Longitudinal Weld Research Articles

Experimental Investigation into the Capacity of Concentrically Loaded Steel Connections with Pretensioned High-Strength Bolts and Longitudinal Fillet Welds in Combination

This paper presents the results of an experimental study aiming to investigate the behavior of steel connections that combine pretensioned high-strength bolts and longitudinal fillet welds on a common faying surface. A total of 75 double-shear tension splices were tested under direct tension loading to quantify the effect of various connection variables on the load-deformation behavior of the connection. These variables include the (1) bolt pattern (2×2 and 2×3), (2) bolt size (3/4 in. and 1 in.), (3) bolt grade (ASTM F3125 Grade A325, A490, and F1852), (4) bolt pretensioning method (turn-of-nut and tension control bolts), (5) faying surface class (Class A and B), and (6) weld/bolt strength ratio. The variation in the connection characteristics covered a wide range of weld/bolt strength ratios from 0.50 to 2.00. The bolts were installed in oversized holes, and the specimens were assembled in a negative bearing condition to allow for a maximum slip distance. The load-deformation behavior of the combination connections was recorded and compared to that of the bolted- and welded-only control specimens. In all tests, the addition of welds increased the capacity of the connection. The investigation shows that the capacity of the combination connection with pretensioned high-strength bolts and longitudinal fillet welds can be computed by adding the capacities of the individual connecting elements while considering the strain compatibility.

Reasons for formation of transverse cracks in longitudinal weld of a pipe of the main gas pipeline

Investigations of transverse cracks in a longitudinal weld of a main gas pipeline pipe are presented, and the reasons for the formation of defects are analyzed. A comparative analysis of the results of in-line diagnostics and additional non-destructive testing with the actual parameters of cracks in microsections was carried out. The microhardness of the weld metal was measured in the crack zone and at a distance of up to 20 mm from it in both directions, which showed the presence of residual stresses in the region of the crack tip. The methods of optical and electron scanning microscopy were used to study the crack zone with the determination of the chemical composition of the weld base metal and inclusions in the crack zone. The results obtained made it possible to classify defects as “cold cracks” that formed in the weld metal after a long period of operation and developed further according to the stress corrosion cracking mechanism.

Imperfection Sensitivity of Large Cylindrical Shells Under Vacuum Considering Different Geometric Ratios

AbstractThe prediction of the buckling resistance of shells is subject to uncertainty since it depends significantly on the initial geometric imperfections caused by the fabrication process. However, the load case of vacuum or uniform external pressure has not yet been extensively studied. Stress design approaches implement a reduction factor alpha that accounts for the effect of imperfections. This factor is assumed to be a general lower bound but does not account for different geometric ratios. However, it is to be expected that different imperfection sensitivities prevail for different cylinder lengths or length to thickness ratios. To better understand this aspect, a comprehensive numerical study of buckling resistances of imperfect cylindrical shells is conducted, which covers a range of different length, radius and thickness ratios with focus on thicker and shorter cylinders. Within this study, three different geometric imperfection forms are investigated: linear bifurcation eigenmodes, and ovalisation and weld depressions, which represent typical imperfections of manufacturing processes. Further, a formulation for longitudinal weld depressions is introduced, since this direction of the imperfection is more deleterious than axisymmetric circumferential weld depressions. The results of this comprehensive study contribute to understanding the effect of different imperfection forms and amplitudes on different cylinder dimensions.

Interfacial bonding mechanism and length evaluation method of the longitudinal welds in the unsteady deformation process of porthole die extrusion of aluminum alloy profiles

In this work, a porthole die extrusion experiment was carried out on an aluminum alloy profile used for air-conditioning refrigerator ice box. Microstructural characterization and mechanical property tests were performed at different positions of a longitudinal weld in the profile head. The results indicated that, from the unsteady to steady extrusion stage, the number, sizes and depths of the voids gradually decrease. The oxides are gradually broken into flakes and eventually disappear. The grain boundaries gradually cross the welding interfaces to form new grains, and the welding quality is gradually improved. The ultimate tensile strength (UTS) of the longitudinal welds shows an upward trend, the elongation (EL) first rises and then tends to be stable. Before complete welding, the hardness at the welding interface is lower than those of the areas on both sides of the interface. Based on the results of testing and characterization, the interfacial bonding mechanism of the longitudinal welds in the unsteady zones was revealed. A method for predicting the length of the unsteady zones of profiles extruded by porthole die was proposed, by which the length of the unsteady zone of the aluminum alloy profile used for air-conditioning refrigerator ice box was successfully predicted.

