T-joint Configuration Research Articles

Autogenous double-sided T-joint welding on aluminum alloys using low power fiber laser

In this study, a successive double sided laser beam welding process was used to join dissimilar aluminum alloys, AA2024-O and AA7075-T6 using a low power Yb-fiber laser in a T-joint configuration without additions of filler materials. The influence of welding speeds and focal distances were evaluated. First, the welding speeds were varied from 12 mm/s to 21 mm/s at a constant laser power of 270W. Optical microscopic observations have shown that the minimum gap line of 0.8mm was obtained at a laser welding speed of 12mm/s, while the maximum gap line of 1.8mm was obtained at a laser welding speed of 21mm/s. The focal distance with offsets of -1, 0 and +1 at welding speed 18mm/s were evaluated, showing variations in the gap line. Vickers microhardness evaluation across the welding region showed the hardness values at the fusion and heat affected zones were lower than those of the base metals when welding speed varied. Meanwhile, the Vickers microhardness increases when focal distance is defocused +1. The pull test showed the force needed to fracture the welded specimens increased from 101N to 427N as the welding speed decreased from 21mm/s to 12mm/s. For constant welding speed and laser power, the fracture force increased from 100N to 400N as the focal distance changes from -1 to +1. It was observed that a lower welding speed and positive offset value of focal distance will result in deeper penetration, leading to better weld quality between alloys AA2xxx and AA7xxx.

Feasibility Study of Low Power Fiber Laser Welding AA2024 and AA7075 Alloys T-Joint

Dissimilar aluminum alloys, AA2024-0 and AA7075-T6 were laser welded on both sides in a T-joint configuration using a low power fiber laser. The effect of welding speed (9, 12, 15, 18 and 21 mm/s) on weldability was evaluated at laser power of 270W with argon gas as the shielding gas. The sample welding angle was fixed at 45° with an interval of 180 seconds between each welding pass. Macrograph observations revealed that full penetration with pore free weld of these dissimilar joint was obtained at the laser parameters of 270 W and 9 mm/s, suggesting that lower welding speed is preferred during low power laser welding.

Influence of the Overlapping Factor and Welding Speed on T-Joint Welding of Ti6Al4V and Inconel 600 Using Low-Power Fiber Laser

Double-sided laser beam welding of skin-stringer joints is an established method for many applications. However, in certain cases with limited accessibility, single-sided laser beam joining is considered. In the present study, single-sided welding of titanium alloy Ti6Al4V and nickel-based alloy Inconel 600 in a T-joint configuration was carried out using continuous-wave (CW), low-power Ytterbium (Yb)-fiber laser. The influence of the overlapping factor and welding speed of the laser beam on weld morphology and properties was investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. XRD analysis revealed the presence of intermetallic layers containing NiTi and NiTi2 at the skin-stringer joint. The strength of the joints was evaluated using pull testing, while the hardness of the joints was analyzed using Vickers hardness measurement at the base metal (BM), fusion zone (FZ) and heat-affected zone (HAZ). The results showed that the highest force needed to break the samples apart was approximately 150 N at a laser welding power of 250 W, welding speed of 40 mm/s and overlapping factor of 50%. During low-power single-sided laser welding, the properties of the T-joints were affected by the overlapping factor and laser welding speed.

