Welding Residual Stress Research Articles

Influence of Interlayer Temperature and Welding Sequence on the Temperature Distribution and Welding Residual Stress of the Saddle-Shaped Joint of Weldolet-Header Butt Welding.

In this paper, based on Simufact Welding finite element analysis software, a numerical simulation of the temperature and residual stress distribution of the weldolet-header multi-layer multi-pass welding process is carried out, and the simulation results are verified through experiments. The experimental results are in good agreement with the numerical simulation results, which proves the validity of the numerical simulation results. Through the results of the numerical simulation, the influence of the welding sequence and interlayer temperature on the temperature and residual stress distribution at different locations of the saddle-shaped weld was studied. The results show that the temperature and residual stress distribution on the header and weldolet are asymmetric, and the high-stress area of the saddle-shaped welded joint always appears at the saddle shoulder or saddle belly position. When the interlayer temperature is 300 °C, the peak residual stress reaches a minimum of 428.35 MPa. Adjusting the welding sequence can change the distribution trend of residual stress. There is no high-stress area on the first welding side of the two-stage welding path-2. The peak values of residual stresses for continuous welding path-1 and two-stage welding path-2 are 428.35 MPa and 434.01 MPa, respectively, which are very close to each other.

Finite Element Welding Residual Stress Analysis of CRDM Penetration Nozzles

Abstract This article investigates numerically welding residual stress distributions of a tube with J-groove weld in control rod drive mechanisms of a pressurized nuclear reactor vessel. Parametric study is performed for the effect of the tube location, tube dimensions, and material's yield strength. It is found that residual stresses increase with increasing the inclination angle of the tube, and the up-hill side is the most critical. For thicker tube, residual stresses decrease. For material's yield strength, both axial and hoop residual stresses tend to increase with increasing the yield strength of Alloy 600. Furthermore, axial stresses tend to increase with increasing yield strength of Alloys 82/182.

Buckling of steel column with box section considering residual stress under local fire

In order to study the fire resistance performance of the box section steel column considering the welding residual stress under local high fire temperature, a finite element model of the box section steel column was established by using ABAQUS software, and the generation of welding residual stress was simulated. Based on the simulation results, the stable bearing capacity of the box section steel column considering welding residual stress under three kinds of local fire condition was analyzed. The results show that the tensile stress is highly concentrated in the weld seam, and the welding residual compressive stress with wide distribution and uniform amplitude is generated in other parts. Under the three kinds of local fire conditions, the stable bearing capacity of the component decreases with the increase of temperature. When the maximum temperature of the component is greater than 566 °C, the stable bearing capacity of the component decreases significantly, and the decline coefficient reaches 0.62. When the fire temperature is 436°C-658°C, the stable bearing capacity of the component is the least under condition 3, which is the most unfavorable condition of the component.

Effect of residual stress in longitudinal and transverse weld on global stability of box section steel column

In order to study the influence of welding residual stress on the global stability of box section steel column, the simulation of the side effects from the welding process of Q345 box section steel column by ABAQUS thermal-structure coupling analysis was conducted. A temperature-displacement explicit analysis step was established, and the residual stress caused by the temperature difference of the welding specimen was simulated by applying the body heat flux directly to the solid element within the same thickness range of the weld seam and defining the load amplitude; The calculated welding residual stress was taken as the initial defect of the structure and the global stable bearing capacity of the box section steel column was solved by the arc length method. Considering the influence of thickness and welding residual stress on the global stability of box section steel column, the calculation results of 12 finite element models were compared. The results show that under the same body heat flux, the residual stress of steel columns with different thicknesses during welding is different, and the maximum value can reach 791MPa; Under the condition of the same residual stress, the global stability bearing capacity of the box section steel column will also change irregularity with the change of thickness, and the global stability bearing capacity can be reduced by 3.07% compared with that no residual stress.

Radial expansion approach and its mechanism to reduce residual stress and distortion of girth joint structure

In this study, a radius expansion approach to enlarge radius around welding area is proposed to reduce residual stresses and distortion for large girth joint structure. The finite element (FE) model is developed to investigate the effects of expansion on the welding residual stresses and distortion. The simulation is verified with the experiment results. With larger radius expansion, there is lower residual stresses and distortion in joint. The mechanism is discussed using thermal-elastic-plastic (TEP) strains theory of welding. The theoretical analysis reveals that elastic strain induced by radius expansion is the key factor that reduces hoop residual stress and radial shrinkage.

