T-welded Joints Research Articles

Damage detection in the T-welded joint using Rayleigh-like feature guided wave

Steel T-welded joint structures have been largely applied in aerospace and marine infrastructures. The weld length in T-weld joint structures is usually long, and it is difficult to access the weld conditions for damage detection purposes. This is due to the T-welded joint structure possessing a more complex cross-section than the conventional welded plate-like structures. Rather than formed by two plates and joined with a butt weld, the joint regions in the T-welded joint structure are connected to the sides of three plates to form a T-welded joint, and hence cannot be considered as plate-like structures. This makes guided wave modes difficult to be identified and exploited. This paper assesses the feasibility to detect weld defects on a steel T-welded joint structure using the feature guided wave (FGW) technique. FGW technique can provide a fast and long-range inspection for local topographical features, such as welded joints, offering great potential for effective screening of damages. Semi-Analytical Finite Element (SAFE) method is applied to acquire modal solutions in the waveguide. A new algorithm is developed to obtain FGW modes with both high energy concentration and low attenuation from the solutions of SAFE eigenvalue problem. One particular FGW mode with similar mode shape as the Rayleigh surface wave is identified, of which the propagation occurs only in the joint region with small attenuation. This FGW, labelled Rayleigh T-welded wave (RTW), is explored in comprehensive experimental and numerical studies to investigate the propagation and backward scattering characteristics regarding optimal excitation frequency and different sizes of weld defect. The numerical and experimental results are in good agreement. The outcome of the study confirms the capability and robustness of RTW in detecting small weld defects, which allows a long-distance and sensitive screening for the small weld defects at the joint region in the T-welded joint structure.

Fatigue properties evaluation of fillet weld joints in full-scale steel marine structures

This study investigated the fatigue behavior of fillet weld steel joints (including cruciform and T-welded joints) in marine structures based on experimental tests and finite element analysis (FEA). In cyclic tensile loading, fatigue failure of full-scale specimens consistent with in-plane failure mode of marine structures was validated with ultrasonic phased array testing (UPAT). The effect of incomplete penetration and weld profile on fatigue performance were analyzed based on traction structural stress method. The results showed that the failure mode of load-carrying cruciform joints would change when the incomplete penetration ratio p’/tr reached 0.91. And the concave weld profile is better choice for welded structures anti-fatigue design. In view of the complexity of fatigue performance evaluation of fillet weld joints in IIW and BS7608 standards, a unified master S–N curve covering different plate thicknesses, materials, and weld profiles was proposed.

Determination of the three-dimensional welding residual stress in a thick plate T-welded joint using the stepwise eigenstrain-contour method

The stepwise eigenstrain-contour method (SECM) for determining three-dimensional welding residual stress (WRS) was developed based on conventional eigenstrain-contour method. A thick plate T-welded joint specimen was manufactured and its three-dimensional WRS was measured via the SECM. The SECM was then verified by the superposition method, which obtains the three-dimensional WRS on the cut surface by superposing the measurement results of the hole-drilling method and the standard contour method. Finally, the three-dimensional eigenstrain field and WRS field in the thick plate T-welded joint specimen were comprehensively analyzed. The results show that the SECM greatly improves the reconstruction accuracy of the WRS components in non-principal directions of the welded joint, thus extending the standard contour method to three-dimensional WRS measurement. Overall, the three-dimensional WRS in the specimen presents self-equilibrated tension-compression distribution. The peak longitudinal, transverse and vertical WRSs on the whole mid-length section of the specimen are 382.3 MPa (0.92 σy), 152.7 MPa (0.37 σy) and 105.8 MPa (0.26 σy) respectively, which usually appear near the bottom of weld zone. The transverse and vertical WRSs are usually smaller than the longitudinal WRS, and the WRS in the flange is generally greater than that in the web.