Laser beam welded joints of dissimilar heat treatable aluminium alloys

A serious number of critical aspects have to be considered when aluminium and its alloys, especially if heat treated, are welded. These drawbacks, to date, limit the application of the welded joints in the aeronautical sector. The possibility of overcoming these limitations is focused in current paper by studying the mechanical performance of two types of dissimilar laser beam welds in T-joint configuration. The dissimilar joints, planned for aeronautical applications, combine the same skin, made of AA 6156 alloy, with two different base materials for the stringers, namely the AA 2139 and the non-standard alloy PA765. The alloys under investigation are characterized by enhanced weldability if compared to the standard AA 2024, widely used in aeronautic. Due to the contemporary presence of dissimilar heat treatable aluminium alloys, both joints have been subjected to dedicated multi-step heat treatments.Metallurgical and microstructural analysis were carried out in order to highlight the influence of both chemical composition and thermal cycles experienced on the final microstructures of different zones of the joints, governing the mechanical properties of the joint itself.Vickers micro-hardness measurements were performed to fully characterize the heterogeneity in mechanical properties across the different zones of the dissimilar welds. Strain data acquisition by Digital Image Correlation (DIC) allowed to assess the influence of local weld properties on joints strength in tensile loading. The important role of the temper conditions of the parent materials, resulting from the different joint pre and post-welding heat treatment options, on the tensile behaviour of the skin and, in this way, on the global strength of the connection was showed. The dramatic role played by the Heat Affected Zone and the influence of the distribution of the strengthening elements on examined joints mechanical properties has been put in evidence, according to mechanical test results.

Ultrasonic high-frequency guided waves for the inspection of shell weld in core support structure of fast breeder reactors

This article reports an ultrasonic high-frequency guided wave based methodology for inspection of shell weld of core support structure of the main vessel in 500-MWe sodium-cooled prototype fast breeder reactor. The high-frequency guided waves are generated in 30-mm-thick plate of core support structure at 2 MHz (frequency–thickness product of ∼60 MHz-mm). These wave modes are fairly nondispersive over considerable distance of propagation through the material. In order to understand the generation and propagation characteristics of these high-frequency guided waves, a series of two-dimensional plane strain finite element models are developed using explicit scheme. The optimum transducer placement for generating efficient high-frequency guided wave is achieved by sweeping the transducer position along the curvature of the main vessel plate with respect to the centerline of the vertical shell support plate. The generated high-frequency guided waves are analyzed and identified with the help of dispersion curves and time–frequency analysis. The simulation results are found to capture the features observed in the experimental measurements rather well, and the time of flight of the reflected waves in the simulation is found to be in excellent agreement with the experimental results. The optimum transducer locations for inspection of a general T-joint configuration with different angles between the web and the base have been studied in detail using finite element simulations. With optimum transducer position, the high-frequency guided waves are also used to inspect the artificially introduced defects in the connecting weld of shell support plate. It has been demonstrated that the high-frequency guided wave could detect defects of 20% wall thickness (6 mm) in the connecting shell weld.

Experimental and numerical investigation into effect of weld configuration geometry on distribution of residual stress and temperature in the welded parts of stainless steel

In multi-pass grooved welding, residual stress and corresponding distortion are highly affected by welding process parameters, material properties, and fixture design. Therefore, having knowledge about value of the residual stress and transient temperature yields long life joints with high dimensional accuracy. In the present study, three joints with different T-joint configurations made of 316 stainless steel were fabricated through gas tungsten arc welding process. The first configuration includes single bevel without root face and gap, the second includes single bevel with root face and 1 mm gap, and the third includes double bevels with root face and 1 mm gap. In order to evaluate temperature and residual stress distribution, finite element simulation of aforementioned process using SIMUFACT WELDING software along with hole-drilling method (as semi-destructive evaluation) and ultrasonic method (as non-destructive evaluation) were performed. Also, thermal history of welding process was recorded by K-type thermocouple. Research findings showed that the thermal history and residual stress distribution which were obtained through FE simulation are in high agreement with those derived from both ultrasonic and hole-drilling methods. Furthermore, the change in joint configuration significantly affects transverse residual stress but it has not great impact on longitudinal residual stress. Also, the highest and lowest residual stress and corresponding distortion are for the first and third configurations, respectively.

Evaluation of Adhesive T-Joint Using Finite Element Analysis

This study evaluates the effect of temperature upon adhesive properties and behavior of adhesively bonded T-joint. Finite element analyses established the effect of this parameter on the durability joint and stress distribution within the adhesive layer. A series of temperatures and stress analyses using finite element analysis (FEA) has been conducted in the T-joint configuration for this purpose. The parametric studies on the FE model revealed that stress distributions are sensitive to the changes in adhesive properties due to changes in temperature. In general, stresses were reduced with changes in the temperature which resulted in the ability of the adhesive layer to undergo plastic deformation.

