Weld Geometry Research Articles

Numerical investigation and prediction of grain size in different friction stir welding areas of AA6061 aluminum alloy

Friction stir welding is a solid-state bonding technique based on two factors, a pressure greater than the material yield stress and large plastic deformation. The final joint between parts takes place in different welding geometries by using these two factors. The grain sizes in the weld areas are influenced by recovery, recrystallization, and grain growth. In the current research, using an analytical-numerical method based on finite element simulation of friction stir welding of AA6061-T6 alloy, the grain sizes in various welded areas have been predicted. The finite element simulation has been performed based on the coupled Eulerian-Lagrangian approach using ABAQUS software and the results have been verified by experiments. The predicted results were in good agreement with the experimental results. Due to the concentration of heat and plastic flow in the central region of the weld, the stirring region had the most microstructural changes and the grain size in this region decreased more sharply than other different areas of the weld. As the rotational welding speed increases, recrystallization phenomena in the central weld area increases. With increasing the translational welding speed, grain size increased in different welding areas. This increase occurred more severely in the central area of the welded joint.

Two-Stage Model for Fatigue Life Assessment of High Frequency Mechanical Impact (HFMI) Treated Welded Steel Details

Welded steel details are critical components from the aspect of fatigue. Additional fatigue resistance can be achieved by the High-Frequency Mechanical Impact (HFMI) treatment. This treatment increases the crack initiation period by improving the weld geometry, introducing compressive residual stresses, and increasing the weld toe’s hardness. The study presented in this paper is based on the development and calibration of an Initiation–Propagation-based Two-Stage Model (TSM), which is, by the combination of different methods, suitable to separately consider crack initiation and crack propagation. It is shown that a TSM is able to predict the fatigue life of as-welded and HFMI-treated welded steel details, which is proven by comparing the calculated results with the results of tests on similar details given in the literature. A parametric study of the TSM is conducted for different steel grades in order to investigate the influence of steel strength and HFMI parameters on fatigue lives of a welded steel detail with longitudinal attachment.

Effect of weld geometry parameters on dynamic behavior of buried X70 steel pipeline under subsurface detonation

Although a significant amount of research has been conducted to investigate the deformation and failure of buried pipelines subjected to load disturbance, scarce information is available about the effect of weld geometry parameters on the dynamic behavior of buried pipelines under blast loads. In the present study, numerical method and range analysis method were conducted to investigate the effect of weld geometry parameters including bevel angle, residual weld height, weld root opening, and thickness of root face on the dynamic performance of welded X70 steel pipelines under subsurface detonation. The results showed that the deformation of explosion-front surface is larger than that of explosion-back surface of the buried pipeline. The bevel angle, residual weld height, and thickness of root face have different effects on the dynamic comparison index of the welded pipes including peak vibration velocity, peak equivalent stress, peak equivalent strain, and peak displacement. Reasonable configuration should be adopted to properly select the geometry and dimensions of welding groove due to the complex influence of the weld geometry parameters. Combined the present results with the designing practice and current standards, the suggested weld geometry parameters to decrease their effects on the dynamic behavior of the welded X70 steel pipeline are as follows: the bevel angle (25 ± 5°), residual weld height (less than 1 mm), weld root opening (3.5 ± 0.5 mm), and thickness of root face (1.6 ± 0.6 mm).

Processing modes in laser beam oscillating welding of Al 6Cu alloy

The laser-materials interaction is crucial for laser material processing. In this paper, the laser beam oscillating welding (LBOW) was used to weld 2219 Al6Cu alloy sheets. The effects of the welding parameters on the processing modes were studied. The differences of weld geometry, internal defects, and microstructure between different modes were investigated, and the laser-material interaction process in different modes was discussed. The results indicated that the LBOW process could be classified into three modes: 1) keyhole mode, 2) transition mode, and 3) conduction mode. In the keyhole mode, the oscillating keyhole pushed the molten pool to flow in a vortex, which improved the stability of the welding process. As the oscillating speed increased, the laser absorption rate decreased. When the laser energy absorbed by the liquid metal was not sufficient to form a keyhole, the keyhole mode transited to the transition mode. In the transition mode, the laser irradiated into the vapor depression without multiple reflections. There was almost no porosity generated in the laser weld. When the laser absorption rate was further reduced, the transition mode changed to the conduction mode. In the conduction mode, the material evaporation hardly occurred. Only a few metals on the surface melted.