Control of Welding Residual Stress in Large Storage Tank by Finite Element Method

T-joint welding is a key manufacturing process of large storage tanks. However, complex residual stresses are generated and have a great effect on the structural integrity of storage tanks. The high residual stress caused by welding and the discontinuous structure may result in tank cracking and failure. In this work, the residual stress distributions on the inner surface, outer surface, and thickness direction of the T-joint were investigated by using the finite element method and indentation test method. The effect of local PWHT with different heating temperatures, heating rates, and heating widths on the residual stress distribution was also discussed. Results show that the residual stress of the T-shaped joint is high due to the serious structure discontinuity, multi-layer welding, and high strength. Among all the stresses, the circumferential residual stress is the highest and most concentrated in the outer weld connected with the annular plate. The residual stress gradually decreases with the increase in the heat treatment temperature. When the heating rate is less than 106 °C/h, the residual stress gradually decreases with the decrease in the heating rate. The large thermal deformation caused by heat treatment can be simultaneously avoided by heating the inside and outside of the T-joint. The residual stress decreases with the decrease in the width of the heating zone. The residual stress can be regulated by using a smaller width in the heating zone. An optimized heat treatment scheme with a heating temperature of 700 °C, heating rate of 56 °C/h, and heating width of 200 mm was proposed, which has a good ability to control residual stresses and improve the quality of the T-joint. It also has a good application in engineering.

Numerical Simulation of Droplet Filling Mode on Molten Pool and Keyhole during Double-Sided Laser Beam Welding of T-Joints

The effects of droplets filling the molten pools during the double-sided laser beam welding (DSLBW) of T-joints was established. The dynamic behavior of the keyhole and the molten pool under different droplet filling modes were analyzed. The results indicated that compared with the contact transition, the stability of metal flow on the keyhole wall was reduced by free transition and slight contact transition. At the later stage of the droplet entering the molten pool via free transition, slight contact transition, and contact transition, the maximum flow velocity of the keyhole wall was 5.33 m/s, 4.57 m/s, and 2.99 m/s, respectively. When the filling mode was free transition or slight contact transition, the keyhole collapsed at the later stage of the droplet entering the molten pool. However, when the filling mode was contact transition, the middle-upper part of the interconnected keyholes became thinner at the later stage of the droplet entering the molten pool. At the later stage of the droplet entering the molten pool via free transition, the flow vortex at the bottom of the keyhole disappeared and the melt at the bottom of the keyhole flowed to the rear of the molten pool, however, the vortex remained during slight contact transition and contact transition.

Residual stress and material flow prediction in Friction Stir Welding of Gr2 Titanium T-joints

Friction Stir Welding is nowadays an established technique successfully used by many industries. However, most of the research and, consequently, most of the applications regard aluminum alloys and butt joints. T-joints are of high interest for different industrial sectors as aeronautical, aerospace, naval and ground transportation, for which joint integrity and low residual stress are extremely important. In this study, an experimental and numerical approach is proposed with the aim to study the peculiarities of the residual stress distribution and material flow occurring in FSW of CP-Ti T-joints. Experiments were carried out to assess the feasibility of the process and to acquire the temperature data needed for the validation of a specifically set-up numerical model. Peculiar numerical strategies have been defined in order to calculate the residual stress with affordable CPU time and to highlight the bonding surface between the skin and the stringer. Main findings include a longitudinal residual stress profile different from the one usually found for butt joints. The reasons for this behavior were explained through a deep investigation on the temperature distribution in space and evolution in time. Finally, the bonding surface between skin and stringer was highlighted together with the possibility of flow defects in the fillet area.

Simultaneous Double-Sided Metal Inert Gas Welding of AA5052 Aluminum Alloy T-Joints

Simultaneous double-sided MIG welding as alternative method for joining the skin-stringer T-joints were investigated. The microstructure and mechanical properties of the welded joints were examined. Our study showed that a distance of 27-mm (torch to surface) results in the best weld appearance. Shorter distance produces higher heat input and causes the material stringers to melted with the filler, while longer distance increases the number of porosity and prevents the formation of a complete fusion zone.

A Study on Welding Characteristics, Mechanical Properties, and Penetration Depth of T-Joint Thin-Walled Parts for Different TIG Welding Currents: FE Simulation and Experimental Analysis

Considering the effect of heat input of tungsten inert gas (TIG) arc welding for T-joint welding of thin-walled parts of aluminum alloy 6061-T6, here, the welding characteristics are analyzed via the finite element method. The experiments are carried out using scanning electron microscope (SEM), optical microscope (OM), and tensile test of specimens to investigate the microstructure variation of the weld zone (WZ), heat-affected zone (HAZ), and base metal (BM), and the mechanical properties of the T-welded joint. The mechanical properties of the T-welded joint are explored and assessed combined with the tensile test in terms of yield strength, tensile strength, and Vickers hardness. Furthermore, the effects of different welding currents on welding penetration variation under welding deformation are thoroughly investigated, and the appearance of porosity and incomplete fusion defects of T-welded joints are clearly illustrated. The results show that the yield and tensile strength of T-welded joints, respectively, account for less than 37% and 74% of the base metal (BM) strength. Moreover, the welding penetration depth and microstructure of T-welded joints are deeply affected by the welding current. The maximum penetration depth is achieved at about 2.18 mm under the maximum welding current, and partial welding defects emerged, affecting and reducing the mechanical properties of the welded joint. It is expected that these results will provide an analysis foundation for optimization of the welding process, suppression of welding defects, and promotion of mechanical properties for thin-walled parts in the future.