Effect of welding parameters and the heat input on weld bead profile of laser welded T-joint in structural steel

The high power fiber laser has become one of the most efficient energy sources for deep penetration welding processes used in heavy manufacturing and marine industries. Combinations of cost-efficient, easily automatable process together with fairly mobile and flexible welding equipment have raised high expectations for improved quality and economic feasibility. In this study, the fillet welding of a low alloyed structural steel was studied using a 10 kW fiber laser. Plates of 8 mm thick AH36 were welded as a T-joint configuration in flat (1F) and horizontal (2F) positions using either an autogenous laser welding or a hybrid laser arc welding process. The effect of heat input on the weld bead geometry was investigated using one variable at a time approach. The impact of single process parameter such as laser power of 4.5–6 kW, welding speed of 0.5–2.5 m/min, beam inclination angle of 6°–15°, focal point position of −2 to +2 mm, and welding positions of 1F and 2F were studied. All welds were visually evaluated for weld imperfections described in EN ISO 13919-1 standard. Penetration depth, geometries of the fusion and heat affected zones, and hardness profiles were measured. Produced joints have a high depth to width ratio and a small heat affected zone; full penetration welds with acceptable weld quality on both sides of the joint were produced. The parameter configurations for optimizing the welding processes are proposed.

Mechanical and microstructural characterization of laser-welded joints of 6013-T4 aluminum alloy

Laser beam welding may be used in the place of the traditional riveting process for the welding of the stringers to the skin in aircrafts. This work intends to investigate the mechanical behavior of laser-welded aluminum AA6013, subjected to post-welding heating treatments (PWHT). A fiber laser with an average power of 1.5 kW was used to weld two 1.6-mm-thick sheets in T-joint configuration. After welding, the samples were separated in three groups: the first just welded, the second subjected to a PWHT during 4 h at 190 °C and the third during 2 h at 205 °C. Hoop tensile tests showed that the thermal treatment at 190 °C for 4 h increased the tensile strength in 76 MPa, but the strain had decreased 4 %; the thermal treatment at 205 °C for 2 h increased maximum strength in 65 MPa, with a decrease in strain of 5 %. In T-pull tensile tests, the tensile properties of as-welded and PWHT samples remained the same. Standard S–N curve showed that the welding reduce the number of cycles to failure for the tested stairs. PWHT did not affect fatigue properties.

High Cycle Fatigue Behavior and Microstructural Characterization of 6013-T4 Aluminum Alloy Laser Welded Joints

Laser beam welding (LBW) may be used in the place of the traditional riveting process for the welding of the stringers to the skin in aircrafts. This work intends to investigate the mechanical behavior of laser welded aluminum AA6013, subjected to post-welding heating treatments (PWHT). A fiber laser with an average power of 1.5 kW was used to weld two 1.6mm thick sheets in T-joint configuration. After welding, the samples were separated in three groups: the first just welded, the second subjected to a PWHT during 4 hours at 190°C and the third during 2 hours at 205°C. Hoop tensile tests showed that the thermal treatment at 190 oC for four hours increased the tensile strength in 76 MPa, but the strain had decreased 4%; the thermal treatment at 205 oC for two hours increased maximum strength in 65MPa, with a decrease in strain of 5%. In T-pull tensile tests, the tensile properties of as-welded and PWHT samples remained the same. Standard S-N curve showed that the welding reduce the number of cycles to failure for the tested stairs. PWHT did not affect fatigue properties.

The strength of the adhesively bonded T-joints with embedded supports

In this study, mechanical properties of different T-joint configurations with embedded or non-embedded supports, subjected to tensile loading, were investigated experimentally and numerically. For this purpose, experimental studies were conducted on two different types of T-joint samples produced by using an adhesive film. Stress analyses in the T-joints were performed with a three dimensional non-linear finite element method by considering the geometrical non-linearity and non-linear material behaviors of both adhesives (FM73) and adherend (AA2024-T3). In conclusion, it can be stated that the variation of the geometry of the bonding zone, where the support was embedded, changed the stress distributions on the adhesively bonded joint. Accordingly, these variations had a strong impact on stress concentrations, the load bearing capacity and prolonged performance of these joints.

