Weld Profile Research Articles

Study on temperature- microstructure- stress fields of thick-walled plate welded by hybrid laser arc welding

The 25mm DH36 steel was welded by hybrid laser arc welding (HLAW), and a sequence coupled thermal-metallurgical-mechanical (TMM) model was developed based on SYSWELD. The temperature-microstructure-stress fields are predicted by simulation verified by experiment. The ratio between the arc and laser energy showed a significant effect on weld profile. The laser provided the main power and ensured deep penetration, and the arc power showed a dominant effect on the bead width of the hybrid weld during HLAW. For the hybrid welding of a thick-walled plate, the microstructure and thermal cycles varied along with the thickness. The weld profile and microstructure were experimentally characterized. The 3-pass welding procedure produced larger welding residual stress than the 9-pass welding procedure, and the process stability is poorer than the 3-pass welding process. Overall, numerical results matched well with experimental results.

Heat transfer at the step of a CANDU calandria during a severe accident

Abstract During the in-vessel stage of a severe accident in a CANDU 6 reactor, decay heat from a collapsed core would be rejected through the calandria walls into the surrounding water. At the step in the calandria wall, the subshell and annular plate meet at a right angle pointing into the calandria. The geometry at this joint could concentrate the exiting heat flux, potentially leading to calandria failure. Finite element analysis is used to study the heat transfer near the welded joint. Different weld profiles, boundary conditions, and decay heat characteristics are considered, and the local concentration of exiting heat flux is calculated.

Vision sensing and feedback control of weld penetration in helium arc welding process

Consistent joint penetration is essential to mechanical properties of weldments, yet difficult to realize in gas tungsten arc welding due to heat accumulation, varying welding conditions, and uncertain disturbance, especially for manufacturing large-scale structural components. The solution is to monitor welding penetration in real-time and implement closed-loop control. In this paper a directional light-assisted vision sensing scheme is proposed to measure the transient profile of the backside weld pool/bead for monitoring and further controlling the joint penetration state. The developing zone and the developed zone of the backside weld bead are recognized, helping determining its final width. And the relationship between the transient backside bead width and the corresponding final width is established. Furthermore, the backside bead profile is employed as a feedback signal and the closed-loop control of weld formation is implemented to achieve full penetration and a constant backside bead width. A multiple-input single-output model predictive controller is utilized in the control system, creatively combined with an anti-windup integrator eliminating the steady-state error caused by nonlinearity in welding. Experimental results have proved that the developed control system is effective in keeping a consistent backside bead width with a rapid response, a small overshoot and robustness against varying heat transfer conditions.

Fatigue Performance of Thin Laser Butt Welds in HSLA Steel

This work is focused on understanding the significant factors affecting the fatigue strength of laser-welded butt joints in thin high-strength low-alloy (HSLA) steel. The effects of the weld profile, imperfections, hardness, and residual stresses were considered to explain the results found in the S-N curves of four welded series. The results showed acceptable fatigue strength although the welded series presented multiple-imperfections. The analysis of fatigue behavior at low stress levels through the stress-concentrating effect explained the influence of each factor on the S-N curves of the welded series. The fatigue limits of the welded series predicted through the stress-concentrating effect and by the relationship proposed by Murakami showed good agreement with the experimental results.

Numerical simulation of the temperature field, weld profile, and weld pool dynamics in laser welding of aluminium alloy

A transient 3-d thermo-fluid model is developed to simulate the heat transfer and weld pool dynamics during the deep penetration laser welding of aluminium alloy AA2024. Numerical modelling and non-dimensional analyses are carried out to investigate the effect of driving forces on melt pool dynamics and geometry. The temperature-driven surface tension and its influence on weld pool geometry is analysed quantitatively by varying the input parameters. The normalised dimensions of the weld pool are plotted against dimensionless numbers viz. Peclet, Reynolds, Marangoni numbers to understand the uncertainty and changes in the process. The melt flow in weld pool is found to be laminar for the considered combination of material and process parameters. The conclusions derived in this work could explain the Marangoni convection in materials with a negative gradient of surface tension and provide an insight into the defects formation and their reduction in laser welding of aluminium alloys. The developed model is validated with experimental data and found in good agreement.