Investigation and Prediction of the Influence of Shielding Gas Composition on Residual Stress

Residual stresses are internal stress distribution locked up within a material or weldment area. They usually exist inside the material (or weld) irrespective of external loading. These stresses are generated upon equilibrium of materials after plastic deformation caused either by applied mechanical loads, thermal loads or phase change and they play key role in the failure of these joints. Therefore, accurate prediction and reduction of residual stress are critical in improving the quality of a weldment. Welding process generates residual stresses of various magnitudes, and the combination of shielding gases at various percentages might affect the amount of residual stresses in weldment. The resultant residual stress from shielding gas on welded joint is unknown and has been based on trial and error assumption. This study therefore, focused on the investigation and prediction of shielding gas mixtures to minimize residual stress formation in mild steel welded joint, employing scientific design of experiment using Box-Beckhen’s design (BBD) matrix, statistical and mathematical models to measure the residual stresses from various gas mixtures. The argon (Ar) and carbon-dioxide (CO 2 ) shielding gas variations considered for the experiment were: 100%wt. Ar and 0%wt. CO 2 ; 75%wt. Ar and 25%wt. CO 2 ; 50%wt. Ar and 50%wt. CO 2 ; 25%wt. Ar and 75%wt. CO 2 , 0%wt Ar and 100%wt. CO 2 . The weldment produced by shielding gas of 100%wt. Ar and 0%wt. Co 2 had the highest residual stress while the weldment of 50%wt. Ar and 50%wt. CO 2 , 25%wt. Ar and 75%wt. CO 2 , 0%wt. Ar and 100%wt. CO 2 produced weld with lesser residual stress values.

An Economical and Mechanical Investigation on Local Post-Weld Heat Treatment for Stiffened Steel Plates in Bridge Structures

A heat treatment is effective for reducing the residual stress of the welded structures. A post-weld heat treatment (PWHT) requires a large heating apparatus (furnace). It requires a high energy, a long time, and a high cost. For examining the possibility of cost and energy saving in PWHT work, an economical and mechanical investigation of the local PWHT to stiffened plate members in steel bridges was conducted. The expense of apparatus for the furnace PWHT was 1.5 times higher than that of local PWHT by sheet-type ceramic heaters. When the number of heater units was reduced and were repeatedly used, the expense for the apparatus became lower. However, it took longer to complete the heat treatment than with the furnace PWHT or the local PWHT with full heater units. The thermal elastic-plastic finite element (FE) analysis examined the effect of local PWHT. The tendency of the stress distribution after the local PWHT differed from the welding residual stress or the stress after the furnace PWHT because of the temperature difference between the heated and the non-heated parts of the local PWHT. However, the effect of residual stress relief by the local PWHT could be almost the same as that of the furnace PWHT.

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.

Prediction of welding residual stress and deformation in electro-gas welding using artificial neural network

Evaluating the welding residual stress and deformation in a reasonable and reliable way is the perquisite of ensuring the quality of weldments. Therefore, in this paper, an artificial neural network model is developed for the prediction of welding residual stress and deformation produced in Electro-gas welding using C++ language. The plate thickness, groove angle, groove clearance, welding current, cooling type and the welding material have been considered as the input parameters, the residual stress and deformation as output parameters in the structure of the model. The comparison between the neural network predictions and finite element analysis results indicates that the established neural network model is sufficiently accurate and efficient in predicting the residual stress and deformation. Additionally, a human-computer interaction interface software based on Qt environment is designed and implemented, aiming to obtain the prediction results in real time.

Influence of temperature- and phase-dependent yield strength on residual stresses in ultra-high strength steel S960 weldments

The temperature- and phase-dependent yield strength plays a decisive role in the precise prediction of residual stresses in structural steel weldments. Since it is very expensive and time-consuming to directly measure the yield strength of a given steel by experimental method, numerical simulation has commonly been performed using the available yield strength of the same steel grades in scientific literature and material database or using the evaluated data based on the empirical formulations in standards/codes for the given steel. Nevertheless, the yield strengths of the same steel grades are usually different mainly due to the disparity in chemical composition and grain size. Furthermore, there are considerable differences in the yield strength at elevated temperatures obtained from the predictive functions for the given steel. Therefore, it is necessary to clarify the influence of the variation in temperature- and phase-dependent yield strength obtained from different methods on the predicted welding residual stresses in numerical simulation. In this study, numerical sensitivity analyses have been conducted to clarify the effect of yield strength on the predicted residual stresses in ultra-high strength steel S960 weldments. Furthermore, tensile tests and welding experiments were carried out for comparison and validation. Based on the current work, the effect of temperature- and phase-dependent yield strength on the calculated welding residual stresses is clarified. Besides, the reliability of the proposed functions to evaluate yield strength based on the tensile test results mainly from mild steels and conventional high strength steels is assessed for the recently developed ultra-high strength steel S960. Finally, guidance on how to economically determine the reliable temperature- and phase-dependent yield strength for S960 steel in numerical welding simulation is provided.

