Welding Residual Stress Research Articles

Effects of Different Pre-Heating Welding Methods on the Temperature Field, Residual Stress and Deformation of a Q345C Steel Butt-Welded Joint

Heavy plate welding has been widely used in the construction of large projects and structures, in which the residual stress and deformation caused by the welding process are the key problems to address to reduce the stability and safety of the whole structure. Strengthening before welding is an important method to reduce the temperature gradient, control the residual stress and reduce the deformation of welds. Based on the ABAQUS software, the thermal elastoplastic finite element method (FEM) was used to simulate the welding thermal cycle, residual stress and deformation of low-alloy, high-strength steel joints. Based on the finite element simulation, the influences of flame heating and ceramic heating on the temperature field, residual stress distribution and deformation of a Q345C steel butt-welded joint were studied. The results showed that the thermal cycle of the ceramic sheet before welding had little influence on the whole weldment, but had great influence on the residual stress of the weldment. The results show that the maximum temperature and residual stress of the welded parts are obviously weakened under the heating of ceramic pieces, and the residual stress of the selected feature points is reduced by 5.88%, and the maximum temperature of the thermal cycle curve is reduced by 22.67%. At the same time, it was concluded that the weld shapes of the two were basically the same, but the weld seams heated by ceramic pieces had a better weld quality and microstructures through comparing the macro- and micro-structures between the welded parts heated by ceramic pieces and the simulated weld. Heating before welding, therefore, is an effective method to obtain a high weld quality with less residual stress and deformation.

Numerical simulation of crack in a residual stress field

Fracture mechanics analysis of metallic material is unequivocally one of the principal areas in the study of the failure of materials. The effect of residual stress on failure is often overlooked and usually not considered during the design stage. However, residual stress plays a crucial role in determining the failure of materials. This work studies the behaviour of a crack in a residual stress field. A residual stress field in a welded plate is obtained by finite element simulation of fusion welding. Subsequently, a stationary crack is introduced in the welded plate. J-integral is used to characterize the crack behaviour. The variation in J-integral values with the welding residual stress is studied. It is observed that crack behaviour and stress distribution in a residual stress field depend on the magnitude of primary stress in the material.

Residual stresses in austenitic thin-walled pipe girth welds: Manufacture and measurements

Determining residual stresses in thin-walled pipes is challenging. They are potentially difficult targets for simulation, because they may not behave as simple axisymmetric structures during welding. Thin-walled pipes are more sensitive to changes in the welding heat input than thick-walled pipes. They are also under-represented in the existing population of residual stress measurements used to generate upper bound residual stress profiles for structural integrity assessments. In this paper, residual stress characterisation of two thin-walled austenitic girth welded pipes is presented. The overall geometries of the two mock-up designs were the same; they differed in the linear heat input per pass and the total number of weld passes. The residual stress characterisation was carried out using two independent measurement techniques; the contour method and neutron diffraction. The multiple-cut contour strategy was implemented to measure the cross-sectional maps of hoop and axial stresses on axial-radial and hoop-radial planes respectively. The contour method results are compared with stresses measured using neutron diffraction and specific residual stress distribution signatures observed are discussed.

Effects of non-symmetric non-uniformly distributed welding residual stress on fatigue failure initiation and propagation in a hydropower generator shaft

PurposeThis article aims to investigate and model the effects of welding-generated thermal cycle on the resulting residual stress distribution and its role in the initiation and propagation of fatigue failure in thick shaft sections.Design/methodology/approachExperimental and numerical techniques were applied in the present study to explore the relationship(s) between welding residual-stress distribution and fatigue failure characteristics in a hydropower generator shaft. Experimental techniques included stereomicroscopy, optical and scanning electron microscopy (SEM), chemical analysis and mechanical testing. Finite element modelling (FEM) was used to model the shaft welding cycle in terms of thermal (temperature) history and the associated development of residual stresses within the weld joint.FindingsExperimental analyses have confirmed the suitability of the used material for the intended application and confirmed the failure mode to be low cycle fatigue. The observed failure characteristics, however, did not match with the applied loading in terms of design stress levels, directionality and expected crack imitation site(s). FEM results have revealed the presence of a sharp stress peak in excess of 630 MPa (about 74% of material's yield strength) around weld start point and a non-uniform residual stress distribution in both the circumferential and through-thickness directions. The present results have shown very close matching between FEM results and observed failure characteristics.Practical implicationsThe present article considers an actual industrial case of a hydropower generator shaft failure. Present results are valuable in providing insight information regarding such failures as well as some preventive design and fabrication measures for the hydropower and other power generation and transmission sector.Originality/valueThe presence of the aforementioned stress peak around welding start/end location and the non-uniform distribution of residual-stress field are in contrast to almost all published results based on some uniformity assumptions. The present FEM results were, however, the only stress distribution scenario capable of explaining the failure considered in the present research.

