Residual Stresses In Welded Joints Research Articles

Study on relieving residual stress of friction stir welded joint of 2219 aluminum alloy using cold spraying

Friction stir welding is an advanced solid state welding technology, which has been widely used in aerospace and other fields. However, the large tensile residual stress developed in such joints will significantly affect mechanical properties. Cold spraying, as a new method to reduce residual stress of welded joints, can also improve the mechanical properties of the joints. In this paper, the correlation between microstructure and mechanical properties and residual stress of 2219 aluminum alloy joints prior and after coated with cold spraying was studied with experiments and numerical simulation for a 4 mm thick joint. The primary mechanism of stress relief of the joint was identified. Results show the refinement of grain size, with grain size decreasing from 2.1 μm in welded joints to 0.7 μm of cold sprayed joints, while high angle grain boundaries increase from 38.0% in the welded joint to 62.7% in cold sprayed ones. The ratio of recrystallized grains in the joints increases from 19.1% to 46.9%, while the joint strengthening phases θ″ and θ' increase, which increases tensile strength of the joints from 343 MPa to 398 MPa. The elongation is increased from 4.5% to 10.2%, and the average hardness of the joint is increased by 35 HV. The “ shot peening effect “ of cold spraying is found to be the primary factor to reduce residual stresses, while the “ heat flow effect “ has negligible effect on stress reduction. The mechanism of reducing residual stresses is provided by the macroscopic stress-strain theory and the microscopic dislocation theory.

Nondestructive evaluation of residual stresses in welded joints on the base of a combination of ultrasonic testing and speckle-interferometry

Nondestructive evaluation of residual stresses in welded joints on the base of a combination of ultrasonic testing and speckle-interferometry

Thermo-Mechanical Study of TIG Welding of Ti-6Al-4V for Residual Stresses Considering Solid State Phase Transformation

To overcome the detrimental effect of residual stress in welded joints, which affects the overall performance of the welded structure, this paper studies the magnitude and distribution of residual stress after welding and local post-weld heat treatment (PWHT). The coupled thermo-metallurgical-mechanical model for welding 6 mm thick Ti-6Al-4V (TC4) titanium alloy plates was established, the evolution of the SSPT and its effect on the residual stress were quantitatively analyzed, and a parametric analysis of local PWHT was performed. The results demonstrated that there was good agreement between the numerical results and the experimental data. Due to the cooling rate reaching 327 °C/s, the volume fraction of α、 in the fusion zone (FZ) reached 0.218 after welding and decreased by 90.83% after PWHT when the heating temperature was 700 °C. The peak value of the longitudinal residual stress can reach 686.4 MPa after welding with SSPT, which was 11.38% lower than that without SSPT, and it decreased by 65.6% after PWHT when the heating temperature was 900 °C. The research results demonstrate that SSPT has a significant effect on residual stress, and PWHT can obviously reduce the residual stress, which provides a certain reference for welding TC4 titanium alloy plates.

Mitigation of Porosity and Residual Stress on Carbody Aluminum Alloy Vibration Welding: A Systematic Literature Review

Fatigue resistance is influenced by porosity and residual stress in welded joints. Fatigue failure in some means of transportation is caused by the inability to withstand the load received from the car body and passengers while operating. This study uses a systematic literature review (SLR) method to identify the effect of vibration welding on porosity and residual stress. Vibration can reduce the empty cavity (porosity) and increase the density of the weld. The ultrasonic vibration spot resistance (UVSR) method with 20 kHz on AA6082 is able to reduce residual stress up to 53% and is effective for homogenization of concentrated residual stress up to 57%.