Robotic welding for filling shape-varying geometry using weld profile control with data-driven fast input allocation

Robotic multi-pass welding for thick and shape-varying weld geometry is a challenging problem. To achieve good weld quality, desired welding profile for the whole welding bevel is necessary, which requires the welding inputs to be changed appropriately in real-time. In this paper, a welding profile control with data-driven fast input allocation (PC-FIA) algorithm is proposed for robotic multi-pass welding on a shape-varying weld geometry, namely, TYK pipe-to-pipe joint. Firstly, the H∞ control algorithm is used for the welding profile control in order to suppress the error propagation during the multi-pass welding. Secondly, the welding input parameters including torch traveling speed and weaving parameters are allocated using a max−min optimization based on the identified weld input constraint from a data-driven approach. Experimental results show that the weld profile using the proposed method achieves 60% decrease of root-mean-square error with respect to the planned reference, as compared to the case of without using the proposed PC-FIA method. In addition, the allocated weaving parameters ensure that the welding inputs are always maintained within the polyhedral constraint and the whole welding quality is acceptable by industry standard.

Experimental and Finite Element Study of Polymer Infilled Tube-in-Tube Buckling Restrained Brace

This study presents a tube-in-tube buckling-restrained brace (BRB) infilled with lightweight and rapid hardening polymer. The proposed BRB consists of a circular or square tube core encased with a tube of similar shape and polymer infill. The tube-in-tube arrangement minimizes the filler material volume and enables the use of rolled steel section as opposed to welded profiles commonly utilized when large BRB axial strength is required, although welded profiles suffer from low assembly accuracy resulting from welding deformation. The infilled polymer has a density of approximately half that of mortar and requires a curing time of 24 h, enabling weight and fabrication time reduction. The stability and inelastic deformation capability of the BRB were investigated through brace and subassembly tests of six circular and four-square full-scale specimens, followed by finite element analysis. The test results show that circular BRB designed with a Pcr/Py ratio of 1.46 exhibited a stable hysteresis up to 1.42% and 1.06% core strain in tension and compression, respectively. Circular and square specimens designed with Pcr/Py ratios ranging from 0.82 to 1.06 exhibited stable hysteresis before failing by global buckling at compressive core stains ranging from 0.86% to 1.09%. The slot weld detail adopted for welding core projection stiffener displayed a stable performance in circular BRB specimens, while it resulted in large plastic strain demand in square BRB specimens, leading to core fracture at tensile core strains ranging from 0.64% to 0.71%.

Influence of Heat Inputs on Weld Profiles and Mechanical Properties of Carbon and Stainless Steel

This study examines the effect of heat input on the weld bead profile, microstructure and mechanical properties of single V- joint welded carbon and stainless-steel plates. The as-received sample steel plates were sectioned into eight pieces; dimension 75 X 30 X 10 mm thicknesses. Shielded metal arc welding (SMAW) of heat inputs 1250 and 2030 J/mm was used to produce full penetration bead on the plates. Although visual inspection indicated that some of the welds were macro defect free, austenitic stainless steel exhibited more weld distortions than the carbon steel and this was partially attributed to its lower carbon content and the width to depth aspect ratio of the weld profile aside the magnitude of the induced stress. For the carbon steel, as the heat input increased, the hardness value of both the heat affected zone and fusion zone increased. In contrast, for stainless steel, the hardness values were reasonably comparable within same weld region (HAZ or FZ) irrespective of heat input. Furthermore, the ultimate tensile strength of the stainless steel decreased as heat input increased while the ductility increased with an increase in heat input, in contrast to carbon steel, where both ductility and ultimate tensile strength generally decreased.

The Influence of Laser Power and Butt Gap on the Droplet Transfer and Weld Formation of Laser Arc Hybrid Welding

In this study, an 8mm thick AH36 steel plate was welded using laser + MAG hybrid welding technology. The results show that when the laser power is low, the droplet transition form is droplet transition, the droplet size is larger, and the transition frequency is low. As the laser power increases, the form of droplet transition is jet transition, the droplet size is small, and the transition frequency is high. When the laser power is low, the undercut phenomenon of the weld is serious. With the increase of the laser power, the undercut phenomenon of the weld is improved. Besides, the weld width and welding seam reinforcement will also increase. Laser-arc hybrid welding has a certain gap adaptability. When the laser power is 10KW, the weld profile of 0mm welding gap and 1mm welding gap are basically the same. Properly reducing the laser power is conducive to the larger welding assembly gap of laser arc hybrid welding.

