Stress Distributions In Welds Research Articles

Interfacial characteristics and residual welding stress distribution of K4750 and Hastelloy X dissimilar superalloys joints

Gas tungsten arc welding (GTAW) method was employed to join a newly developed cast superalloy K4750 with Hastelloy X by using K4750 and Hastelloy X filler metals (FMs), respectively. Thereby we obtained two kinds of interfaces namely K4750 base metal (BM) and Hastelloy X FM, and K4750 FM and Hastelloy X BM. The elemental distribution, interfacial characteristics, and the residual welding stress of the dissimilar joints were investigated by electron probe micro analyzer (EPMA), electron backscattered diffraction (EBSD), and section technique, respectively. The results showed that the elemental distribution across both interfaces were varied significantly. And the composition segregation regions were identified in both interfaces but the segregation extent was different. Epitaxial growth was clearly observed in both interfaces. The distribution of the residual welding stress across the joint exhibited that the highest tension stress area in both as-welded joints was located at the joint heat affected zone (HAZ). The residual welding stress in the joint with Hastelloy X FM was significantly relieved through post weld heat treatment (PWHT).

The effect of elastic modulus of adhesive on stress-distribution in weld bonded joint of Al 6082-T6 sheets

Abstract The single lap joints were obtained with sheet metals of Al 6082-T651 alloy of thickness 2 mm and epoxy of two components. The strength of weld-bonded joints is found significantly higher than equivalent resistance spot welded joints. The role of elastic modulus of adhesive has been investigated computationally to find its affect on the pattern of stress distribution in the overlapped region. Prior to FE analysis experiments have been performed to find the weld characteristics to be utilized in the development of FE model.

Experimental Investigations on Welding Stress Distribution in Thick Specimens After Postweld Heat Treatment and Ultrasonic Impact Treatment

This paper presents the welding residual stress distribution in thick specimens after postweld treatments (postweld heat treatment—PWHT, and ultrasonic impact treatment—UIT). Three specimens with a thickness of 40 mm were multipass butt-welded by the gas metal arc welding (GMAW). The surface stresses were evaluated by the hole-drilling (HD) and the x-ray diffraction (XRD) methods, while the internal stresses were determined by the contour method (CM). It is found that UIT has a local effect on the welding residual stress. It can convert the tensile welding stresses into compressive stresses and introduce about a 3-6 mm compressive stress layer at the treated surface with little effect on the stresses outside the treated region and the stress distribution in the interior weld zone. Additionally, UIT shows the same effect on the surface longitudinal and transverse stresses, which results in a similar distribution and magnitude of compressive longitudinal and transverse stresses on the treated regions. PWHT has a global stress release of the welding residual stress, resulting in almost uniform stress distribution in the specimen with the range from − 200 to 100 MPa. PWHT also causes the release of the compressive transverse stress in the interior.

Welding-induced buckling prediction for large thin-walled cylindrical structures with non-uniform stress fields by friction stir welding

The non-uniform welding stress distribution in large thin-walled cylindrical structures easily causes the buckling distortion due to weak structural stiffness and nonlinear geometric deformation. The non-uniform temperature field model induced by friction stir welding is analytically developed and is used to theoretically deduce the non-uniform stress model in the weld region. Both the two models are verified by the experimental data. A prediction model of critical buckling load is established for large thin-walled cylindrical structures considering the non-uniform welding stress distribution. The deflection function for buckling analysis is developed by using polynomials and the Chebyshev polynomials of the first kind that satisfy the boundary conditions along the four edges of the structure. The critical buckling loads are calculated for various cylindrical welded shell structures, which obviously decrease with the increase of the diameter-thickness ratio and the length-diameter ratio. The mitigation of buckling distortion is achieved by the correlation of the buckling load and the welding stress with various welding process parameters. The results are beneficial for the determination of geometric configuration and welding process parameters for large thin-walled cylindrical structures in fabrication of propellant tanks of launch vehicles.