Study on Susceptibility and Mechanism of Reheat Cracking in Welded Joint of Type 347 Austenitic Stainless Steel

The reheat cracking susceptibility of welded joints has been evaluated by 900°C high-temperature constant load test and 750°C–900°C high-temperature slow strain rate tensile (SSRT) test on welded joints of TP347 steel, and the influencing factors and mechanism of reheat cracking in welded joints have been further investigated by microcosmic characterization techniques of SEM and EDS, etc. The result shows the critical fracture stress of TP347 steel welded joints at 900°C is 24 MPa, which is much lower than 80% of the high-temperature yield strength of base material, indicating that the reheat crack of the welded joint is highly sensitive at this temperature; the average reduction of area (RoA) of welded joints obtained by 750°C–900°C SSRT test at each temperature is below 20%, which means all welded joints have a reheat cracking susceptibility in this temperature range, and the reheat cracking susceptibility increases with the rising of temperature. Based on study and analysis using microcosmic methods of optical microscope, scanning electron microscope, and energy spectrum analysis, it is found that welded joints of TP347 steel have a high reheat cracking susceptibility because the high temperature accelerates the diffusion of Cr, Nb, and impurity elements to the grain boundary, and a large quantity of carbides and low-melting-point eutectics are collected and precipitated at the grain boundary to reduce the plasticity of the grain boundary. Since there is a high welding residual stress in welded joints, cavities are formed under the action of the stress at a high temperature, and the merging of cavities causes the formation of cracks which extend along the grain boundary.

Numerical investigation of residual stresses in welded joints of cylindrical shell

Welded cylinder structures such as pressure vessels and pipes for transportation have been applied in power stations, aerospace, and shipping industries. The study of weld-induced residual stress is vital in predicting the life of welded cylinder vessels. Depending upon the required diameter and length, they are welded by either circumferential welding or longitudinal welding. In the present work, a sequentially coupled thermal, structural analysis is carried out on circumferential and longitudinal butt weld joints of AH-36 cylinder components. The thermal field distribution and subsequent residual stresses during Gas Tungsten Arc Welding (GTAW) are studied. The moving heat source considered for analysis is based upon Goldak’s double ellipsoidal model. The weld-induced axial and hoop stresses are evaluated on both the outer and inner surfaces of the cylinder. The results for circumferential and longitudinal butt weld joints are compared. The magnitude of peak hoop and axial stresses in longitudinal butt weld joints are 45% and 95% higher than in circumferential butt weld joints. The developed analysis model, used to evaluate the thermal histories and residual stresses, is validated with experimental measurements.

Post-weld cold working for fatigue strength improvement of resistance spot welded joint of advanced high-strength steel

Advanced high-strength steel (AHSS) has been widely used for lightweight body-in-white. However, the fatigue strength of welded joints is not improved even employed AHSS. In this research, the advanced post-weld cold working (PWCW) experiment was proposed to improve the fatigue strength of DP980 spot welded joints. X-ray diffraction (XRD) method was employed to measure the welding residual stress. A numerical model was established to analyze the PWCW induced residual stress as the first try. The influence of the diameter of the cylindric tool used in PWCW on the residual stress of welded joints was also discussed in detail. The hardness distribution on weld joint was increased after PWCW, which represented the plastic strain induced work hardening in DP980 steel. The predicted PWCW induced residual stress had a reasonable agreement with XRD measurement. The PWCW introduced a compressive stress in the weld nugget and its heat affected zone with a value of more than -400 MPa at the edge of joined zone. The strengthened material and compressive stress were beneficial to suppress the generation and propagation of fatigue crack, thereby enhance the fatigue strength of welded joints. Besides, the effect of PWCW continuously strengthened with a larger diameter of tool, especially when the tool diameter was larger than 10 mm. The fatigue strength was almost doubled compared with the as-welded condition. The smaller tool provided a critical requirement for precise positioning. The operation of PWCW was also simple enough to realize the automation, which indicated its potential in manufacturing automotive units.

Effect of Yield Strength Distribution Welded Joint on Crack Propagation Path and Crack Mechanical Tip Field.