Strain localization at longitudinal weld seams during plastic deformation of Al–Mg–Si–Mn–Cr extrusions: The role of microstructure

The current work was motivated by the increasing use of hollow aluminum extruded profiles for automotive applications and the need for a better understanding of the mechanical response of extrusion seam welds. Two Al–Mg–Si alloys were studied, one without Mn and one with 0.5 wt%Mn and 0.15 wt%Cr. A high temperature homogenization was applied, resulting in a high density of α-Al(Fe,Mn)Si dispersoids in the Mn containing alloy, and an essentially dispersoid free microstructure in the other. The alloys were extruded through a simple porthole die (with two ports) to produce a strip with a centerline weld seam. The Mn free extrudate had a recrystallized grain structure whereas the Mn and Cr containing material was unrecrystallised. There were significant spatial variations of microstructure between the weld seam and surrounding regions, in particular the crystallographic texture. Tensile tests were conducted with the loading direction perpendicular to the weld seam using digital image correlation (DIC) to characterize the local strain distribution. Strain localization and final fracture occurred at weld seam for the unrecrystallized material whereas these occurred away from the weld line in the recrystallized case. The role of local crystallographic texture was examined through polycrystal plasticity simulations using the visco-plastic self consistent code (VPSC). These simulations indicated that the weld seam region was mechanically stronger than the surrounding region for the recrystallized alloy and correspondingly weaker for the unrecrystallized case, thereby rationalizing the experimental results of strain localization and final fracture location.

Workability improvement on Al alloy inhomogeneous blanks by cryogenic forming

ABSTRACT A novel cryogenic forming method is proposed to improve the workability of Al-Cu-Mn alloy friction stir-welded (FSW) blanks in this paper. Experiments were conducted to study the formability, deformation processing, and microstructure evolution of FSW blanks at liquid nitrogen temperatures. The cryogenic tensile properties of the joints showed that the plastic efficiency increased from 70.6% to 91.1%. The longitudinal weld fracture strain increased, and the ultimate tensile strength difference between the weld and base material decreased by 77.5% at −196°C. The cryogenic limiting dome height of the FSW blank increased from 25.4 mm at room temperature to 36.3 mm. The strain inhomogeneity of the bulged part decreased at −196°C. The FSW blank exhibited synergistic enhanced formability and deformation uniformity because of the improved plasticity of the weld zone and the smaller strength differences of the base material zone and weld zone at −196°C. The easy multiple slips in the nugget zone decreased the localized slips and increased the plasticity during cryogenic deformation. The decreased strength differences at cryogenic temperature were attributed to the significant dislocation strengthening of the coarse-grained base material.

Quality Analysis of AISI 321 Welds of Bellow Compensators Used in Shipbuilding

The production of compensators (expansion joints), and especially of bellows as their most demanding elements, requires the usage of stainless materials. These stainless materials exhibit certain particularities at welding (and quality control) since they are very thin, i.e., their thickness ranges usually from 0.12 to 3.00 mm. This paper starts with the elaboration of compensators and their application, and further presents characteristics of the material selected for experimental testing. In the second part, the paper continues with a description of the experiment referring to longitudinal welding of samples without filler material. The experiment focused on the determination of accurate characteristics of radiographic recordings and their assessment based on comparison with the tensile testing (mechanical properties), FEM numerical simulation and dimensional control. The paper also presents the analysis of obtained results and conclusions made thereof. The research hypothesis was to determine in what way the welding parameters affect the mechanical properties, the geometric shape of the welds, and the exploitation possibilities of the compensator. According to the performed experimental part and the performed testing of mechanical properties, all welded joints are acceptable for use. Nevertheless, according to the standard that prescribes the acceptability criteria of defects that occur in welded joints, some of tested samples were not suitable for operating conditions. Such kinds of welded sheets must be repaired or eliminated from further processing.