A review on TIG welding technology variants and its effect on weld geometry

This paper focuses on the major developments in the tungsten inert gas (TIG) welding technology for improving weld penetration depth during the welding process. TIG welding is an established arc welding process and it is extensively used for welding thin sections of almost all ferrous and non-ferrous material. However, the growing interest of industries in utilizing the process for welding mid-thick sections components led to numerous innovation in the TIG welding process. In this article, major variants of the TIG welding process i.e. pulse TIG, activated TIG, keyhole TIG, multi-electrode TIG welding process and its associated mechanism is described to understand the concept of improvement in weld penetration depth during the welding process. Furthermore, a systematic discussion on weld bead geometry obtained by different TIG welding process, starting from the mid of 2000 s to till date is presented. The major motive of this review paper is to explore the potential of the TIG welding process and provide a state-of-the-art to the industries as well as the academic world.

Modeling and optimization of weld bead profile with varied welding stages for weathering steel A606

The profile of the welding bead changes with the welding process parameters during the gas metal arc welding (GMAW) process, the top reinforcement disappears, and the penetration becomes sunken when the excessive welding heat input is applied. However, little research work is specially planned to cope with the studying of welding bead under these circumstances. A systematic study of the relationships among the welding process variables and welding bead geometric features as well as optimization of the welding quality is presented. The influences of the welding technological parameters (voltage, welding speed, and wire feed speed) on the welding geometry were revealed, and the models correlating them were established. The features of the weld bead geometry were composed of top reinforcement width, top reinforcement height, penetration depth, bottom reinforcement width, and bottom reinforcement height. By the desirability function approach, the recommendation of suitable welding parameters to meet the contradicting demands of multiple bead geometric features is fulfilled. The microstructure in different welding regions and mechanical performances of the welding joints produced by the verification test were also studied.

Electron-Beam Welding of Laser Powder-Bed-Fused Inconel 718

This study explores the application of Electron-Beam Welding (EBW) for joining Laser Powder-Bed-Fused Inconel 718 (L-PBF IN718) superalloy. Three different levels of electron beam speed and beam current were explored to give nine different electron beam heat inputs for experimentation. To define the weld characteristics microhardness, tensile, and fractography analysis using scanning electron microscopy, optical microscopy, and energy dispersive spectroscopy were conducted. Typical nail-shaped weld geometry was observed with penetration depth proportional to heat input. Most welded samples exceeded the yield strength (600MPa) and tensile strength (920MPa) requirements from the ASTM F3055 specifications for additively manufactured IN718, however, the specimens did not meet the ductility requirements (27%). Brittleness of the weld was attributed to the presence of brittle secondary phases in the weld matrix, and unfused metal powder of adjacent L-PBF layers. Post-processing heat treatments were recommended to improve the weld quality while improving the ductility of EBW joints.

Numerical and databased investigations on the fatigue of cruciform joints with gaps

The paper deals with investigations on the fatigue resistance of the load-carrying cruciform joint with gaps. The aim is to define limits of specific acceptable imperfections, since these do not always necessarily affect the fatigue strength. Different geometrical influences on the fatigue strength of the load-carrying cruciform joint with gaps are analysed numerically. Numerical simulations comprise effective notch stress calculations, which have been compared to fatigue test results from literature, documented in a fatigue test database. A larger gap in combination with a smaller weld size leads to the unfavourable failure at the weld root. For the specific geometrical configurations, borderline functions defining the failure location on the basis of local weld geometry have been defined. Finally, the most interesting configurations are presented, which will be tested experimentally in a subsequent fatigue test program.