An improved crack growth model of corrosion fatigue for steel in artificial seawater

Corrosion will greatly reduce the fatigue life of steel structures. Based on the Paris equation and continuum damage mechanics, an improved crack growth model is obtained by introducing corrosion damage into the Paris equation. The derivation and calculation procedure of the improved Paris equation are discussed in detail. The proposed model was used to calculate the corrosion fatigue crack growth length of S690 in 3.5 wt% NaCl solution. The model demonstrates good accuracy and predicts the corrosion fatigue life of T-welded joint specimens in artificial seawater.

Investigation of welding parameters effects on temperature field and structure field during laser-arc hybrid welding

Thermo-structural weak coupling model was adopted in numerical simulation of laser-arc hybrid T-joint welding. Gauss surface heat source and Rotary-Gauss body heat source were used to form a combined heat source in the temperature field analysis and simulate the arc and laser heat source. The laser-arc hybrid overlaying welding test of 304 stainless steel was carried out, and the weld molten pool morphology was obtained by metallographic corrosion test. The test results of a molten pool morphology show that the combination heat source can better simulate the laser-arc hybrid welding process. The effects of laser power, arc power and welding speed on residual stress and deformation of T-joint in laser-arc hybrid welding were studied by orthogonal experiments. Experimental results show that the arc power has great influence on the depth-width ratio, the laser power has great influence on the welding residual stress, and the welding speed has great influence on the thermal deformation. Through quantitative analysis and comparison, the optimal parameters were found during laser-arc hybrid welding.

Finite Element Simulation and Experimental Validation of Welding Distortion of Fillet Welded T-joints

This research presents a numerical simulation for predicting welding induced distortion with an experimental validation. Three experimental specimens of S355J2G3 structural steel with thicknesses of 3mm, 5mm and 8mm have been used as test cases. In order to validate the results an experiment was set up to gain detailed information about distortions occurring in single fillet welded T-joints. The non-linear heat transfer analysis is used and heat source is modeled with the Goldak’s double ellipsoidal distribution by using SYSWELD in the gas metal arc welding (GMAW) process. This study employs the finite element (FE) method to evaluate residual stresses and angular distortions. A series of FE simulations and corresponding experiments are performed to evaluate the depth of penetration in the cross sections, angular distortions that occur after welding, temperature distribution, and residual stresses. A coordinate measuring machine and a 3D non-contact scanning device are used to measure the angular distortions and displacement distributions, respectively. The results show that controlling welding process via simulations can significantly enhance the performance of process, and help to minimize distortions and decrease costly design errors.

Numerical investigation of weld bead porosity reduction in the oscillating laser T-joint welding of aluminum alloy

T-joint welding is widely used in the assembly process of automotive, aerospace, and other industries. The pore defect is easily formed in the weld bead during the laser T-joint welding of aluminum alloy. In this paper, a three-dimensional numerical model of the oscillating laser T-joint welding of aluminum alloy with presetting solder patch is established to reduce pores in the weld. Both the molten pool dynamic behaviors in the oscillating laser T-joint welding and non-oscillating laser T-joint welding are analyzed by the numerical simulation results. It is found that the porosity of weld bead can be reduced by the dynamic behaviors in the oscillating laser welding. The reduction process of porosity in the oscillating laser T-joint welding of aluminum alloy is discussed in detail. The numerical calculation results are compared with that of the experiments and good agreement between them is found. Therefore, the proposed method is of great importance for reducing the weld bead porosity in laser welding of aluminum alloy and achieving the high quality welding process.