Numerical Strength Analysis of Laser-Welded Differential Housing and Gear Considering Residual Stress.

In order to avoid slackening of differential housing and gear joined by bolts, the laser-welding process is proposed in this paper, and the strength of a connecting joint was estimated by numerical analysis with consideration of welding residual stress. The process parameters of laser welding for dissimilar materials QT600 cast iron and 20MnCr5 structural alloy steel were introduced, and chemical composition analysis and microstructure analysis were conducted on the welded joints. The finite element model of laser-welded differential housing and gear was established to obtain the welding residual stress by applying a moving heat source. To verify the accuracy of the simulated result, static pressing tests were employed. The maximum tensile residual stress was 319.4 MPa, located at the same point as the maximum temperature. The simulated stress agreed well with the experimental data. Finally, the dynamic strength of laser-welded differential housing and gear under forward, reverse, and start-up conditions was assessed by regarding welding residual stress as the initial stress field, which showed that all safety factors were greater than 1.4.

Influence of preheating on residual stresses in ultra-high strength steel welded components

Preheating is generally required in the welding of ultra-high strength steels (UHSSs) for avoiding cold cracking. The present work systematically explores the influence of preheating on welding residual stresses (WRS) in components made of UHSS by means of both experiments and numerical simulations. The results reveal that, no matter what UHSS is with or without metallurgical phase transformation, preheating has a great influence on the magnitude of transverse residual stress (σT-RS). In general, the higher preheating temperature (TPH) the lower magnitude of σT-RS is. Preheating would change the longitudinal residual stress (σL-RS) sign in the weld area and σL-RS amount obviously diminishes with the increase of TPH for transforming UHSS, while that has nearly no influence on the maximum σL-RS but has an impact on the area of tensile σL-RS for non-transforming UHSS. The effect of entire preheating and partial preheating on WRS in UHSS welded components could be nearly the same. Nevertheless, TPH in the partial preheating case (about 300 °C here) should be higher than that in the entire preheating one (corresponding 100 °C here) for that same effect. The weld dimensions, especially the size of the heat-affected zone (HAZ), and cooling time Δt8/5 significantly increase with TPH. Preheating has almost no influence on the restraint degree of welded components.

Influence of initial residual stresses on welding residual stresses in ultra-high strength steel S960

In general, the as-received steel components before welding have usually suffered from numerous manufacturing processes. There is no doubt that initial residual stresses (IRS) remain in the steels with different magnitudes and even signs if no any stress-relieving process is applied before welding. Nevertheless, the relationship between IRS and welding residual stresses (WRS) is still not unclear yet, especially in ultra-high strength steels (UHSS). The current work aims to elucidate the influence of IRS on WRS in ultra-high strength steel S960. The X-ray diffraction (XRD) was applied to measure both IRS and WRS here. The experimental results exhibit that IRS in the weld area are completely eliminated because of the metallurgical and mechanical melting effect, which have no influence on WRS. In the heated zone out of the weld area, initial longitudinal residual stress (σRSL) can significantly affect welding σRSLonly if it is in tension. In the cold area, WRS are the combination of IRS and welding-induced residual stresses (WIRS). Furthermore, IRS play the dominant role here in general. No matter how much and what sign IRS are in the cold area, IRS here almost have no impact on WRS in the weld area.

A Uniformed Calculation Criterion on Heat Band Width of Local PWHT on Welded Joint with Dissimilar Thickness

Local post-weld heat treatment is used to reduce welding residual stresses. The existing standards have great differences in the selection of the width of the heated band, and the heating width, as an important control parameter of the local heat treatment, will directly affect the quality of the heat treatment. In this paper, the numerical simulation method is used to simulate the welding and heat treatment process of unequal-thickness joints. The stress and deformation of the joint with different thickness ratios under different heating widths are studied by finite element simulation, focusing on the influence of the width of the heated band on the residual stress relief of the joint. Based on these studies, the criteria for determining the optimal width of the heating zone are consistent. Finally, the formula HB=HB1+HB2=3RT+1+k2RT for calculating local heat treatment heating width based on the thickness of welded joint for SA738Gr.B steel is established. Among them, HB1 is the width of the main heating zone, HB2 is the width of the auxiliary heating zone, k is the thickness ratio of the thick plate to the thin plate, and t is the wall thickness of the thin plate.

