Stresses In Welded Joints Research Articles

Numerical investigation of residual thermal stresses in welded joints of heterogeneous steels with account of technological features of multi-pass welding

The paper describes a two-dimensional mathematical model to evaluate stresses in welded joints formed in multi-pass welding of multi-layered steels. The model is based on a system of equations that includes the Lagrange's variational equation of the incremental theory of plasticity and the Biot's variational principle for heat transfer simulation. In the constitutive equations, the changes in the volume which occur as a result of phase transitions can be taken into account. Therefore, the prehistory and impact of thermal processing of materials on macroscopic properties of the medium can be considered.The variational-difference method is used to solve both the heat transfer equation for calculation of the non stationary temperature field and the quasi-static problem of thermoplasticity at each time-step. The two-dimensional problems were solved to estimate the residual thermal stresses (for the case of plane stress or plane strain) during cooling of welds and assessing their impact on strain localization in the heat-affected zone under tensile and compressive loading considering differences in mechanical properties of welded materials.It is shown that at initial stages of the plastic flow, the residual stresses significantly affect the processes of stress concentration and localization of strains in welded joints. To estimate the model parameters and to verify the modeling results, the available experimental data from scientific literature obtained on the basis of the Satoh test for different welding alloys was used.

Investigation of residual stresses in welded joints of heat-resistant magnesium alloy ML10 after electrodynamic treatment

Abstract In repair of aircraft structures of magnesium alloy ML10, the argon arc non-consumable electrode welding is used. In this case, the residual welding stresses occur in repair welds, being one of the causes for reducing the service characteristics of the restored products. Residual stresses arise as a result of welding. Post-weld heat treatment is used to reduce the residual stresses. The heat treatment, which occurs after welding, increases the cost of repair. This leads to the search for alternative methods to control the stressed state of welded joints, one of which is electrodynamic treatment, which reduces the level of residual stresses in repair welds, and as a consequence, the cost of the welding repair in restoring aircraft structures. It was found from the results of experiments carried out, that the electrodynamic treatment allows reduces the initial level of stresses in welded joints, reaching 120 MPa, to 30 MPa, and at definite geometric characteristics of the specimens forming the field of compressive stresses, the values of which are equal to –50 MPa. It is shown that the optimum distance between the zones of treatment, being 5 mm, provides the guaranteed covering the zones of electrodynamic effect and, as a consequence, the maximum efficiency of the electric dynamic treatment.

A method of determining structural stress for fatigue strength evaluation of welded joints based on notch stress strength theory

This paper presents a new method to evaluate the structural stress in welded joints. The method is based on notch stress strength theory, 1mm stress method and the ‘equivalent zero point’ stress method. According to notch stress strength theory, a simple method with the singularity strength ‘as’ is used to estimate the stress field distribution at the corner. Moreover, a modified methodology for fatigue strength assessment, has been developed, starting from a cruciform model, and then further developed to realistic ship structural components. Validity of this method is further verified by analyzing the stress results for several typical welded joints reported in literature. The results show that the proposed method has the additional advantage in simplified fatigue strength estimation for welded joints and it is able to account for the thickness effect observed in welded joints.

RESEARCH OF VERTICAL FILTER’S BODY’S WELDED JOINTS CRACK’S AND DEFECT’S CAUSES

Results of research of vertical filter’s welded joints crack’s and defect’s causes at the stage of manufacture are shown in this paper. One of the main causes of the shape’s deformation and cold cracks are significant internal stress in welded joints. In accordance with this changes in ovality of welded body at different stages of manufacture was analyzed. The experiments were carried out at the real existing production’s structures in the field. For housings vessels and equipment, which work under pressure one of the criteria of manufacturing quality is accordance of the geometric parameters to requirements of federal regulations. Among the main controlled parameters in accordance with GOST R 52630-2006 is a relative roundness of the apparatus. In these regulatory documents maximum level of internal stresses is not regulated. Thus, manufacturers try to reduce all means relative roundness, often creating a critical design loads that result in the formation of cold cracks on the design stage of manufacture, or in first months of operation. One of the manufacturing operation affecting the roundness of the housing unit is the process of welding the fitting to the sidewall, while the larger diameter welded fitting, the greater the deviation. In this paper, the technology of manufacturing the filter housing is welded to the two opposing tube, the total diameter greater than the diameter of the filter housing. The paper provides an analysis of the existing manufacturing technology used in the production, said method is used to reduce welding deformation. The absence of mandatory requirements for reducing internal stresses in such structures leads to the creation of constructions with high level of internal stresses, that fact significantly increases the probability of cold cracking. The appearance of the stress-strain state induced by this operation is described in many research projects. However, this fact is not taken in the account in real manufacture. Results shown in this paper demonstrates the influence of welding processes for possible deviations of the geometric shape of the hull unit and allows to provide at the stage of process development compensatory measures.

