage of skilled workers, and this situation in Korea can not be solved in short period. The training of the skilled workers takes long period(around <TEX>$6\~10$</TEX> years), and there is no certification system for gas pressure welding. So to activate the gas pressure welding in Korea, the development of the automatic gas pressure welding machine is necessary, which gives regular performance of the steel bar joints and can be operated by not sufficient skilled workers. The automatic gas pressure welding machine was developed in Japan, but this machine has many problems when applied in korean construction sites. Therefore, it is necessary to develop a korean automatic gas pressure welding machine to overcome this problems. To develop korean automatic gas pressure welding machine, the problems, which shows when applied in korean construction sites, need to be investigated. According to the investigation, counterproposals are presented for the pragmatical development of the korean automatic gas pressure welding machine.

自動車用高強度鋼板の溶接継手の疲労特性におよぼす溶接法の影響

In high strength steel sheets, it seems to be possible to improve the fatigue strength of joints welded by using laser welding due to the lower heat input of welding and the flatter weld beads compared with conventional welding methods such as arc welding or resistance spot welding. Therefore, in this paper, fatigue tests were conducted for the specimens with the butt joints of 780 MPa grade steel sheets welded by using laser welding, plasma welding and MAG welding and for the specimens flattened the weld beads to investigate the effect of welding methods on the fatigue properties of welded joints of high strength steel sheets for automobiles. And the macrostructure, the microstructure and the hardness distribution around the weld metal were observed to study the mechanism for the difference of the fatigue strength by the welding methods. It was found that the fatigue strength in arc-welded joints and plasma-welded joints is lower than that in laser-welded joints mainly due to the occurrence of softening in the heat affected zone. On the other hand, it was found that the stress concentration at the toe of the weld bead significantly deteriorates the fatigue strength even in the laser-welded joints.

Deformation and failure response of 304L stainless steel SMAW joint under dynamic shear loading

Abstract The dynamic shear deformation behavior and fracture characteristics of 304L stainless steel shielded metal arc welding (SMAW) joint are studied experimentally with regard to the relations between mechanical properties and strain rate. Thin-wall tubular specimens are deformed at room temperature under strain rates in the range of 8 × 10 2 to 2.8 × 10 3 s −1 using a torsional split-Hopkinson bar. The results indicate that the strain rate has a significant influence on the mechanical properties and fracture response of the tested SMAW joints. It is found that the flow stress, total shear strain to failure, work hardening rate and strain rate sensitivity all increase with increasing strain rate, but that the activation volume decreases. The observed dynamic shear deformation behavior is modeled using the Kobayashi–Dodd constitutive law, and it is shown that the predicted results are in good agreement with the experimental data. Fractographic analysis using scanning electron microscopy reveals that the tested specimens all fracture within their fusion zones, and that the primary failure mechanism is one of the extensive localized shearing. The fracture surfaces are characterized by the presence of many dimples. A higher strain rate tends to reduce the size of the dimples and to increase their density. The observed fracture features are closely related to the preceding flow behavior.

Dynamic Mechanical Properties and Fracture Behavior of a 304L Stainless Steel GTAW Joint under Shear Conditions

This paper employs the torsional split-Hopkinson bar to investigate the dynamic shear deformation behavior and fracture characteristics of a 304L stainless steel Gas Tungsten Arc Welded (GTAW) joint at room temperature under strain rates in the range of 8 � 10 2 s � 1 to 2:8 � 10 3 s � 1 . The experimental results indicate that the strain rate has a significant influence on the mechanical properties and fracture response of the tested GTAW joints. It is found that the flow stress, total shear strain to failure, work hardening exponent and strain rate sensitivity all increase with increasing strain rate, but that the activation volume decreases. The observed dynamic shear deformation behavior is modeled using the Kobayashi-Dodd constitutive law, and it is shown that the predicted results are in good agreement with the experimental data. Observation of the fractured specimens indicates that the fracture features are closely related to the preceding flow behavior. At all values of strain rate, it is noted that the specimens all fracture within their fusion zones, and that the primary failure mechanism is one of extensive localized shearing. The fracture surfaces are characterized by the presence of many dimples, which suggests a ductile fracture mode. It is shown the strain rate has a significant influence upon the appearance of the dimpled surface. A higher strain rate tends to reduce the size of the dimples and to increase their density. Finally, it is determined that the presence of weld inclusions also influences the appearance of the fracture. These inclusions cause the initiation of micro-voids, which grow and coalesce within the fusion zone, and eventually form a continuous fracture surface.

Re-weldability of neutron-irradiated stainless steels studied by multi-pass TIG welding

Weldability of neutron-irradiated stainless steel (SS) has been studied by multi-pass bead-on-plate and build-up tungsten inert gas (TIG) welding, simulating the repair-welding of reactor components. Specimens were submerged arc welding (SAW) joint of Type 304 SS containing 0.5 appm helium (1.8 appm in the SAW weld metal). Sound welding could be obtained by one- to three-pass welding on the plates at weld heat inputs less than 1 MJ/m in the irradiated 304 SS base metal. In the case of the build-up welding of a groove, no visible defects appeared in the specimen at a heat input as low as 0.4 MJ/m. However, build-up welding at a high heat input of 1 MJ/m was prone to weld cracking, owing to the formation of helium bubbles on grain boundaries of the base metal or dendrite boundaries of pre-existing SAW weld metal, in the area within 0.6 mm from the fusion line.

A Study of Fusion Zone Microstructures of Arc-Welded Joints Made from Dissimilar Aluminum Alloys

Arc welding has proven itself to be an economically affordable and efficient method for the joining of a wide variety of aluminum alloy structures that find extensive use in the industries of ground transportation and building construction. Welded joints, having a “T” configuration, in dissimilar aluminum alloys were produced using the semiautomatic arc welding process. In this study, a combination of a non-heat-treatable aluminum-magnesium alloy and a heat-treatable aluminum-magnesium-silicon alloy was successfully welded. Optical microscopy was used to characterize the fusion zone microstructures of the fillet-welded T joints. The intrinsic microstructural features and the development and presence of defects are highlighted.