Experimental and numerical investigations of hybrid laser arc welding of aluminum alloys in the thick T-joint configuration

Abstract In the present investigation, a numerical finite element model was developed to simulate the hybrid laser arc welding of different aluminum alloys, namely 5××× to 6××× series. The numerical simulation has been considered two double-ellipsoidal heat sources for the gas metal arc welding and laser welding. The offset distance of the metal arc welding and laser showed a significant effect on the molten pool geometry, the heat distribution and penetration depth during the welding process. It was confirmed that when the offset distance is within the critical distance the laser and arc share the molten pool and specific amount of penetration and dilution can be achieved. The models and experiments show that the off-distance between the two heat sources and shoulder width have considerable influence on the penetration depth and appearance of the weld beads. The experiments also indicate that the laser power, arc voltage and type of the filler metal can effectively determine the final properties of the bonds, specifically the bead appearance and microhardness of the joints. The experiments verified the numerical simulation as the thermocouples assist to comprehend the amount of heat distribution on the T-joint coupons. The role of the welding parameters on the mechanism of the hybrid laser welding of the aluminum alloys was also discussed.

The Influences of T-Joint Core Design on No-Load Losses in Transformers

The main objective of this article is to compare the performance of transformers with respect to different core designs based on T-joint configurations of 23o, 45o, 60o, and 90o. The quantitative analysis of localized flux distribution and loss calculation is determined through the significant progress of numerical field calculations using the finite element method. The transformer core has been designed and simulated using QuickField software. From the results, it was found that the best core design is a 60o T-joint configuration in terms of the no-load losses and flux distribution.

Laser beam welding residual stresses of cracked T-joints

A damage tolerance analysis methodology for Laser Beam Welded (LBW) structures is proposed. The Residual Stresses (RSs) of LBW T-joints are initially calculated through the thermo-mechanical simulation of the LBW process. Through cracks of variable length are considered in the vicinity of the weld and the calculated RS field is introduced in the numerical calculation of the Stress Intensity Factors (SIFs). As the Finite Element (FE) models used for the thermo-mechanical simulation cannot be the same to those required for the fracture analysis, a special numerical routine based on interpolation techniques is applied for the transfer of RS field to the fracture mechanics FE model. The computation of SIFs at the crack front is performed for mode-I external loading. The RS effect of various cracked T-joint configurations on the SIF values at different through-the-thickness locations is studied. It is shown that both the RS field, as well as the other studied parameters, have a significant influence on the calculated stress intensity factor values.

Autogeneous Laser and Hybrid Laser Arc Welding of T-joint Low Alloy Steel with Fiber Laser Systems

This paper is focused on the welding of low alloy steels S355 and AH36 in thicknesses 6, 8 and 10 mm in T-joint configuration using either autogeneous laser welding or laser-arc hybrid welding (HLAW) with high power fiber lasers. The aim was to obtain understanding of the factors influencing the size of the fillet and weld geometry through methodologically studying effects of laser power, welding speed, beam alignment relative to surface, air gap, focal point position and order of processes (in case of HLAW) and to get a B quality class welds in all thicknesses after parameter optimization.

Laser Welding of Large Scale Stainless Steel Aircraft Structures

In this paper a welding process for large scale stainless steel structures is presented. The process was developed according to the requirements of an aircraft application. Therefore, stringers are welded on a skin sheet in a t-joint configuration. The 0.6 mm thickness parts are welded with a thin disc laser, seam length up to 1920 mm are demonstrated. The welding process causes angular distortions of the skin sheet which are compensated by a subsequent laser straightening process. Based on a model straightening process parameters matching the induced welding distortion are predicted. The process combination is successfully applied to stringer stiffened specimens.