Experimental and Numerical Study of the Elastic SCF of Tubular Joints.

This paper provides data on stress concentration factors (SCFs) from experimental measurements on cruciform tubular joints of a chord and brace intersection under axial loading. High-fidelity finite element models were generated and validated against these measurements. Further, the statistical variation and the uncertainty in both experiments and finite element analysis (FEA) are studied, including the effect of finite element modelling of the weld profile, mesh size, element type and the method for deriving the SCF. A method is proposed for modelling such uncertainties in order to determine a reasonable SCF. Traditionally, SCF are determined by parametric formulae found in codes and standards and the paper also provides these for comparison. Results from the FEA generally show that the SCF increases with a finer mesh, 2nd order brick elements, linear extrapolation and a larger weld profile. Comparison between experimental SCFs indicates that a very fine mesh and the use of 2nd order elements is required to provide SCF on the safe side. It is further found that the parametric SCF equations in codes are reasonably on the safe side and a detailed finite element analysis could be beneficial if small gains in fatigue life need to be justified.

Effect of Weld Profiles on Fatigue Performance of Deck to U-Rib Weld in Orthotropic Steel Deck

Effect of Weld Profiles on Fatigue Performance of Deck to U-Rib Weld in Orthotropic Steel Deck

Study of Cross-Combination and Square-Combination Configuration Magnetic Field on Tungsten Inert Gas Welding

In this study, cross-combination and square-combination configuration of the permanent external magnet were used in tungsten inert gas welding process. The external magnetic field effect to the arc plasma was observed using two cameras from the front view and side view. The depth of penetration and weld profile was investigated after welding. In this study, two types of magnets were employed; a 3 mm magnet with intensity ranging from 270-280 mT and a 5 mm magnet with 400-415 mT. Each configuration has three sub-configurations: forward, backward, and side, so there were 12 parameters in this study. The result shows that a cross-combination 5 mm magnet can increase weld penetration in any position, forward, backward or side deflection, and improve the depth-to-width ratio, however using 3 mm magnet did not influence the penetration significantly. Cross-combination has more stiffness and stability of the arc than square-combination. Most configurations have the same size weld bead width. Square combinations had fluctuated result, stiffness and stability of the arc was poor. This investigation aims to enlarge our understanding of the magnetic field effect on the arc plasma and the weld profile. In future, the arc blow effect from the external magnetic field can be controlled and regulated to improve TIG welding performance.

Stress concentration factors for multi-planar DKT tubular truss joints under axially balanced loads

This paper presents a set of empirical equations to predict stress concentration factors (SCFs) in multiplanar right-angle DKT-joints. The SCFs were obtained from linear elastic finite element analyses, wherein the weld profiles were carefully modelled. The modelling techniques were first verified against previous experiments on steel and acrylic test specimens and were found to yield accurate predictions. Parametric studies encompassing a total of 54 DKT-joint models, including two different loading conditions, were performed. The SCFs from 8 locations around the perimeters of the middle and outer braces on the chord side were extracted from the models. The carry-over effect in the unloaded braces was carefully included in the investigation. The resulting SCF database was used to derive empirical parametric equations for the SCFs in DKT-joints using non-linear regression analysis.

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.

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.

K-MDTSC: K-Multi-Dimensional Time-Series Clustering Algorithm

The increasing capability to collect data gives us the possibility to collect a massive amount of heterogeneous data. Among the heterogeneous data available, time-series represents a mother lode of information yet to be fully explored. Current data mining techniques have several shortcomings while analyzing time-series, especially when more than one time-series, i.e., multi-dimensional timeseries, should be analyzed together to extract knowledge from the data. In this context, we present K-MDTSC (K-Multi-Dimensional Time-Series Clustering), a novel clustering algorithm specifically designed to deal with multi-dimensional time-series. Firstly, we demonstrate K-MDTSC capability to group multi-dimensional time-series using synthetic datasets. We compare K-MDTSC results with k-Shape, a state-of-art time-series clustering algorithm based on K-means. Our results show both K-MDTSC and k-Shape create good clustering results. However, K-MDTSC outperforms k-Shape when complicating the synthetic dataset. Secondly, we apply K-MDTSC in a real case scenario where we are asked to replace a scheduled maintenance with a predictive approach. To this end, we create a generalized pipeline to process data from a real industrial plant welding process. We apply K-MDTSC to create clusters of weldings based on their welding shape. Our results show that K-MDTSC identifies different welding profiles, but that the aging of the electrode does not negatively impact the welding process.