Due to the particularity of welding processes, the mechanical properties of welded joint materials, especially the yield strength, are unevenly distributed, and there are also a large number of micro cracks, which seriously affects the safety performance of welded joints. In this study, to analyze the effect of the uneven distribution of yield strength on the crack propagation path of welded joints, other mechanical properties and residual stresses of welded joints are ignored. In the ABAQUS 6.14 finite element software, the user-defined field (USDFLD) subroutine is used to define the unevenly distributed yield strength, and extended finite element (XFEM) is used to simulate crack propagation. In addition, the static crack finite element model of the welded joint model is established according to the crack propagation path, which is given the static crack model constant stress intensity factor load, and the influence of an uneven yield strength distribution on mechanical field is analyzed. The results show that the crack length of welded joints as well as the plastic deformation range of the crack tip in high stress areas can be reduced with the increase of yield strength along the crack propagation direction. Moreover, the crack deflects to the low yield strength side. This study provides an analytical reference for the crack path prediction of welded joints.

Numerical simulation of the effect of ultrasonic impact treatment on welding residual stress

Ultrasonic impact treatment (UIT) is an effective method that has been widely applied in welding structure to improve the fatigue properties of materials. It combines mechanical impact and ultrasonic vibration to produce plastic deformation on the weld joints surface, which introduces beneficial compressive residual stress distribution. To evaluate the effect of UIT technology on alleviating the residual stress of welded joints, a novel numerical analysis method based on the inherent strain theory is proposed to simulate the stress superposition of welding and subsequent UIT process of 304 stainless steel. Meanwhile, the experiment according to the process was carried out to verify the simulation of residual stress values before and after UIT. By the results, optimization of UIT application could effectively reduce the residual stress concentration after welding process. Residual tensile stress of welded joints after UIT is transformed into residual compressive stress. UIT formed a residual compressive stress layer with a thickness of about 0.13 mm on the plate. The numerical simulation results are consistent with the experimental results. The work in this paper could provide theoretical basis and technical support for the reasonable evaluation of the ultrasonic impact on residual stress elimination and mechanical properties improvement of welded joints.

ОСОБЕННОСТИ РЕМОНТА СВАРНЫХ КОНСТРУКЦИЙ БОЛЬШИХ ТОЛЩИН ИЗ ТИТАНОВОГО СПЛАВА ВТ6ч.

The technology of electron-beam welding (EBW) of structures of large thickness made of titanium alloy Ti–6Al–4V has been developed. A complex of metallographic studies of welded samples has been carried out. Tests to determine the mechanical characteristics of repair welded joints, that these joints made by EBW are equal in strength to the base material. The analysis of the level of residual stresses in various parts of the welded joint after repeated repair passes has been carried out. It was found that the subsequent vacuum annealing reduces the level of residual stresses in welded joints to 50 %. The analysis of the elemental composition showed that the elemental composition of the samples from the center of the weld to the base metal practically does not change for welding with the number of repeated passes up to 3.

Experimental and numerical study to minimize the residual stresses in welding of 6082-T6 aluminum alloy

One of the most important negative consequence in the fusion welding processes is the generation of tensile residual stresses in welded joints. The main goals of this work are to determine the optimal combination of welding parameters to minimize the residual stress level and the influence of each welding parameter in that feature to weld 6082-T6 aluminum alloy plates using the GMAW welding process. To achieve these goals was implemented the Taguchi orthogonal array (L27) to define the design of numerical and experimental tests. All combinations were simulated in the Simufactwelding 6.0 software, from which it was possible to obtain the values of maximum residual stresses. The data treatment was carried out, reaching the combination of levels for each parameter. With ANOVA analysis was found that the parameter with the greatest influence in the residual stress generation was the welding speed, while the parameter with the least influence was the torch angle. Also, to minimize the residual stresses it was observed that the optimal combination of welding parameters is welding current intensity of 202 A, welding speed of 10 mm/s, and 30° of inclination of the angular torch. The two simulations that resulted in the highest and lowest residual stresses were validated experimentally by the hole drilling method to measure the residual stresses.