“ICMPC” Effects due to tool design during FSW process of aluminium alloy AA7075 T-6

ABSTRACT The present study explores the implications of friction stir welding (FSW) geometries of instruments on AA7075 T-6 welds. For tougher materials, it is assumed that threaded FSW instruments are beneficial, like AA7075 T-6. However, the structure of the tool shoulder and the concavity of the shoulder surface also play an important role in determining the quality characteristics of friction stir welds. The effect of threaded FSW instruments on using various shoulder diameters, pin diameters, AA7075 aluminium alloys were investigated. Diameters, concavity of the shoulder surface and speeds. Experiments were to research the effects of these instruments on welds of AA7075 with respect to welding cross-sectional area, tensile strength, and percent elongation. A mathematical trend using response, the effects of the tool geometries on the welds were predicted to the regression analysis of surfaces, diameter of the shoulder and concavity of the shoulder surface. The relationship effects of the control variables (geometrical parameters of the instrument) on the responses such as weld power, weld cross segment and percent elongation have been investigated. The modelling approach developed in this study was found to be sufficient to predict the effects of the FSW instrument welding geometrical variables.

Decisive impact of Filler-free joining processes on the Microstructural evolution, tensile and impact properties of 9Cr-1Mo-V-Nb to 316 L(N) dissimilar joints

Filler-free (FF) welding processes namely, Activated Tungsten Inert Gas welding (ATIG), Laser Beam Welding (LBW), and Friction Stir Welding (FSW) were utilized for joining the nuclear grade 9Cr-1Mo-V-Nb ferritic-martensitic steel and 316 L(N) austenitic stainless steel. A comparative investigation was made by assessing the weld geometries, metallurgical features, material mixing proportions, carbon diffusion behaviour, and mechanical properties of the post-weld heat-treated (PWHT) dissimilar weld joints. Geometries of the weld zones were observed with the transverse and longitudinal macrographs. Metallurgical features were examined by optical microscopy (OM) and Scanning electron microscopy (SEM). Three-phase microstructures were identified in the dissimilar weld zones (DWZ). The elemental distributions were identified by Energy-dispersive X-ray spectroscopy (EDAX). The mixing proportions of the dissimilar alloys and the formation of δ-ferrite in the dissimilar heat-affected zones (HAZ) and DWZ were analytically quantified. Moreover, the diffusion activity of carbides/interstitial carbon atoms was examined by Secondary ion mass spectroscopy (SIMS). In the FSW joints, the intermingled microstructures are recorded with high and stabilized hardness values as compared to the DWZ of the ATIG and LBW joints. In the transverse tensile test, all FF joints were failed at the 316 L(N) base metal (BM) region. Tensile and impact testing of all weld metal indicated that, the weld metal region of the LBW joint exhibited higher strength and lower toughness as compared to the ATIG and FSW joints. The presence of untransformed, recrystallized fine equiaxed austenite along and refined martensitic structure arranged in an alternate layers within the weld metal region of FSW joint caused the higher toughness property than the ATIG and LBW joints.

Pulsed Nd: YAG Laser Parameters Effect on Welding Uncoated Advance High Strength Steel (AHSS) for Automotive

Pulse wave (PW) welding technique has become more adequate process to produce a deep penetration welding with smaller fusion zone and heat affected zone for automotive steel joint. A 1.6 mm thickness of N22CB boron steel from advance high strength steel (AHSS) type was welded by using PW mode from a low power Nd: YAG laser. The process parameters studied in this paper are pulsed energy, Ep, focal length, F, and welding speed, S. Bead-on-plate (BOP) welding was used in this experiment. The effect of parameters on the weld pool geometry was studied. Higher pulsed energy gives high weld penetration and higher weld width, contributing to the bigger weld pool size. Positive defocus position of focal length produces weld geometry with high penetration depth and smaller bead width compared to negative defocus position. Lower welding speed could produce deep penetration depth as the high heat input produced.

Effects of wheelset flexibility on locomotive–track interaction due to rail weld irregularities

Irregularities of rail joints ordinarily induce high-frequency impacts on wheel–rail contact systems, which may further influence vehicle–track interaction. In this study, a three-dimensional locomotive-track coupled dynamics model that uses the wheelset flexibility was developed. The wheelset rigid motion and elastic deformation are calculated based on the multi-body dynamics theory and finite element method, respectively. The effectiveness of this model was validated. The effect of wheelset flexibility on locomotive–track interaction due to rail weld irregularities is analysed by comparing the dynamic responses obtained using the rigid model and the proposed rigid–flexible coupled model. The proposed model is applied to the sensitivity analysis of the wheelset response to the rail weld geometry irregularity. The results show that the dominant frequency of the wheel–rail force or axle–box acceleration is 81 Hz, which is the 1st bending modal frequency of the wheelset. The P2 resonance frequency is easily excited owing to impacts of rail weld irregularities, which may induce the formation of locomotive wheel polygonization. The wheelset acceleration was more sensitive to the wavelength than the depth of the rail weld irregularities. The wavelength characteristics can be significant in vehicle vibration-based condition monitoring of rail weld irregularities.