Static capacity of tubular X-joints reinforced with fiber reinforced polymer subjected to compressive load

In the present paper, the initial stiffness, the ultimate capacity, the capacity ratio, and the failure mechanisms of the tubular X-joints reinforced with Fiber Reinforced Polymer (FRP) under compressive load are investigated. For these aims, a finite element (FE) model was generated and verified with the available experimental data. Afterward, 109 finite element (FE) models were created to investigate the efficacy of the FRP layers (length, number, and orientation) and the connection geometry (β, τ, and γ) on the static performance of the reinforced X-joints. In the FE models, the effects of the weld profile and the contact between the FRP and the members (chord, weld, and braces) were considered. Results showed that the FRP can remarkably enhance the stiffness, ultimate capacity, and improve failure mechanisms. Despite the notable effect of the FRP on the performance of the joints, there is not any study on the X-joints with FRP. Hence, after the parametric study, the FE results were used to propose a theoretical formula, based on the yield body model, to predict the ultimate strength of X-joints with FRP. In addition, the proposed formula is confirmed by the acceptance criteria of the UK Department of Energy.

Generalized SCF Formula of Out-Of-Plane Gusset Welded Joints and Assessment of Fatigue Life Extension by Additional Weld.

The existing S-N curves by effective notch stress to assess the fatigue life of gusset welded joints can result in reduced accuracy due to the oversimplification of bead geometries. The present work proposes the parametric formulae of stress concentration factor (SCF) for as-welded gusset joints based on the spline model, by which the effective notch stress can be accurately calculated for fatigue resistance assessment. The spline model is also modified to make it applicable to the additional weld. The fatigue resistance of as-welded and additional-welded specimens is assessed considering the geometric effects and weld profiles. The results show that the error of SCFs by the proposed formulae is proven to be smaller than 5%. The additional weld can increase the fatigue life by as great as 9.4 times, mainly because the increasing weld toe radius and weld leg length lead to the smaller SCF. The proposed series of S-N curves, considering different SCFs, can be used to assess the welded joints with various geometric parameters and weld profiles.

Hardness distribution and aging response associated with precipitation behavior in a laser pressure welded Al–Li alloy 2198

Abstract Although laser welded Al–Li alloys show great potential for application in aerospace industry, the detailed relationship between local hardness and complex microstructure remained unclear. In the present study, relationship between precipitation behavior and local hardness in a defect-free laser pressure weld of Al–Li alloy 2198 was systematically examined by transmission electron microscopy. Hardness profile of the laser pressure weld was reduced in the vicinity of the weld center, mainly explained by size and density of the strengthening precipitates. Moreover, post-weld aging increased the density of strengthening precipitates in the precipitate-dissolved regions, increasing their hardness values markedly. On the other hand, a few precipitates were formed in the precipitate-coarsened regions during post-weld aging, which slightly increased the local hardness. The variation in hardness during post-weld aging could be well correlated with the precipitation behavior in each region of the laser pressure weld.

Evolution Mechanism of Transient Strain and Residual Stress Distribution in Al 6061 Laser Welding

Considering the harm that residual stress causes to the mechanical properties of a weld joint, the evolution mechanisms of transient strain and residual stress distribution are investigated in laser welding of Al 6061, considering that these originate from non-uniform temperature distribution and are intensified further by the unbalanced procedure of melting and solidification. Thermal-elastic-plastic finite element method is developed and analyzed, while the actual weld profile is novel fitted by a B-spline curve. Transient strain is extracted by strain gauges. Longitudinal strain starts from a fluctuating compressive state and progresses to an ultimate residual tension state at the starting and ending welding positions, respectively. The maximum fitting deviation of the weld profile is 0.13 mm. Experimental and simulation results of residual strain are 842.0 μ and 826.8 μ, with a relative error of 1.805% at the starting position and −17.986% at the ending position. Near the weld center, mechanical behavior is complexly influenced by thermal expansion and contraction in the weld zone and the reaction binding force of the solid metal. Within a distance between −10 mm and 10 mm, and longitudinal stress is in a tension state, transverse stress fluctuates with a high gradient (~100 MPa).