Method of X-ray residual stress measurement for phase transformed welds

In this study, we attempted to evaluate the residual stress distribution in welds accompanied by phase transformation using X-ray stress measurement. First, relationship between the phase transformation behavior and the residual stress of welded specimens with different phase transformation was discussed. In the specimen with martensite in the weld, reduction in tensile stress due to martensite transformation shown in residual stress distribution followed conventional behavior. However, in the specimen with bainitic ferrite in the weld, the residual stress in the transverse direction was almost the same as the residual stress in the longitudinal direction, and the residual stress did not follow conventional behavior. Next, X-ray elastic constant in the weld was measured, and then the residual stress was reevaluated. In the specimen with bainitic ferrite in the weld, X-ray elastic constant had anisotropy, and the reevaluated residual stress followed conventional behavior. In conclusion, it was shown that depending on the phase transformation behavior, it is difficult to use X-ray elastic constant estimated by Kröner model; however, if we use the measured value, we are able to evaluate the residual stress more accurately.

Analysis of Retained Austenite and Residual Stress Distribution in Ni-Cr Type High Strength Steel Weld by Neutron Diffraction

Prevention of weld cracking is necessary for ensuring the reliability of high strength steel structures. Tensile residual stress in the weld metal is one of the major factors causing the weld cracking, therefore, it is important to clarify the residual stress distribution in the weld metal. Conventional stress measurement, the stress relief method using strain gauges and the X-ray diffraction technique, can only provide the stress information in the surface region of the steel weld. The neutron diffraction is the only non-destructive method that can measure the residual stress distribution inside the steel weld [1-3]. The neutron stress measurement was applied for the 980MPa class high strength steel weld and it was revealed that high level of tensile residual stress can affect the weld cracking to a significant degree [4-5]. Recently, it was reported that Ni-Cr type steel weld exhibit higher resistance to the weld cracking compared with conventional low alloy type weld. Increase of tensile residual stress is prevented by lower transformation temperature of the Ni-Cr type weld metal and retained austenite phase is dispersed in the martensite microstructure. It is considered that lower level of tensile residual stress and the existence of retained austenite may prevent hydrogen accumulation in the weld metal [6]. However, retained austenite and the residual stress conditions in the Ni-Cr type high strength steel weld is not well understood. In this study, neutron diffraction analysis was conducted on the Ni-Cr type steel weld joint with the tensile strength level of 980MPa in order to investigate the effect of the retained austenite and the residual stress distribution on the weld cracking.

Welding stress relaxation effect in butt-jointed steel plates

This paper presents an experimental study of the behavior of the residual welding stresses for butt-jointed steel plates. Two different welding processes were used to joint the plates, one with a single electrode and the other with double electrodes. The stresses were monitored over two weeks after the removal of the welding constraints. The measurements were performed at the deposited metal, the heat-affected zone, the base metal close to the weld joint and along the plate using the X-ray diffraction method and magnetic method based on the magnetostriction effect. The experimental results showed the continuous process of welding stress relaxation over a relatively short length of time with a significant difference in the final welding stress distribution from just after the removal of the welding restraints, both for the single-electrode and the double-electrode welding. The observed stress redistribution trend was characterized by a reduction in and a uniformity of the values of the maximum shear stresses. Microstructure analysis showed the absence of microcracks at the deposited metal, the heat-affected zone and the base metal close to the weld joint at the welded specimens. Thus, the possibility that the observed welding stress relaxation was the result of material failure is ruled out.

The Effect of Plate-Plate Butt Welding Stress Distribution on the Welding Deformation

In this paper, the distribution of residual stress is measured which is 60mm away from the weld center with the three-dimensional magnetic measurement apparatus of HZ-21. The stress distribution of plate - plate butt welding and its influence on welding deformation are studied. The results show that, plate - plate butt of Q235B steels, the welding stress distribution of σx direction is in the direction of a curve along the seam; 24 hours after welding, the welding angular deformation increases due to the changes of welding stress, while welding angular deformation also changes the stress distribution.