Структурно-фазовое состояние и остаточные напряжения в сварном соединении сплава ВТ20, полученном электронно-лучевой сваркой

Структурно-фазовое состояние и остаточные напряжения в сварном соединении сплава ВТ20, полученном электронно-лучевой сваркой

Recommendations for the measurement of residual stresses in welded joints by means of X-ray diffraction\u2014results of the WG6-RR test

Residual stresses in welded joints are often of extended interest in order to evaluate unexpected failures or distortions. Since the possibilities to calculate residual stresses in welds are still strongly limited, the measurement techniques are still of great importance. Several measurement techniques with particular possibilities and limitations are available today where especially the different diffraction methods are used mostly. The material, weld type, and the size of the components are important for the quality of the results obtained with different methods as well as the environment where the measurements have to be carried out. The paper shall give an overview of the results of a round robin test on the application of XRD on butt welded joints which has been carried out in cooperation of different experienced laboratories. The results show the high reliability of XRD measurements in welds, if the measurements are performed under well-defined boundary conditions. The experiences can be used as a recommendation about useful measurement conditions the expectable quality of the results.

Residual stress estimation in defect assessment procedures at weld toe and away locations on girth welds: Review of key parameters

The distribution of residual stresses in welded joints plays an important role within the fracture evaluation guidelines recommended in structural integrity assessment codes such as BS7910, API 579 RP-1/ASME FFS-1 and R6. The residual stress profile recommendations in these standards are based on extensive experimental results and finite element modelling (FEM) based parametric residual stress evaluations at the weld centerline and weld toe positions. The upper bound residual stresses’ profiles based on these recommendations vary significantly from one type of welding process to another for a given weld configuration with identical welding conditions. These fitness-for-service codes (FFS) depict great variability in estimating residual stress profiles during defect assessment, as BS 7910 & R6 recommends a constant profile at a distance away from welds and API 579 provides a single curve for all locations in the axial direction. Thus, conservatism is widely associated with these recommended profiles in fracture potential evaluation and assessments, leading to suboptimal recommendations. In this manuscript, a detailed review is undertaken of residual stress estimation in various FFS codes, showing vast variability among them for locations away from the weld toe on girth welds. Key distinct parameter characteristics, pipe radius to thickness ratio and heat input are detailed and found to have a significant effect on residual stress profiles in structural integrity assessment, using a stress decomposition technique. These recommendations establish an overall analysis of the interrelationship between key parameters, considering a generalized broad range of applications. A framework is proposed, based on the current review, for conducting detailed investigation by employing thermomechanical numerical modelling, coupled with measurement results (nondestructive and semi-destructive) from an experimental study, as input to machine-learning algorithms for application guidance to engineers.

Recent Applications of Residual Stress Measurement Techniques for FSW Joints: A Review

Quality control of welding processes plays a significant role in characterizing of the weld quality. Various Non-Destructive Method (NDM), Semi-Destructive Method (SDM) and Destructive Method (DM) are all employed for welding inspection and quality control. This paper presents a review of the recent research onthe quality control of Friction Stir Welding (FSW) processes of similar and dissimilar alloys. Based on previews articles, this paper focuses on comparing various inspection techniques with the effect of different FSW parameters such as; tilt angle (deg°), rotation speed (rpm), welding speed (mm/min) and axial applied force (N)on the formation or residual stresses across welded joints. Additionally, the inspection measuring parameters, machine used, and material specification are also discussed. Recent studies are classified based on the measuring approach. The key findings for each inspection method are also presented. Researchers report that NDM, SMD and DM greatly contribute in detecting residual stresses of welded joints. However, some techniques like Deep-hole drilling technique have not been extensively applied for quality inspection of the FSW process. This paper reviews the various testing techniques for the FSW, aiming to let more experts know the current research status and also provide some guidance for future research.

Effects of rail flash-butt welding and post-weld heat treatment processes meeting different national standards on residual stresses of welded joints

AbstractThis study investigates residual stresses of the welded joint heat-affected zone for the processes that meet the Chinese and European standards of field rail welding. Furthermore, this study investigates the factory rail welding process and different normalizing methods in China. According to the residual stresses data and the Debye ring test result, the residual stresses distribution of the welded joint meets the Chinese standard and uses induction normalizing treatment resulting in the best service performance and an improvement in grain size uniformity. In the absence of a normalizing process, the ideal welding process that meets the Chinese standard is actually inferior to that which meets the European standard, with regard to a uniform distribution of the residual stresses of the welded joint.