Study on the Microstructure and Properties of Welded Joints of Laser Shock Peening on HC420LA Low-Alloy High-Tensile Steel.

Laser shock peening is a promising surface strengthening technology that can effectively improve the mechanical properties of materials. This paper is based on the laser shock peening process for HC420LA low-alloy high-strength steel weldments. Contrast analysis of the evolution of the microstructure, residual stress distribution and mechanical properties of the welded joints before and after the laser shock peening on each region is carried out; a combination of tensile fracture and impact toughness fracture morphology analyses of laser shock peening on the welded joint strength and toughness regulation mechanism are also completed. The results show that the laser shock peening can refine the microstructure of the welded joint effectively, the microhardness of all areas of the joint increases and the weld residual tensile stresses are transformed into beneficial residual compressive stresses, affecting a layer depth of 600 μm. In addition, the strength and impact toughness of welded joints of HC420LA low-alloy high-strength steel are improved.

Grain size and shape dependent crystal plasticity finite element model and its application to electron beam welded SS316L

Electron beam welding is an autogenous welding process that leads to microstructural heterogeneities; crystallographic texture, elongated and larger grain size relative to the surrounding parent material. The goal of this study is to predict the changes in mechanical response of the weld fusion zone as a function of grain morphology and texture by using the parent material properties to avoid extensive and costly experimental campaigns. For this reason, a crystal plasticity solver, “University of BRIstol cryStal plasTicity sOLver” (BRISTOL), is implemented in a finite element framework with new constitutive laws to account for the length-scale dependence considering the size and shape of the grains. It is found that the crystallographic texture governs the orientation specific elastic stiffness and yield stress having the most dominant effect on the macroscopic response of the weldment at the grain size scales considered. Crucially the length-scale dependent model allows accurate prediction of the yield strength of the weldment over a range of microstructures, also highlighting the presence of other factors such as prior strain hardening during the welding process and residual stresses.

The Different Welding Layers and Heat Source Energy on Residual Stresses in Swing Arc Narrow Gap MAG Welding.

In this paper, in order to reduce the time cost of prediction experiments in industry, a new narrow gap oscillation calculation method is developed in ABAQUS thermomechanical coupling analysis to study the distribution trend of residual weld stresses in comparison with conventional multi-layer welding processes. The blind hole detection technique and thermocouple measurement method verify the reliability of the prediction experiment. The results show that the experimental and simulation results have a high degree of agreement. In the prediction experiments, the calculation time of the high-energy single-layer welding experiments is 1/4 of the traditional multi-layer welding. Two welding processes of longitudinal residual stress and transverse residual stress distribution trends are the same. The high-energy single-layer welding experiment stress distribution range and transverse residual stress peak are smaller, but the longitudinal residual stress peak is slightly higher, which can be effectively reduced by increasing the preheating temperature of the welded parts. This implies that in the specific case of increasing the initial temperature of the workpiece, the use of high-energy single-layer welding instead of multi-layer welding to study the residual stress distribution trend not only optimizes the weld quality but also reduces the time cost to a large extent.

Study on the relationship between the root welding residual stress and the root-failure fatigue strength of Plug Welded specimens

It is difficult to examine the relation between the root notch welding residual stress (WRS) and the root-failure fatigue strength because of the difficulty in the direct root WRS measurement. The root WRS can be calculated by thermal elastic-plastic finite element analysis (TEPFEA), but its accuracy has not been fully verified yet. In this study, root-failure fatigue tests, in which direct root WRS measurement can be performed, are carried out. Plug welded (PW) specimens with backing plates are used in those tests, and the root WRS in as-welded (AW) and stress-relieved (SR = PWHT) specimens are measured using X-ray diffraction (XRD) method by cutting off the backing plate. The measured WRSs are compared with those calculated by TEPFEA. It is found that the root WRSs in the PW specimens estimated by TEPFEA become much larger than those measured when creep strain is neglected. The SR specimen’s fatigue strength improvement ratio is estimated by using the mean stress effect formulas developed for toe-failure cases (IIW Fatigue Recommendations and MIL-HDBK-5D). The estimated improvement ratio shows fair agreement with that measured.