Isogeometric Analysis and Bayesian Optimization on Efficient Weld Geometry Design for Remarkable Stress Concentration Reduction

Shape optimization combined with Isogeometric Analysis will be an efficient design method since exact Computer Aided Design geometries can be used for numerical analysis thanks to the same basis functions. In this study, authors developed an in-house research software JWRIAN-IGA and applied it to optimize the weld geometries of two models, namely a T-joint fillet weld and an elongated boxing fillet weld to reduce stress concentration. A gradient-free stochastic global optimization algorithm, Bayesian Optimization was used to sought optimal geometry parameters. It was shown that the optimized geometry was efficiently designed and the stress concentration in the welds for both cases was greatly reduced.

Peridynamic analysis of fatigue crack growth in fillet welded joints

Fatigue assessment is one of the significant factors to be considered for estimating design life of structures and structural reliability during operation. Especially, for welded structures, high stress concentration, residual stresses, weld geometry and weld quality make the structure more vulnerable to fatigue failures. Therefore, approaches that are more effective are required for estimating fatigue performances of welded structures. Existing classical methods to predict the crack propagation under cyclic loadings have some difficulties in treating complicated patterns of crack growth. However, peridynamic theory has advantages on dealing with discontinuities. In this study, a peridynamic fatigue model, which is a bond damage model of remaining life, is validated by considering ASTM E647 standard compact tension test for the crack growth. After validating the PD model, the fatigue performance of the fillet welded joint is presented by predicting the fatigue crack growth under cyclic loading conditions.

A study on simulation analysis for laser-welded I-core sandwich plate with different material properties and T-joint weld characteristic

Stiffness and strength of sandwich plate vary depending on similar (SI) or dissimilar (DSI) material element (faceplate or core) and laser weld geometry. The issues of I-core sandwich plate characteristics are essential to attain practical sandwich plate application. Hence, research on different material properties and T-joint weld characteristics of I-core sandwich steel plate presents a positive understanding of various character factors that affect sandwich plate bending performance. In this paper, the I-core sandwich steel plate characteristic was investigated using finite element analysis (FEA). The 3-point bending with a fine meshing, interaction of elements, and load applied was kept constant. The partition size at the laser weld geometry is smaller, and the partition size continuously grows when further away from the weld geometry. The result shows that a combination of weak and strong material on either element will reduce I-core sandwich's stiffness and strength unless strong material is assigned at the faceplate and core. Moreover, there is a significant change when rootgap is present. This influencing the centric and eccentric of the weld. The weld width produces a perfect bending as wholesome T-joint, yet to achieve such traits is impossible in reality but possible when the weld length is closer to the length of the core. The exploration of these characteristics in response to I-core sandwich steel plate holds a good response in engaging for the multiple variables that affect the plate's stiffness and strength.

Use of a stepped preparation to improve the damage tolerance of grade 91 steel welds

ABSTRACT Damage equivalent to that seen over very long times in Grade 91 steel welded components was successfully formed in laboratory, feature sized samples tested under controlled conditions. This paper compares the creep behaviour of welds made using a typical preparation with results for novel step weld geometries. When well-designed the step geometry offsets the heat affected zone (HAZ) in the through thickness of the weld which would be equivalent to the pressure boundary in a pipe. The step in the weld profile thus provides benefit to in-service performance because it prevents the rapid link up of aligned creep cavitation that forms in the HAZ of welds made using typical preparations. The results demonstrate that a well-designed step weld geometry increases the creep rupture life and improves damage tolerance. In turn, the increased duration of stable crack growth promotes the opportunity for detection of creep damage using nondestructive testing methods.