Numerical investigation of residual stresses in welded joints of cylindrical shell

Welded cylinder structures such as pressure vessels and pipes for transportation have been applied in power stations, aerospace, and shipping industries. The study of weld-induced residual stress is vital in predicting the life of welded cylinder vessels. Depending upon the required diameter and length, they are welded by either circumferential welding or longitudinal welding. In the present work, a sequentially coupled thermal, structural analysis is carried out on circumferential and longitudinal butt weld joints of AH-36 cylinder components. The thermal field distribution and subsequent residual stresses during Gas Tungsten Arc Welding (GTAW) are studied. The moving heat source considered for analysis is based upon Goldak’s double ellipsoidal model. The weld-induced axial and hoop stresses are evaluated on both the outer and inner surfaces of the cylinder. The results for circumferential and longitudinal butt weld joints are compared. The magnitude of peak hoop and axial stresses in longitudinal butt weld joints are 45% and 95% higher than in circumferential butt weld joints. The developed analysis model, used to evaluate the thermal histories and residual stresses, is validated with experimental measurements.

Experimental behavior of circular composite columns with different weld arrangements

Eighteen (18) circular short composite columns including 9 concrete-filled steel columns and 9 concrete-filled stainless steel columns, were experimentally studied in this paper. All composite columns have the same dimensions: D= 160 mm, H= 300 mm and t= 2 mm. The objective of this study is to shed light on the effect of the number and arrangement of lateral and longitudinal welds on the resistance and behavior of concrete-filled composite columns. Based on the results obtained, it was confirmed that weld joints have slight effect on the bearing capacity and instability modes of the studied composite columns. Lateral and longitudinal welds were very successful in conveying compression and bending efforts. The experimentally measured load-bearing capacities of the composite columns were compared to those predicted by Eurocode 4, AISC 360–16 and the equation proposed by Giakoumelis and Lam. All the results predicted by the AISC 360–16 code showed a good concordance with the experimental test results. However, the predictions calculated by the EC4 and the equation proposed by Giakoumelis and Lam were not conservative. This investigation shows that the use of lateral and longitudinal welds in composite columns applications would result in a reliable and economical design. This encourages designers to build their confidence in the use of this type of waste metal plates as structural components of locally produced materials.

Investigating the Residual Stresses During Angular Hard Facing of Mild Steel

In this study, permanent stress and deformations resulting from angular weld seams of the hardfacing process in flat plates were investigated. Temperature distributions, stress distributions, and permanent deformations were calculated in the study carried out with the finite element method. Experiments in the literature were used for validation. A very high agreement was obtained between the experimental and model results. Since only longitudinal and transverse welds were examined in previous studies, how angular welds will affect stress and deformations has been demonstrated in this study. In addition, the changes in stresses were calculated considering the cooling time after the welding process. Among the findings, it has been observed that long weld seams cause higher temperatures, deformations, and stresses. In addition, after cooling, it is seen that the stresses increase even more in terms of both tension and compression.

Evolution mechanisms of charge weld during porthole die extrusion of ZK60 Mg profile

Charge weld greatly affects the rate of material utilization and the mechanical properties of extruded profile. The evolution mechanisms of charge weld during porthole die extrusion of ZK60 Mg alloy were studied in this study. It is revealed that the material flow velocity was a key factor determining the geometric shape and length of charge weld, and the new billet always firstly appeared in the zone with high flow velocity. The die structure and process parameters strongly affected the length of charge weld, relying on the adhesive effect between old billet and die cavity. The dense impurities and oxides distributed on the front of charge weld, and the partial dynamic recrystallization (DRX) took place in new billet zone. With the extension of charge weld, the density of impurities and oxides was reduced and the microstructure was refined. The old billet always owned high DRX degree, and its grain size increased with the extension of charge weld. The fracture of profile followed the order of uniform plastic deformation, strain concentration near charge weld and longitudinal weld, debonding of new and old billets close to charge weld, crack of peripheral old billet near charge weld, and complete fracture. In addition, the profile with charge weld experienced two-time stress drops during the tests due to the debonding of charge weld and the crack of peripheral old billet. The mechanical properties were deteriorated by the emergence of charge weld, while they were gradually improved with further evolution of charge weld.