Effect of Post-Weld Heat Treatment Conditions on Mechanical Properties, Microstructures and Nonductile Fracture Behavior of SA508 Gr.1a Thick Weldments

This study analyzes the effects of post-weld heat treatment (PWHT) on the mechanical properties and microstructures of SA-508 Gr.1a welds and proposes a new PWHT exemption criterion based on nonductile fracture evaluation considering welding residual stress. The welding coupons were prepared with submerged-arc welding, gas-tungsten arc welding, and shielded-metal arc welding, using ferritic steel, SA-508 Gr.1a. The microstructure of the heat-affected zone (HAZ) was analyzed using optical microscopy, electron-back-scatter diffraction and Vickers hardness testing. The mechanical properties of the welds were evaluated by uniaxial tensile test, transverse side bend test, Charpy V-notch impact test and side bend test. Bainite and ferrite structures formed mainly in the HAZ, and the grain size became coarser with proximity to the surface and fusion line. The mechanical properties did not depend strongly on PWHT, weldment thickness or welding techniques, and they satisfied the welding procedure qualification test specified in the ASME Boiler & Pressure Vessel code. Welding residual stresses were considered in assessing structural integrity using nonductile fracture evaluation. A margin of safety against nonductile fracture with residual stress was calculated for Korean Standard Nuclear Power Plant steam-generator welds, using its design parameters and operating conditions, and this safety margin is suggested as an acceptance criterion for residual stress for exemption from PWHT.Graphic abstract

Effect of low velocity impact on residual compressive strength of stiffened panel with welding residual stress

Al-Li alloy stiffened panel is the main structural form of aircraft fuselage. Laser welding will produce welding deformation and residual stress, on the other hand, low velocity impact will also affect the residual bearing capacity of stiffened panel structure. In this study, the nonlinear finite element (FE) method is used to simulate the laser welding process of stiffened panel, and the welding residual stress is directly introduced into the subsequent impact after compression (CAI) process of stiffened panel. The effects of different impact positions and different impact energy on the residual CAI strength of stiffened panel are studied. The results show that the impact damage has the greatest effect on the residual compressive strength of stiffened panel when the punch impacts the stiffener, and the greater the impact energy is, the greater the influence is.

Characteristics of welding distortion and residual stresses in thin-walled pipes by solid-shell hybrid modelling and experimental verification

Welding distortion in thin-walled pipes is a prominent and common problem, deteriorating the dimensional accuracy and even increasing the failure risk. The objective of this study is to improve our understanding of welding behaviors and mechanism of thin-walled pipes and thus provide reference for developing control schemes. A solid-shell hybrid model was developed to analyze the characteristics of welding distortion and residual stress distribution with improved modelling and calculation efficiency. The hybrid modeled results agreed well with the experimental measurements and conventional full solid model. It was observed that the welding deformation in seam-welded pipes presents a combined form incorporating convex bending on the circumstance and axial bending toward the weld side besides the shrinkage in both directions. The maximum distortion was observed in the two ends of weld line. Self-restraint characteristics of pipe structures were clarified by analytical solutions to analyze the bending distortions in both hoop and axial directions. For welding residual stresses, the axial stress near the weld line was high tensile stress, and the value on the inner surface was slightly larger than the outer one. The hoop stress near the weld was compressive on the outer surface and tensile on the inner side with similar magnitude. The correlation between welding inherent deformation components and pipe diameter was further clarified using the proposed hybrid model. Effect of shell element percentage and size on simulated results was also discussed to provide a reference for the application of the solid-shell hybrid model.