An Approach to Improving the Mechanical Properties of Friction Stir Spot Welded Joints on the Basis of Hook Formation Mechanism

Background: Partial metallurgical bond (namely 'hook') is formed between the overlapped metal sheets during friction stir spot welding (FSSW). The geometry of hook is found to significantly affect the mechanical performance of FSSWed joints, while that how to adjust hook geometry to a better state remains to be studied. Methods: The conventional FSSW joints under different plunge depths and dwelling time were obtained. The cross-sectional morphology of each spot weld was investigated to clarify the material flow behavior and deduce the formation mechanism of hook. The tensile shear strength and fracture features were examined to reveal the effect of hook geometry on the mechanical properties. Results: The weld geometry affects the tensile shear strength of FSSWed joints by determining their fracture modes. The formation mechanism of hook is deduced by a material flow model. In the toolplunging stage, the faying interface is broken by upward-flowing materials, hook is therefore initiated and driven up gradually. During the tool-dwelling stage, hook continues to migrate to the lowpressure zone, surrounding the stir zone. Conclusion: The uncertainty of crack-propagating endpoint along hook makes it difficult to ensure the mechanical properties of welds. If the hook endpoint has not yet reached the low-pressure zone at the end of welding process, welds with ideal hook geometry can be obtained. Target friction stir spot welds were produced by the use of a tool possessing smaller pin diameter.

Laboratory-Scale Processing and Performance Assessment of Ti\u2013Ta High-Temperature Shape Memory Spring Actuators

Ti75Ta25 high-temperature shape memory alloys exhibit a number of features which make it difficult to use them as spring actuators. These include the high melting point of Ta (close to 3000 °C), the affinity of Ti to oxygen which leads to the formation of brittle α-case layers and the tendency to precipitate the ω-phase, which suppresses the martensitic transformation. The present work represents a case study which shows how one can overcome these issues and manufacture high quality Ti75Ta25 tensile spring actuators. The work focusses on processing (arc melting, arc welding, wire drawing, surface treatments and actuator spring geometry setting) and on cyclic actuator testing. It is shown how one can minimize the detrimental effect of ω-phase formation and ensure stable high-temperature actuation by fast heating and cooling and by intermediate rejuvenation anneals. The results are discussed on the basis of fundamental Ti–Ta metallurgy and in the light of Ni–Ti spring actuator performance.

Evaluation of Cyclic Loading Effects on Residual Stress Relaxation in Offshore Wind Welded Structures

Monopile foundations contain welding residual stresses and are widely used in industry to support offshore wind turbines (OWTs). The monopiles are subjected to hammering loads during installation and cyclic loads during operation, therefore the influence of residual stress redistribution as a result of fatigue cycles must be evaluated in these structures. The existing empirical models to predict the residual stress redistribution in the presence of cyclic loading conditions are strongly dependent on the material, welding process and loading conditions. Hence, there is a need to predict the residual stress redistribution using finite element simulations. In this study numerical analyses have been conducted to predict the initial state of residual stress in a simplified weld geometry and examine the influence of subsequent cyclic loads on the relaxation behavior in residual stress profiles. The results have shown that fatigue cycles have a severe effect on residual stress relaxation with the greatest reduction in residual stress values observed in the first cycle. Moreover, the numerical prediction results have shown that the stress amplitude plays a key role in the extent of residual stress relaxation in welded structures.

Selection of parameters in nanosecond pulsed wave laser micro-welding

The digital control of the latest nanosecond pulsed wave (PW) fibre lasers allows very high flexibility in controlling the application of the total energy to a workpiece, which brings several advantages to the joining process. By choosing different pulse shapes in different spatial profiles, it is possible to apply low energy per pulse with high precision and accuracy resulting in lower heat input. Since the energy of each pulse is insufficient to generate melting, these lasers operate at very high pulse repetition frequencies near continuous wave (CW) regime. Nevertheless, the peak powers of PW lasers are much higher than CW. In this research, the effect of peak power, pulse energy, pulse width, pulse repetition frequency and duty cycle has been studied. The experimental work was conducted in bead on plate of austenitic stainless steel to investigate the effect of laser on the weld geometry, i.e. depth of penetration and width. An empirical model, previously established for CW mode, which enables the achievement of a particular penetration depth independent of the beam diameter, was redesigned and tested for PW mode. The “pulse power factor model” allows the laser user to select a weld profile that meets certain quality and productivity requirements independent of the laser system. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of different system parameters by keeping a constant trade-off between pulse power factor and interaction time.