Effects of welding angle on microstructure and mechanical properties of longitudinal weld in 6063 aluminum alloy extrusion profiles

In order to explore the effects of welding angle on microstructure and mechanical properties of longitudinal weld, a porthole die with different welding angles was designed and manufactured, by using which various extrusion experiments were carried out. The microstructure and mechanical properties of longitudinal weld were characterized, and the extrusion process was simulated. The results show that as welding angle increases, the longitudinal weld gradually transforms from a linear shape to a cross shape. A larger welding angle will not only reduce stress triaxiality and strain rate in the main welding zone, but also increase area of the dead metal zone, thus leading to poor welding quality. The crystal orientations of <100> and <111>//ED can be found in the welding zones of the profiles extruded by using the dies with different welding angles, and the texture components exhibit significant differences. There are a certain number of dislocations, a small amount of Mg2Si precipitates and insoluble iron-containing intermetallic compounds in the welding zones. By comprehensively considering the influence of welding angle on welding quality, extrusion load, effective stress and strain of the porthole die, the welding angle ranges under different welding quality requirements were determined. It is found that the welding quality is higher when the range of welding angle is 38–46°, the welding quality is lower when the range of welding angle is 54–68°. If taking in account both of welding quality and porthole die strength requirement, the preferred welding angle is recommended to be in the range of 46–54°.

Review of European design provisions for buckling of aluminium members with longitudinal welds – part 1

Review of European design provisions for buckling of aluminium members with longitudinal welds – part 1

Overview on the fatigue strength of single-sided transverse and longitudinal fillet weld joints

In the present study, an overview on the fatigue performance of single-sided fillet welds is carried out. Both longitudinal load-carrying joints, for instance existing in beam structures and welded hollow sections, and transverse joints are considered in this work. Experimental data of such joints made of mild and ultra-high-strength steel (UHSS) is extracted from existing studies to evaluate the fatigue strength properties. The main characteristics affecting fatigue strength properties of these joints are discussed. Furthermore, the paper evaluates the fatigue strength of single-sided fillet weld joints in comparison with the joints with double-sided welds. The experimental results indicate that in the transverse welds, an increase in material’s yield strength shows a slight decrease in fatigue strength compared to mild steels, while in the longitudinal load-carrying seams, in the case of continuous weld root geometry, high fatigue strength can be achieved with UHSS materials. The double-sided welds provide one FAT class higher fatigue strength for transverse non-load-carrying joints, obtained in terms of mean fatigue strengths. In addition, in transverse joint configurations, intermediate welding was found to have no detrimental effect on the fatigue performance compared to the joints with continuous welds. In longitudinal load-carrying joints, double-sided welds do not provide any additional benefit unless full penetration and, thus, continuous longitudinal weld root shape is achieved with such weld preparation.

Strain Localization at Longitudinal Weld Seams During Plastic Deformation of Al-Mg-Si-Mn-Cr Extrusions: The Role of Microstructure

Strain Localization at Longitudinal Weld Seams During Plastic Deformation of Al-Mg-Si-Mn-Cr Extrusions: The Role of Microstructure

Prediction of residual stresses in high-strength S690 cold-formed square hollow sections using integrated numerical simulations

In general, residual stresses are induced in structural members during various fabrication processes, such as welding, bending, press-braking, folding, flame cutting and punching. The presence of those residual stresses in cold-formed square hollow sections (CFSHS) primarily caused by i) transverse bending (or cold-forming), and ii) longitudinal welding, is widely considered to have modified both initial stress and strain conditions of these steel members significantly. Hence, these residual stresses are widely considered to have significant adverse effects onto the structural performance of these CFSHS under various actions.In order to examine and quantify both magnitudes and distributions of these residual stresses in S690 CFSHS, an investigation is undertaken to measure residual stresses due to transverse bending and longitudinal welding. Moreover, an approach of integrated numerical simulations is adopted in which a total of three co-ordinated finite element models are established together with various element types and block data transfers to generate compatible meshes for the following three analyses: i) two-dimensional plane-strain bending analyses with large plastic deformations and springback, ii) three-dimensional heat transfer analyses for transient temperature distributions under a heat source, and iii) three-dimensional thermomechanical analyses for welding-induced residual stresses.The predicted results of these three analyses have been carefully calibrated against various experimental data, such as surface temperatures during welding, and residual stresses and strains after welding. Good comparisons between the measured and the predicted data of these S690 CFSHS are demonstrated. The complete residual stress distributions within typical S690 CFSHS due to transverse bending and longitudinal welding are illustrated in three-dimensional plots while simplified residual stress patterns of these sections with specific values and parameters are also provided for subsequent advanced structural analyses and design.The proposed modelling technique for transverse bending and longitudinal welding with compatible meshes of two-dimensional and three-dimensional models with various element types and block data transfers is demonstrated to be highly effective. The technique is readily applicable to simulate residual stresses of all fabricated sections manufactured with transverse bending and longitudinal welding, and, thus, the simulated residual stresses can be employed in subsequent structural analyses of all fabricated members.