Effect of weld residual stress on fatigue strength

AbstractResidual stress (RS) refers to the stress permanently present in structures without any external load. This stress can be introduced by different sources, for instance, weld, post‐weld treatment, etc. Weld is a joining process that is associated with intensive heating which leads to considerable change in local material microstructure and the formation of high residual stresses in the welded joint. Residual stress introduces a change in the stress ratio, which means a change in the characteristic of cyclic loading which can have a detrimental effect on the fatigue strength of welded joints. In this paper, an experimental and numerical study of weld residual stress through the thickness direction at the weld toe of transversal attachment made with S355 was investigated. It was found that weld induced compressive residual stress at the surface. In the case where weld induces compressive residual stress, the fatigue life is 4.5 times higher than the standard as‐welded S‐N curve (when tensile residual stress is introduced)

Experimental investigation on microstructure, mechanical properties, and residual stresses of dissimilar welded joint of martensitic P92 and AISI 304L austenitic stainless steel

In this study, microstructural characteristics and mechanical properties of martensitic steel P92 and AISI 304L austenitic stainless steel (ASS) dissimilar metal weld (DMW) have been examined. The welding was performed using the multipass gas tungsten arc welding (GTAW) process. The ERNiCrMo-3 (Inconel 625) filler metal was used due to its excellent compatibility with the P92 and AISI 304L ASS metals. The microstructure characterization performed with an optical microscope and scanning electron microscope revealed the presence of an unmixed zone in the form of beach, peninsula, and island at the base metal and weld fusion zone interface. Secondary phases enriched with Nb and Mo, and migrated grain boundaries (MGBs) were also observed at the weld fusion zone. The microstructural characterization at the P92 side revealed the presence of a soft ferrite zone and delta ferrite at the weld and P92 interface. The different peak temperature experienced by the P92 metal during the welding process results into the formation of three distinct zones with diverse mechanical and microstructural properties namely coarse grain heat affected zone (CGHAZ), fine grain heat affected zone (FGHAZ), and inter-critical heat affected zone (ICHAZ). The post weld heat treatment (PWHT) at 760 °C for 2 h followed by air cooling was performed to homogenize this heterogeneous microstructure formed toward the P92 side. It was observed that this PWHT does not have any significant effect on weld fusion zone and 304L SS heat affected zone (HAZ) microstructure. But, PWHT modifies the microstructure of P92 side HAZ. The tensile test, Vickers micro-hardness test, and charpy impact test were carried out to determine the mechanical properties of the DMW. The tensile strength was found as 587.709 MPa in the as-welded condition and 594.515 MPa in PWHT condition. The tensile test results indicated that specimens were failed from 304L stainless steel (SS) base metal (BM) in as-welded and PWHT condition. The charpy impact toughness test results showed that the toughness of the weld joint was very low in as-welded and PWHT condition (47J) compared to the P92 (190J) and SS 304L (285J) BM. From the microhardness examination, it was observed that the ICHAZ was the weakest zone among all the other regions due to its lower micro-hardness value compared to the other regions. After welding process, residual stresses were measured in as-welded and after PWHT condition at the center of the weld and at the HAZ of P92 and SS 304L (through the thickness of the plate) using experimental-based deep hole-drilling (DHD) strain-gauge method. The results showed that both circumferential (hoop stress) and axial (longitudinal stress) welding residual stresses were decreased after PWHT.

Multi-Objective Optimization of MIG Welding and Preheat Parameters for 6061-T6 Al Alloy T-Joints Using Artificial Neural Networks Based on FEM

To control the welding residual stress and deformation of metal inert gas (MIG) welding, the influence of welding process parameters and preheat parameters (welding speed, heat input, preheat temperature, and preheat area) is discussed, and a prediction model is established to select the optimal combination of process parameters. Thermomechanical numerical analysis was performed to obtain the residual welding deformation and stress according to a 100 × 150 × 50 × 4 mm aluminum alloy 6061-T6 T-joint. Owing to the complexity of the welding process, an optimal Latin hypercube sampling (OLHS) method was adopted for sampling with uniformity and stratification. Analysis of variance (ANOVA) was used to find the influence degree of welding speed (7.5–9 mm/s), heat input (1500–1700 W), preheat temperature (80–125 °C), and preheat area (12–36 mm). The range of research parameters are according to the material, welding method, thickness of the welding plate, and welding procedure specification. Artificial neural network (ANN) and multi-objective particle swarm optimization (MOPSO) was combined to find the effective parameters to minimize welding deformation and stress. The results showed that preheat temperature and welding speed had the greatest effect on the minimization of welding residual deformation and stress, followed by the preheat area, respectively. The Pareto front was obtained by using the MOPSO algorithm with ε-dominance. The welding residual deformation and stress are the minimum at the same time, when the welding parameters are selected as preheating temperature 85 °C and preheating area 12 mm, welding speed is 8.8 mm/s and heat input is 1535 W, respectively. The optimization results were validated by the finite element (FE) method. The error between the FE results and the Pareto optimal compromise solutions is less than 12.5%. The optimum solutions in the Pareto front can be chosen by designers according to actual demand.