Finite-element inverse analysis of residual stress for laser welding based on a contour method

The thermal effect of laser welding degrades the local material properties, and this inevitably leads to thermal deformation and thermal residual stress in welded joints. In this study, the residual stress distribution of laser-welded Al–Li alloy parts was measured by a combination of the contour method and finite-element simulation. First, the contour deformation of the cutting surfaces of welded parts resulting from the release of residual stress was measured by a coordinator. Then, the reverse contour deformation was applied to the finite-element model as the displacement boundary condition to invert the full-field residual stress of the cutting surface. Furthermore, a thermal/structural sequential coupling analysis method was used to establish a complete three-dimensional finite-element model of a laser-welded plate and calculate the residual stress field, taking the actual weld morphology as the characteristic parameter of the heat source, using the improved conical heat source model of laser welding. The result is consistent with the results of the contour method.

A design method of tensile triangles and low transformation temperature weld metal for reduction of stress concentration and residual stress of welded joints

Stress concentration and residual stress have a significant influence on fatigue life of welded joints. In order to reduce the stress concentration of welded joints, a mathematical design method of tensile triangles (MTT) based on bionics was applied to weld shape design. Accordingly, the stress concentration of various weld beads in the corner boxing welded joint and the fillet welded T-joint was dissected using our in-house FEM software JWRIAN. It was found that there existed a large stress concentration in the conventional welded joints, whereas those welded joints with elongated weld bead were accompanied by a lower stress concentration, especially for elongated weld bead with MTT design. Furthermore, among the weld shapes of the corner boxing fillet welded joint, the rectangle shape of weld bead had the minimum stress concentration factor (1.05). For the fillet welded T-joint with MTT design, the stress concentration of weld toe decreased dramatically with the increase of the index of designed shape, but there was a minor difference of stress concentration at weld root between the weld beads with MTT design. In addition, application of low transformation temperature (LTT) weld metal utilizing martensitic transformation to the fillet welded T-joints can produce compressive residual stress at weld toe.

Simulation and analysis of electron beam welding residual stress in thin-walled high-temperature alloy aeroengine structures

Electron beam welding (EBW) is widely used to connect thin-walled high-temperature alloy structures in aeroengines. However, the residual stress and deformation caused by the high-temperature gradients generated during welding would affect the rigidity, dimensional stability, and fatigue resistance of the welded structures. The study reported here used a model combining ellipsoidal and Gaussian rotating body heat sources to undertake a numerical simulation of the temperature and residual stress generated during the EBW process. The model was systematically refined by observing and measuring the molten pool morphology. The error rates for key dimensions determining the molten pool shape were less than 6%. With a microscope-based examination, the energy distribution characteristics were detected by the microstructure analysis of grain type and size in different regions to verify the viability of the heat source model. The residual stress of a butt welding was simulated by the proposed heat source model based on the full consideration of a full-loop thin-walled combustor casing structure and material properties. It was found that the average errors for longitudinal and transverse residual stresses of welded joints and their adjacent areas were 10% and 12%, respectively, by comparing with the experimental results. Simultaneously, the low cycle fatigue life of the welded combustor casing would be decreased by 32% considering the influence of welding residual stress. These conclusions can be used as a basis for studying the integrity of thin-walled welded structures in aeroengines.

Анализ влияния вида сварки на фазовый состав и внутренние напряжения сварных соединений аустенитных и дуплексных сталей

A literature review and own investigations of the impact of a welding kind and post-welding thermal treatment upon a phase structure and residual stresses of welded joints are carried out. It is defined that such high-performance and promising welding kinds as electronic-beam welding (EBW) and laser welding (LW) have a negative impact upon a phase structure of two-phase (duplex) and single-phase steels as a result of high cooling rates of welded joints.