Numerical and experiment analysis of residual stress on magnesium alloy and steel butt joint by hybrid laser-TIG welding

Hybrid welding technology has received significant attention in the welding of dissimilar materials recently. While, great welding residual stress and deformation often result by the difference of coefficient of thermal expansion This study describes the thermal elastic–plastic analysis using finite element techniques to analyze the thermo mechanical behavior and evaluate the residual stresses and welding distortion on the AZ31B magnesium alloy and 304L steel butt joint in laser-TIG hybrid welding. A new coupled heat source model was developed which combined by double-elliptic planar distribution, double-ellipsoid body distribution and Rotary–Gauss body distribution model. From the results, it can be concluded that the temperature distribution at the hybrid weld region is exposed to faster rate of heating and cooling in hybrid welding than TIG. Furthermore, compared to the welding stress distribution on the TIG weld, residual stress σy is found about 20% higher on hybrid weld joints, and the residual stress on the 304L steel plate is lower than that on the AZ31B magnesium plate.

980MPa級高張力鋼抵抗スポット溶接部におけるナゲット寸法および残留応力の数値シミュレーション

High-strength steel sheets of HT980-class are beginning to be used for automobile bodies in order to reduce body-weight and improve fuel-efficiency. Resistance spot welding is an important method in joining of high-strength steel sheets. The microstructure of welds becomes martenstic structure and high tensile residual stress is generated. It is important to ensure the performance of resistance spot welds in order to use high-strength steels more widely in automobiles. Therefore, the evaluation of characteristics of resistance spot welds is quite important.In this study, residual stress of resistance spot welds of HT980 sheets were investigated by numerical simulation and X-ray stress measurement. First, resistance spot welded test pieces were fabricated and nugget formation process was observed. Residual stress distribution in the welds of the test pieces was measured by X-ray diffraction method with a two-dimensional detector. High tensile residual stress was measured in the spot welds. The measurement results for the three test pieces were comparable. Second, residual stress distribution in the resistance spot welds was calculated by current-temperature-microstructure-mechanics coupled simulation. Comparison between the experiment and the numerical simulation proved that nugget formation process was reproduced by the simulation. Residual stress distribution obtained by the simulation was in good accordance with the measurement results when initial residual stress in HT980 sheet before welding was taken into consideration.

A computational procedure for evaluating the J-integral for mode І crack in welds: A 3-D finite element analysis

Abstract In this study, a computational procedure capable of evaluating the J-integral for mode I crack in welds is presented. An uncoupled three-dimensional thermal elastic–plastic finite element method is utilized to obtain residual stress distributions in welds. The resulting residual stress fields are then fed into the subsequent fracture mechanics analysis of mode I crack in welds. Moreover, analytical expression of the J-integral for mode I crack in a three-dimensional residual stress bearing body which yields domain-independent values is given in a form suitable for the numerical analysis. The J-values for the combined residual and mechanical loading are calculated and discussed.

Effect of Weld Parameters on Residual Stress Distribution in Flux Cored Arc Welding of High Strength Low Alloy Steel

Various types of high strength steels are increasingly used for producing welded structures with reduced weight and improved performance. Welding problems related to residual stress and distortion can arise, since yield stress of these steels are high, there is always a possibility of producing very high residual stresses in some locations near the weld. In general residual stresses become dangerous if they lead to local multi axiallity of tension stresses, which favour brittle fracture, knowledge of the residual- stress distribution in welds is necessary in order to assess the risk of crack growth in service The distribution of residual stresses after welding depends strongly on the weld parameters Attempts were made to study the influence of weld parameters (arc voltage, travel speed, welding current) on residual stresses pattern of high strength low alloy steel weldments This study was mainly performed by using X-ray stress analyzer.