Simulation and experiment on residual stress and deflection of cruciform welded joints

Numerous engineering components and structures require welding, including ships, automobiles, and many other manufactured products. Distortions and residual stresses created in welded joints can lead to adverse and destructive effects on structural integrity, service life, and visual appearance, and can produce significant dimensional inaccuracies. The ability to predict these effects accurately is, therefore, crucial for ensuring weld functionality and long service life. This study aims to examine the characteristics of welding deformation and residual stress in cruciform fillet welded joints using the FE software Simufact Welding. In the work, experimental measurements of temperature, deflection, and residual stress were used to verify the simulation models. The effect of plate thickness and welding sequence on welding deformation was examined through numerical simulations and experimental work. Additionally, the cause of angular distortion was explained using an FE model. An X-ray diffraction technique was adopted to record residual stress levels for the cruciform fillet welded joints. Reasonable agreement was found between the experimental measurements and the results obtained from the simulations.

Influence of welding residual stress on bending resistance of hollow spherical joints

Welded hollow spherical joints are widely used in large-span spatial structures because of their simple organization and convenient construction. However, in the sphere-pipe connection welds of the joints, welding residual stress is generated, which will adversely affect the mechanical properties of the joints and the overall structure. In this paper, the parametric model of welded hollow spherical joints was established by employing the geometric configuration dimensions of those joints frequently used in engineering. Through the combination of experimental research and numerical simulation, the welding residual stress of welded hollow spherical joints and its impact on joints' bending resistance were studied. First of all, based on the distribution pattern of the stress, bending test of the joints was carried out and revealed the influence of welding residual stress on the bending stiffness and ultimate bending capacity of the joints; Then, through the results of experimental analysis and finite element calculation, and with parametric analysis, the impact of welding residual stress on joints' bending resistance was clarified with the variation of parameters such as the hollow sphere diameter D, wall thickness t and the connecting steel pipe diameter d. It is shown that welding residual stress has a great impact on joints' bending stiffness, with a reduction more than 10%, while it doesn't affect their ultimate bending capacity much, with an influence no more than 5%. In addition, as D increases, t, and d decrease, its impact on the bending resistance rises.

Welding Residual Stress Elimination Technique in the Top Chord of Main Truss of Steel Truss Bridge

The large-amplitude fluctuations of ultrasound in high-energy ultrasonic stress relieving cause the crystal grains or lattices in the high residual stress zone to vibrate or creep alternately. This triggers secondary effects such as ultrasonic softening and dislocation movement. The sound field also produces periodic shock waves or intermittent shock waves, which form local pressure gradients at the wave front. These pressure gradients cause local heating of the grain boundary, accelerating material softening and promoting slip between grains, ultimately resulting in residual stress elimination. This technique was applied to detect the welding residual stress of the upper chord of the main truss of Sanguantang Bridge by using an ultrasonic stress meter. After the measurement, it was found that the welding residual stress in some areas was too large, and the welding residual stress needed to be eliminated. The welding seam was re-inspected after the residual stress relief operation was completed. The test results showed a maximum reduction rate of 63.91% and an average overall reduction rate ranging from 24.52% to 37.23%. The reduction effect is more significant in areas with higher welding residual stress.

Influence of distortion ratio on distortion-induced fatigue behavior of steel girder bridges

The physical fatigue test and a new proposed research methodology called the digital fatigue test are used to investigate distortion-induced fatigue performance at web gap regions in steel girder bridges. Digital fatigue test based on the extended finite element method can combine factors such as residual welding stress, initial defects, and fatigue action, to simulate the propagation of mixed-mode cracks. Physical and digital fatigue test results show fatigue strength decreases significantly with increasing distortion ratio, which is the ratio of the minimum and maximum distortion at web gaps. When distortion ratio and nominal stress ratio increased from 0.2 to 0.5, the fatigue strength of 60 mm horizontal gusset plate–vertical​ stiffener web gap and 40 mm vertical stiffener web gap decreases by 43% and 50%, respectively.