Numerical Simulation of Welding Residual Stress Distribution on T-joint Fillet Structure

Fillet welding is widely used in the assembly of ships and offshore structures. The T-joint configuration is frequently reported to experience fatigue damage when a marine structure meets extreme loads such as storm loads. Fatigue damage is affected by the magnitude of residual stresses on the weld. Recently, many shipping registers and design guides have required that the fatigue strength assessment procedure of seagoing structures under wave-induced random loading and storm loading be compensated based on the effect of residual stresses. We propose a computational procedure to analyze the residual stresses in a T-joint. Residual stresses are measured by the X-ray diffraction (XRD) method, and a 3-D finite element analysis (FEA) is performed to obtain the residual stress profile in the T-joint. The proposed finite element model is validated by comparing experiments with computational results, and the characteristics of the residual stresses in the T-joint are discussed.

CFRP/Al하니콤 샌드위치 복합재 T-Joint 구조물의 기계적 물성에 대한 실험적 연구

Application of composite structures on naval ships strongly depends on the mechanical strength and collapse behavior of the T-joints of the whole structure. Because of the weight advantages over single skin composite and bolt fastening joining, three types of T-joints using both honeycomb sandwich composite and adhesive bonding were suggested to determine the effect of T-joint configuration. It was found that joining with a urethane foam block and overlaminates using the secondary co-bonding technique improves T-joint strength.<BR>

Occurrence of defects in laser beam welded Al-Cu-Li sheets with t-joint configuration

In the aerospace industry, laser beam welding has been considered as one of the most promising routes among the new manufacturing processes. Substitution of riveting by laser beam welding of aircraft structures has contributed to weight and cost savings. Concurrently, new aluminum alloys have been developed with the addition of lithium with better mechanical properties and lower density. The Al-3.5%Cu-1.1%Li alloy (AA2198) is one of these new generation alloys. However, laser beam welding of Al-alloys expectations might be greatly reduced by the occurrence of two main defects: porosity and hot cracking. Porosity is mainly caused by the entrapment of lithium gases, followed by rapid solidification. On the other hand, hot cracking happens due to the conjunction of tensile stresses, which are transmitted to the mushy zone by the coherent solid underneath, and to an insufficient liquid feeding to compensate for the volumetric changes. This work intended to contribute towards the knowledge of AA2198 welding metallurgy, utilizing a 2-kW-ytterbium-doped fiber laser. The T-joint configuration welds were performed autogenously or with the addition of an AA4047 filler ribbon. All the weld beads presented high porosity level, but with a decreasing tendency when welding from both sides. The use of the filler material could solve hot cracking problem. The best results are observed using two runs (both sides) with filler and a speed of 2 m/min and power of 1,200 W. The T-pull tensile strength obtained under these conditions was 178 MPa, which is below the tensile strength of the unwelded AA2198 sheet but higher than the AA6013 welded in similar conditions.

Finite element analysis of metallurgical phase transformations in AA 6056-T4 and their effects upon the residual stress and distortion states of a laser welded T-joint

Aircraft industry makes extensive use of aluminium alloy AA 6056-T4 in the fabrication of fuselage panels using laser beam welding technique. Since high temperatures are involved in the manufacturing process, the precipitation/dissolution occurrences are expected as solid state phase transformations. These transformations are likely to affect the residual distortion and stress states of the component. The present work investigates the effect of metallurgical phase transformations upon the residual stresses and distortions induced by laser beam welding in a T-joint configuration using the finite element method. Two separate models were studied using different finite element codes, where the first one describes a thermo-mechanical analysis using Abaqus; while the second one discusses a thermo-metallo-mechanical analysis using Sysweld. A comparative analysis of experimentally validated finite element models has been performed and the residual stress states with and without the metallurgical phase transformations are predicted. The results show that the inclusion of phase transformations has a negligible effect on predicted distortions, which are in agreement with the experimental data, but an effect on predicted residual stresses, although the experimentally measured residual stresses are not available to support the analyses.