Residual stress in laser welded dissimilar steel tube-to-tube joints

Austenitic-ferritic dissimilar steel joints are widely used in power generation systems. Their utilization has proved to be efficient in terms of satisfactory properties and the economics. These types of joints have usually been produced using conventional welding processes, such as tungsten inert gas (TIG) welding. With the rapid development of high power lasers, laser welding has received considerable attention. Laser welding offers many advantages over conventional welding processes, e.g. low heat input, small heat-affected zone (HAZ), small distortion, and welding in an exact and reproducible manner. Residual stress distribution in laser welds may also differ from those made by conventional welding processes due to its special features. Residual stress, particularly tensile residual stress in the weld, can be very important factor in controlling the quality and service life of the welded structure. The formation of tensile residual stress in the weld may result in the initiation of fatigue cracking, stress corrosion cracking or other types of fractures. It is useful, therefore, to understand the distribution of residual stress in austenitic-ferritic laser welds, and thus evaluate the quality of the joints. Although residual stress distribution in the welded joints has been extensively investigated, little data are available for the residual stressmore » distribution in laser welds. The aim of the work was to examine residual stress distribution along laser welds of dissimilar steel tube-to-tube joints, which were made by both autogeneous welding and welding with filler wire. The results were also compared with the joints made by plasma arc and TIG welding.« less

Strengthening of wide-flange columns under load

The present work deals with formulation of theoretical and analytical methods leading to the development of column strength curves. The formulations were developed for both elastic and inelastic behaviour. Two types of reinforcement have been developed for strengthening the W-shape columns under load. Since the column strength curves are based in part on the magnitude and distribution of residual stresses, it is extremely important to consider the new pattern of residual stresses due to welding process. Also, the welding sequence will affect the magnitude and distribution of residual stresses. Theoretical formulations leading to a closed-form solution for the prediction of critical load were developed for two types of strengthening using the superposition of original residual, new welding, and initial loading stresses. A nonlinear finite element analysis based on the large deformation theory of stability was used to predict the strengthened column critical load. It takes into consideration the effect of cooling residual stresses and new welding residual stresses. The formulations were incorporated with gradual penetration of yielding, the spreading of inelastic zones along the member length, the presence of residual stresses, and strain hardening of the material. Experiments were carried out to determine the actual capacity of strengthened columns. Seven specimens were tested using two and four strengthening plates. The welding stresses were measured through a series of experiments, and it was found that the parabolic distribution is a very close approximation to the actual new welding stress distribution. Key words: reinforcement of steel columns, welding stresses, welding sequence, strengthening of existing structures, buckling, steel plating, finite element.

光干渉を利用した溶接部の残留応力分布 Ｉ 観察原理とその適用例

This paper describes a new measuring method of residual stress distributions in welds qualitatively using an optical interference method. The principle of this method is based on measuring by an interference fringe (surface relief), induced on a specimen when deformed and/or treated by stress-relief annealing. The method may be characterized mainly in the following measurements:1) Only by lapping a surface of a specimen, the location of stress concentration and the range of plastic deformation can be easily known.2) Combined with cutting and annealing, unique patterns of surface relief are revealed respectively due to stress release in z-, xy-, and xyz- directions.3) This method can be also utilized under subzero temperature, and furthermore, even at higher temperature by use of a laser.

光干渉を利用した溶接部の残留応力分布 ＩＩ 溶接残留応力と溶接割れ

In previous report, a new method was introduced for obtaining residual stress distributions in welds qualitatively by measuring surface relief induced due to cutting and annealing.This paper presents the micro-distributions of residual stress in welds obtained by this new method in four kinds of steel having a different transformation characteristics.Based on these test results, some considerations are performed on the micro-mechanism of welding residual stress, and it is clarified that a cause of reheat cracking by a subsequent welding pass occured in multi-pass weld of high strength steels.