Estimation of Arc Welding Pressure Pipeline Weld Peaking Parameters Based on Data Prediction

Peaking parameter is the key content in the regular inspection of the pressure pipeline. Solving the problem of the peaking measurement method defined by a standard cannot be applied to a situation in which there exists a weld surface with reinforcement and misalignment. In this paper, a peaking estimation method based on data prediction was proposed to estimate the contour information of the base metal at the weld joint using the contour point set data of the base metal part of the weld. Herein, the longitudinal weld peaking estimation method based on a piecewise logistic regression (PLR) and the girth weld peaking estimation method based on a piecewise Bayesian linear regression (PBLR) were studied, and the midpoint of the two symmetrical points of the base metal on either side of the weld was used as a reference for calculating the peaking. Finally, we collected the surface profile data of longitudinal weld pressure pipes with diameters of 155 mm, 255 mm, 550 mm, and 600 mm and the surface profile data of girth weld pressure pipes with diameters of 120 mm, 130 mm, 140 mm, and 170 mm. This weld seam data used the data estimation method proposed in this article and traditional long short-term memory and fitting methods. The results showed that the proposed data prediction method could accurately predict the position of the base metal, and the theoretical mean absolute error of the peaking estimation based on the PBLR and PLR could attain 0.06 mm and 0.07 mm, respectively, which meets the parameter measurement requirements of related verification fields.

Fatigue strength of hot-dip galvanized S960 cut edges and longitudinal welds

Experimental fatigue test series were conducted for component sized hot-dip galvanized (HDG) S960 cut edges and longitudinal welds. Scanning electron microscopy (SEM) was used to identify and characterize the crack initiation location and the effects of local chemical composition. Micro-scale liquid metal embrittlement in the vicinity of the cut surface was found to slightly reduce fatigue performance of tested laser cut, machined and welded specimens. The use of ultra-high-strength steels in the HDG condition is discussed and fatigue strength guidelines are proposed for the tested details.

Connections of Steel Girders with End Plates and Partially Prestressed Bolts

Abstract The connections with end plates and bolts can be used in steel bridge structures, or joining the decking beams, which can lead to very simple and economical constructive solutions. The paper presents some theoretical aspects concerning the behavior and calculation of the end plate connections which is partially pre-tensioned by high-strength bolts, and supplementary a welded cover plate is added to the tensioned flange of the plate girder. In the case of connections subjected to tension forces, it is not recommended to prestress the bolts as much as is the case when the joints are subjected only to shear because live loads can lead to the overloading of the bolts; the overload is a function of the relative stiffness of the end plate and of the bolts. The additional welded splice at the tension flange contributes to the transfer of the large tension stresses from the extreme bolts to the welded cover plate, resulting in a significantly reduced joint assembly loading and an increased load-bearing capacity. The paper includes a numerical example highlighting the influence of the stiffness of the joint elements and of the welded splice-plate on the joint loading, considering its pre-tensioning effect from the cooling contraction of the longitudinal welding fillets.

Residual shearing strength of fillet weld connections after exposure to elevated temperature

Experimental and analytical studies are carried out to investigate the residual shearing strength of fillet welded connections after exposure to elevated temperatures. Transverse fillet welds and longitudinal fillet welds were designed in the test, and four weld leg heights were considered. Fourteen specimens were manufactured for each weld leg height, including seven heating temperatures and two cooling methods, obtaining a total of 112 specimens, along with 8 unheated specimens for comparison. The load-displacement curves and stress-load ratio curves were obtained to evaluate the shearing strength, residual deformation, stress development, stiffness and ductility of the fillet welds. Test results exhibit the transverse fillet welds are mainly integral fracture, while longitudinal fillet welds occur obvious local and global cracks. The weld leg height has the greatest influence on the shearing resistance of fillet welds, followed by the elevated temperature and cooling method. When the heating temperature is between 400 °C-600 °C, an increasement in residual shearing strength can be noticed. Meanwhile, the residual deformation is positively correlated with the weld leg height. Additionally, water-cooling fillet welds are superior to room-temperature-cooled fillet welds in terms of stiffness and ductility. Moreover, the formulae for predicting the residual shearing strength of the fillet welds after exposure to elevated temperatures are proposed.