Optimized welding process of residual stress control of P91 steel considering martensitic transformation

P91 steel belongs to martensitic heat-resistant steel. Solid phase transformation (SPT) during welding will affect temperature field and stress field. In this paper, a method for calculating welding residual stress of P91 steel considering martensitic transformation is proposed by using finite element (FE) software ABAQUS and self-compiled user subroutines. The methods of reducing residual stress are analyzed through the preheating, changing the starting temperature of martensitic transformation and controlling the interlayer temperature. It is found that the Mises stress decreases and the low stress area at the weld bead enlarges after preheating. Within a certain range, the Mises stress value can be reduced by decreasing the starting temperature of martensitic transformation. The starting temperature of martensitic transformation is suggested to be 325 °C. Within a certain range, increasing interlayer temperature can enlarge the low Mises stress area, increase the longitudinal compressive residual stress and reduce the transverse residual tensile stress. The highest interlayer temperature should not exceed 315 °C.

Effects of laser and GMA hybrid welding parameters on shape, residual stress and deformation of HSLA steel welds

Abstract As a high-efficiency and high-quality welding process, hybrid laser-MAG welding (HLMW) has significant potential of application in welding thick plates. In the present study, based on thermal elastic–plastic theory, a three-dimensional finite element model is developed to predict the weld shape characteristics, residual stress and distortion in HLMW for a butt joint of 12-mm-thick high strength steel plate. Metal active gas arc welding (MAG) heat input and laser energy are modeled as one double-ellipsoid body heat source and one cone body heat source with enhanced peak density along the central axis, respectively. The comparison between calculated molten pool shapes and those obtained by the experiment shows a good agreement. Then weld shape characteristic, residual stresses and distortions are calculated in four different welding process parameters. The results show that the increase of laser power and current can effectively increase the weld penetration width when the welding speed is fixed. At the top surfaces of weldment, the peak stress of high laser beam power is more significant than that of low laser beam power. A high compressive transverse stress of low laser beam power can be found at the welding zone and the surrounding heat affected zone. However, at the bottom surfaces of weldment, the peak stress of low laser beam power is larger than that of high laser beam power. The peak stress of low laser beam power is much larger than that of high laser beam power. A high compressive transverse stress of low laser beam power can be found at the welding zone. The vertical deformation in low laser beam power and low arc current welding has the lowest value.

Experimental Characterisation and Numerical Modelling of Residual Stresses in a Nuclear Safe-End Dissimilar Metal Weld Joint

In this study, a mock-up of a nuclear safe-end dissimilar metal weld (DMW) joint (SA508-3/316L) was manufactured. The manufacturing process involved cladding and buttering of the ferritic steel tube (SA508-3). It was then subjected to a stress relief heat treatment before being girth welded together with the stainless steel tube (316L). The finished mock-up was subsequently machined to its final dimension. The weld residual stresses were thoroughly characterised using neutron diffraction and the contour method. A detailed finite element (FE) modelling exercise was also carried out for the prediction of the weld residual stresses resulting from the manufacturing processes of the DMW joint. Both the experimental and numerical results showed high levels of tensile residual stresses predominantly in the hoop direction of the weld joint in its final machined condition, tending towards the OD surface. The maximum hoop residual stress determined by the contour method was 500 MPa, which compared very well with the FE prediction of 467.7 Mpa. Along the neutron scan line at the OD subsurface across the weld joint, both the contour method and the FE modelling gave maximum hoop residual stress near the weld fusion line on the 316L side at 388.2 and 453.2 Mpa respectively, whereas the neutron diffraction measured a similar value of 480.6 Mpa in the buttering zone near the SA508-3 side. The results of this research thus demonstrated the reasonable consistency of the three techniques employed in revealing the level and distribution of the residual stresses in the DMW joint for nuclear applications.

Influence of Residual Stresses on the Weld Metal Hardness of 5V Titanium Alloy

Influence of residual welding stresses on the hardness values of the weld metal is studied. The investigations were carried out on 5V titanium alloy welded joints, obtained by electron-beam welding and argon-arc welding (TIG-welding). It is shown that the nature of the residual stresses distribution depends on the parameters of welding and affects the hardness values of the weld metal. It is shown, that the difference between the hardness values of the metal after welding and the metal after partial relief of residual stresses on the investigated alloy is up to 90 MPa, which is about 3% of the weld metal hardness level.