Simulation of crack growth in residual stress fields of pre-fatigued T-welded joints repaired by tungsten inert gas: a 3D approach

In this article, a three-dimensional finite element model (FEM) is used to predict the crack growth at the weld toe of a pre-fatigued T-joint that was repaired with a remelting technique. The numerical models were developed using the MSC.Marc software. Fatigue life is estimated by integrating the Paris-Erdogan law. The stress intensity factors are obtained by the virtual crack closure technique (VCCT).The T-welded joints, made of S355 steel, are obtained by covered electrode process and pre-cracked by fatigue. These welded joints were repaired by TIG dressing. The stress field generated by this dressing technique was estimated using a FEM model, presented in authors’ previous works. For the crack growth was used the VCCT three-dimensional model recently presented by the authors to predict the effect of overloads. The pre-existence of an elliptical crack at the weld toe, with a depth of 0.5 mm was considered. It is also studied the growth of pre-existing cracks which have been poorly repaired.It was observed that the TIG dressing produce residual compression stress fields on the weld toe that causes a delay in crack growth. The obtained results are compared with experimental ones. The fatigue’s lives obtained by simulations with the numerical model presented in this paper allows to evaluate the application conditions of TIG remelting technique in the repair of pre-cracked welded joints.

Opportunities and partial problems of HFMI implementation in design of welded structures of rail vehicles

This paper highlights the main impacts of HFMI (High Frequency Mechanical Impact) technology on increasing the fatigue resistance and extending the fatigue life of welded joints. In the case study there are SN curves of T-welded joints made of two different steels (conventional steel S235JR and high strength steel S460MC). For both materials there is a comparison of SN curves with and without HFMI treatment. Both samples are loaded by bending for cycle asymmetry R = 0. The failure criterion is a decrease in stiffness caused by the formation of a macrocrack. The results of fatigue testing are then applied in a parametric study, which assumes a random loading of a selected structural detail in a railway application. Opportunities and barriers of the implementation of HFMI in practice are mentioned and documented according to results of laboratory experiments, which take place in cooperation with the university research center and the manufacturer of railway vehicles.

Improvement of Fatigue Life of Arc Welded T-joints by Local Shape Change Near the Joint Line

ABSTRACT: The objective of this study is to improve fatigue life of T-shape arc welded joint structures which are often used in automobiles. In conventional T-shape joint, ST-joint (Standard T-joint), a vertical part is welded to a flat surface in the horizontal part. In this paper, a new structure, CCT-joint (Concave shape T-joint), is proposed which can reduce stresses around a joint line in car driving. In a CCT-joint, a vertical part is welded to a concave surface in the horizontal part. Fatigue life of a CCT-joint was significantly longer than that of a conventional ST-joint. Results of this study suggest that the drastic improvement in fatigue life was due to stress reduction by the concave shape around the joint line. FEM stress analysis revealed that the maximum stress near the weld line of CCT-joint was reduced to less than half that of the ST-joint. Furthermore, it was found that the locations of the maximum stress were different between the CCT-joint and the ST-joint. This suggests that the crack origin positions of both joints are different, which was also confirmed experimentally. The geometry, hardness, and residual stresses after welding were investigated around the weld toe. The effects of geometry and hardness were small on the fatigue life. The residual stresses were decreased by CCT-joint. The evaluation of the advantage of residual stress reduction by CCT-joint compared with that of stress reduction in car driving will be investigated and discussed in the next step of this study.

Experiment on different T-joint characteristics for laser-welded I-core galvanized steel sandwich plates

The sandwich plate is one of the lightweight structures that have been utilized in lightweight applications. One of the topologies, such as I-core, was designed to evaluate the mechanical behavior when subjected to 3-point bending test. A theoretical formula for an I-core sandwich plates was discussed on the bending stiffness. In this project, galvanized steel elements (faceplate and core) were fabricated through welding. The manufacturing process for both galvanised steel and PVC foam was mentioned in detail, and the laser weld geometry parameters were summarized. Significantly, T-joint were made into different weld dimension characteristic. Hence, special equipment was used to assemble the elements. Overall, the study shows a positive outcome. It can be seen that with and without rootgap divide the centric and eccentric characteristic curve. The sequence from higher to lower stiffness is as follows: centric + no rootgap > eccentric + no rootgap > centric + rootgap > eccentric + rootgap. An ideal characteristic generates higher stiffness than other failures by inserting PVC foam: for instance, eccentric + no rootgap presented 5.2% difference from ideal. Furthermore, faceplate failure mode is a noticeable deformation displayed during the experiment, such as face wrinkling and face yielding. Meanwhile, debonding is also a notable failure mode, demonstrated at the T-joint and PVC foam. Therefore, this study provides a useful understanding of strength and stiffness via different T-joint weld dimension characteristics and failure mode of I-core sandwich plates.