Influence of Heat Input on Microstructure and Mechanical Properties of Laser Welding GH4169 Bolt Assembly—Numerical and Experimental Analysis

By conducting the numerical and experimental analysis, the influence of heat input on the microstructures and mechanical properties of laser welding GH4169 bolt assembly is systematically investigated. The weld formation, temperature field, and residual stress distribution during laser welding by using the finite element modeling are consistent with experimental results. The numerical simulation results show that the increase of heat input imparts lower residual stresses and higher temperature gradient. During the process of laser welding, the steepest temperature gradient and the peak residual stress arise in the fusion zone (FZ). In addition, the dissolution of γ″ and γ′ toward the fusion line increases in heat affected zone (HAZ), but only Laves phase is observed in FZ. With increasing heat input from 24 to 48 J mm−1, the ultimate tensile strength of welded joints decreases. Both the lowest microhardness values and tensile failure of GH4169 alloy laser welded joint are in FZ. Herein, it is that the relationship among the heat input, microstructures, and mechanical properties of GH4196 bolt assembly in laser welding is systematically established, which will be of guiding significance for the selection of welding parameters in aerospace.

Investigation on residual stress of EQ56 high strength steel butt weld

In the welding process of high-strength steel (HSS), the intense temperature change in joints induces the formation of welding residual stress (WRS), which increases the fatigue crack growth rate. Developing an effective finite element (FE) model for accurately predicting the WRS distribution is critical to improve the quality of welded structures. Experimental tests and numerical simulations were carried out to investigate the WRS distribution of EQ56 HSS. The thermal expansion curves at various heating and cooling rates were measured through thermal simulation experiments for achieving the continuous cooling transformation (CCT) diagram of EQ56 HSS. Based on the CCT diagram, the thermo-metallurgical-mechanical (TMM) FE model was developed to consider the influence of solid-state phase transformation (SSPT) on distribution and magnitude of WRS for welded EQ56 HSS joints, as well as material hardening law. Comparison of predicted WRS distribution and experimental data shows that plastic hardening laws of materials significantly affect the precision of WRS distribution, and combined hardening law gives most reliable prediction. The FE model considering SSPT behavior provides more accurate estimation of WRS distribution than those without considering SSPT behavior.

Fatigue Life and Crack Initiation in Monopile Foundation by Fatigue FE Analysis

The construction of new renewable energy infrastructures and the development of new ocean resources continues to proceed apace. In this regard, the increasing size and capacity of offshore wind turbines demands that the size of their accompanying supporting marine structures likewise increase. The types of marine structures utilized for these offshore applications include gravity base, monopile, jacket, and tripod structures. Of these four types, monopile structures are widely used, given that they are comparatively easy to construct and more economical than other structures. However, constant exposure to harsh cyclic environmental loads can cause material deterioration or the initiation of fatigue cracks, which can then lead to catastrophic failures. In this paper, a 3D fatigue finite element analysis was performed to predict both the fatigue life and the crack initiation of a welded monopile substructure. The whole analysis was undertaken in three steps. First, a 3D non-steady heat conduction analysis was used to calculate the thermal history. Second, a thermal load was induced, as an input in 3D elastoplastic analysis, in order to determine welding residual stresses and welding deformation. Finally, the plastic strain and residual stress were used as inputs in a 3D fatigue FE analysis in order to calculate fatigue crack initiation and fatigue life. The 3D fatigue finite element analysis was based on continuum damage mechanics (CDM) and elastoplastic constitutive equations. The results obtained from the 3D fatigue finite element analysis were compared with hot spot stresses and Det Norske Veritas (DNV-GL) standards.

Cyclic elastoplasticity-based life assessment of fatigue crack initiation and subsequent propagation in rib-to-deck welded joints

Conventional S-N curve methods for fatigue life assessment fail to consider the different cracking mechanisms of crack initiation and propagation, resulting in less accurate predictions of fatigue life. The present study aims to assess the fatigue crack initiation and subsequent propagation life of rib-to-deck welded joints separately by accurate prediction of local cyclic elastoplasticity. The welding residual stress was simulated with high precision by thermal-mechanical analysis based on the real bead geometry and welding parameters, and defined as initial stress condition. The performance of an unconventional Fatigue Subloading Surface constitutive model (FSS model, hereafter) to predict the cyclic elastoplasticity in the sub-yield stress state was proved by comparing to the experiment results and conventional plasticity theory. The FSS model was then embedded to distinct zones of welded joints for cyclic structural analyses. Considering the relaxation of residual stress, the fatigue crack initiation by the local strain approach based on the local cumulative plasticity damage, and propagation life was assessed by the analytical approach based on the LEFM parameters of materials. As a connection between the crack initiation and propagation, the initial crack featured by 0.5 mm depth and semi-circular shape was proposed. The current work is verified to assess the fatigue life of rib-to-deck welded joints with high accuracy under the pure bending load against experiment results.