An extrapolation method to determine the effective notch stress in welded joints

AbstractThis paper presents the development of an extrapolation method to estimate the notch stress in welded steel joints, in line with the effective notch stress concept described in the International Institute of Welding guideline. The proposed approach provides a convenient method to determine the local notch stress at the weld toes without the need to model a finite notch radius as required in engineering guidelines, which creates significant modeling challenges in the numerical procedure, especially for 3‐D joints with a complex topology. An experimental study validates the feasibility of this extrapolation method through strain measurements on cruciform joints. The numerical study then investigates two types of welded connections: (1) cruciform joints with full‐penetration welds and (2) tube‐to‐plate joints. The proposed extrapolation method provides accurate effective notch stress estimations on both joint types, compared with the effective notch stress calculated following the mesh requirement in the existing guidelines.

Impact of Electrode Wire Feed Ways on Residual Stresses in Welded Joints

A series of experiments have been done to evaluate the way an electrode wire feed affects residual stresses in welded joints. It was found that an electrode wire pulse feed combined with shielding gases decreases residual stresses up to two times in comparison with welding with a continuous feed of an electrode wire.

Characteristics of the stress–strain state of annular welded joints in pipelines made of low-carbon austenitic steel

The welding technology using Russian welding materials is described and the nature of formation of residual welding stresses in annular welded joints in pipelines of 3161 low-carbon austenitic steel is outlined. The distribution of stresses in the welded joint at elevated temperatures is simulated.

Evaluation of Residual Stresses in Carbon Steel Weld Joints by Ultrasonic L $$_\mathrm{{cr}}$$ cr Wave Technique

Ultrasonic based residual stress measurements are nondestructive and offer quantitative estimation of surface/sub-surface and bulk residual stresses. The underlying principle of the ultrasonic techniques is the ‘acoustoelasticity’ i.e. the stress dependence of ultrasonic velocity. Three pairs of 20 mm thick low carbon steel weld joints were fabricated using manual metal arc welding process with three marginally different heat inputs (optimum, marginally below optimum and above optimum) and used in the study. Critically refracted longitudinal (L $$_\mathrm{{cr}}$$ ) ultrasonic wave technique was employed for this study. This paper gives the details of development of ultrasonic L $$_\mathrm{{cr}}$$ wave based technique for residual stress measurements and the quantitative estimation of surface/sub-surface residual stresses in carbon steel weld joints. The study indicates lower value of tensile residual stress in weld joints made using marginally below optimum heat input when compared to the residual stress values in weld joints made using optimum and marginally above optimum heat inputs. The developed ultrasonic L $$_\mathrm{{cr}}$$ wave technique is found to be very sensitive even to the small variations in the residual stress profiles across the weld joints induced by marginally different heat inputs employed during welding.

Study of Residual Stresses in Welded Joints of Heat-Resistant ML10 Magnesium Alloy After Electrodynamic Treatment

Airframes from ML10 magnesium alloy are repaired using argon-arc welding with nonconsumable electrodes. The residual stresses occurring in the repair welds deteriorate the operating characteristics of restored parts. The presence of residual stresses necessitates postweld heat treatment, which increases the prime cost of repair operations. This implies the option of applying the alternative methods of weld stress state adjustment, including the electrodynamic treatment, which make it possible to reduce the level of residual stresses in welded joints and, thus, the cost of repair welding operations for airframes from this alloy. The results of the performed experiments show that electrodynamic treatment allows one to reduce the initial level of stresses in welded joints (which reaches 120 MPa) to 30 MPa and to form, at definite geometric characteristics of specimens, compression stress fields in the treatment zone, whose values reach –50 MPa. It is demonstrated that the optimal distance between the treatment zones is 5 mm, which ensures granted overlapping of electrodynamic action zones and, hence, the maximum effectiveness of electrodynamic treatment.

On Welding Residual Stresses Near Fatigue Crack Tips

Residual stresses in welded joints are supposed to change during fatigue loading. Residual stresses can be, depending on the loading conditions, relaxed as well as build up and they can be affected by fatigue crack growth. Furthermore residual stresses are supposed to affect the fatigue strength of welded steel structures. However, tensile residual stresses decrease and compressive residual stresses increase the fatigue strength. This residual stress effect on the fatigue strength is mostly explained with different crack propagation rates.The presented work is on welded longitudinal stiffeners, made of unalloyed fine grained carbon steel, with different fatigue crack lengths in which residual stresses have been determined. The residual stress measurement was conducted using Neutron diffraction. The results of the diffraction measurement show that the initial tensile residual stresses near the weld toe are, caused by phase transformation at low temperatures, below the base materials yield strength. Tensile residual stresses in the order of the yield strength can be found below the materials surface. These areas of high residual stresses are moving with the propagating crack tip through the specimen during fatigue loading.