Study on Medium-Thick Al-Alloy T-Joints by Dual P-GMAW Bilateral Synchronous Welding

The T-joints of medium-thick 6082 Al-alloy plates created by dual pulsed gas metal arc welding (P-GMAW) and bilateral synchronous welding were investigated to improve weld quality using the adaptive deposition method, which calculates the minimum amount of deposition according to the welding condition, groove size, and cross-sectional area, effectively reducing the heat input and deformation of the welds on the basis of weld filling. The optimized linear energy with a wire feed speed (WFS) of 9.5 m/min can ensure a well-formed weld with a complete root fusion, and high-quality T-joint welds were obtained both in root openings of 0 mm and 1 mm. The biggest penetration was 4 mm, which was four times more than that of the result from a single torch welding process. When the distance between the two welding torches exceeded 20 mm, the molten pool was completely separated, and process pores were observed in the unfused root zone. Influenced by the thermal cycles in asymmetric welding, the hardness distribution changed: the width of the softer zone at the base plate with the fore arc was smaller than that zone with the rear arc. Furthermore, dual P-GMAW bilateral synchronous welding with an asymmetric heat source can further reduce the deformation of the welded joint by about 20% compared to that of symmetric welding.

Molten Pool Behaviors in Double-Sided Pulsed GMAW of T-Joint: A Numerical Study

The T-joint is one of the essential types of joints in aluminum welded structures. Double-sided welding is a preferable solution to maintain high efficiency and avoid significant distortion during T-joint welding. However, interactions between double-sided molten pools make flow behaviors complicated during welding. Numerical simulations regarding molten pool behaviors were conducted in this research to understand the complex flow phenomenon. The influences of wire feed rates and torch distances were simulated and discussed. The results show that droplet impinging drives the fluid to flow down to the root and form a frontward vortex. Marangoni stress forces the fluid to form an outward vortex near the molten pool boundary and flatten the concave-shaped molten pool surface. With an increased wire feed speed, the volume of the molten pool increases, and the root fusion is improved. With an increased torch distance, the width of the front molten pool decreases while the length increases, and the rear molten pool size decreases slightly. Both wire feed speeds and the torch distances have limited influences on the basic flow characteristics.

Multiobjective Genetic Algorithm applied to inverse finite element analysis: T-joint welding case study

ABSTRACT Welding processes play as an important role in the manufacturing of a lot of products in most of industrial sectors. Despite its wide applicability, the welding process is subjected to some inconsistencies in quality due to controllable and uncontrollable variables. This work is aimed to use inverse Finite Element Analysis (FEA) to simulate the movement of the heat flow in the base metal submitted to the Gas Metal Arc Welding (GMAW) process. To this end, control limits were established, such as voltage and electric current (in the form of the heat source) and welding speed in order to obtain optimized values of deformations and stresses along the plates subjected to the GMAW welding process. For the numerical simulation process modelling, empirical data from weld beads applied on both sides of two ASTM A36 steel plates (thickness of 9.5 mm each) were used in a T-joint configuration. In this case, a multiobjective algorithm to find the optimized solution was used. Non-dominated Sorting Genetic Algorithm II (NSGA II) in conjunction with FEA was applied. The results presented are consistent with literature data within the pre-established limits, which are deformations and stresses less than 2 mm and 600 MPa, respectively. This demonstrates the potential of using FEA in conjunction with the NSGA II genetic algorithm to predict input variables in welding processes. This can be considered an important contribution to the industrial technological advancement for predicting welding process’s variables.

An improved life prediction model of corrosion fatigue for T-welded joint

Fatigue and corrosion fatigue tests were conducted for T-welded joint specimens. The test results show that the corrosive environment greatly reduces the fatigue life of the specimens. The average reduction percentage under different stress ranges Δσ were 47.7% (Δσ=172.5MPa), 58% (Δσ=216MPa) and 45.7% (Δσ=258MPa) respectively. Based on Continuum Damage Mechanics (CDM), a corrosion fatigue life prediction model considering the coupling effects of corrosion environment and cyclic load was proposed. This prediction model can predict the corrosion fatigue life of present T-welded joint specimens and other specimens reported in previous researches, showing rationality and versatility.