Distribution of residual stresses in welded joints in 09G2S steel produced by adaptive pulsed-arc welding

Results of investigations into the effect of conditions of adaptive pulsed-arc welding on the mechanical properties and distribution of residual stresses in welded joints in plates of 09G2S low-alloy steel are presented. Pulsed-arc welding increases the impact toughness of the weld metal at subzero temperatures in comparison with the stationary conditions, and compressive residual welding stresses were detected.

Application of low Ms temperature consumable to dissimilar welded joint

The welding of dissimilar joints is very common in systems used in oil exploration and production in deep sea waters. Commonly involves welding of low carbon steel pipes with low alloy steel forgings both with inner Inconel clad. The forged steel part undergoes a process of buttering with Inconel or carbon steel electrode before the weld of the joint. The buttering process is followed by a process of residual stresses relief. The conventional way of reducing the level of residual stresses in welded joints is to apply post welding heat treatments. Depending on the size and complexity of the parts to be joined, this can become a serious problem. An alternative technique for reducing residual stresses is to use an electrode that during the cooling process undergoes a displacive transformation at a relatively low temperature so that the deformation resulting from the transformation compensates the contraction during the cooling process, and, although many papers have been published in this direction using Fe–Cr–Ni alloys, most of them report a loss of toughness in the weld metal. Maraging steel is a family of materials with Ms temperature below 200°C and even without the final heat treatment of aging has superior mechanical properties to low alloy steels used in forgings. In this work, forged piece of AISI 4130 was buttered with Maraging 350 weld consumable and subsequently welded to ASTM A36 steel using Inconel 625 filler metal. In addition, the dissimilar base metal plates were welded together using Maraging 350 steel weld consumable. The levels of residual stress, and the toughness and microstructures of heat affected zone and weld metal were investigated.

An Assessment of the Mechanisms of Transformation Plasticity in SA508 Grade 3 Steel during Simulated Welding Thermal Cycles

Residual stresses in welded joints must be quantified in order to carry out structural integrity assessments on critical nuclear components. This usually requires the application of finite element models for components with wall thicknesses exceeding 50 mm. In ferritic steels, the development of residual stresses is made more complex by the strains associated with the solid-state phase transformations that occur during heating and cooling. Finite element models often do not account for factors that contribute to anisotropy in the transformation strains, such as Greenwood-Johnson plasticity and variant selection. In this work, we search for evidence that might reveal which mechanism (s) contributes to this anisotropy. Coupons of SA508 steel were subjected to simulated welding thermal cycles, with and without external loading, and in-situ X-ray diffraction was used to track changes in crystal structure. The results were checked for evidence of plastic deformation in austenite and variant selection in its daughter phases.

The use of conventional strain gauges evaluation for measurements of residual stresses in welded joints

Residual stresses (RS) can reach significant values in a welded joint, committing the quality of the parts since they affect their resistance to fatigue causing cracks and corrosion under stress. The use of strain gauges positioned in specific zones of welded parts, as a way of mapping the RS values from the welding processes, has a great technological interest. The method proposed in this paper defines strategic positions for strain gauges along ASTM A36 steel plates in butt-welded joints using Gas Tungsten Arc Welding. Helped by a signal conditioner, RS values were collected and registered after welding process. The results are the readings of RS imposed by the welding operation, taking into account thermal process effects and the material properties. Experimental results were compared with numerical analysis, via Finite Element Method which showed the potential use of strain gauges for measuring RS from the welding process.

Increasing the reliability of welded joints in high-strength V-1461 aluminium–lithium alloy

Filler materials for welding V-1461 alloy, ensuring high cracking resistance, corrosion resistance and mechanical properties, are selected. The results of tests of the welded joints in static tensile loading and bending and the impact toughness of the weld metal and low-cycle fatigue strength are presented. The experimental results show that the application of impact ultrasound treatment increases by an order of magnitude the values of low-cycle fatigue resistance of the welded joints as a result of the formation of the nanostructured surface layers. The level of residual stresses in welded joints is determined.

The Effect of UIT on the Residual Stress of 7N01 Al-Alloy Welding Joints

The X-ray diffraction method (iXRD) has been applied into the measurement of residual stress ultrasonic impact ultrasound before and after the impact test process residual stress of aluminum alloy welded joints. Research different inrush current, different impact time of different ultrasonic impact of the process on the residual stress of welded joints of aluminum alloy welded joints welding residual stress distribution and its variation. We can study the distributing status and disciplinarian, and testify the step to adjust the welding residual stress by ultrasonic impact treatment. The research supplys the data supports for welding residual stress engineering disposal and weld joint assistant consolidation to improve abilities against the gatigue. The research shows appropriate welding and ultrasonic impact treatment technics can effectively adjust welding residual stress and meet the RAMS demands about the product.

Assessment of Residual Stresses and Distortion in Stainless Steel Weld Joints

Welding introduces significant residual stresses in the welded structure/component due to non-uniform heat distribution during heating and cooling cycle. To control, reduce, or beneficially redistribute the residual stresses in weld joints, the stress distribution needs to be known. In the present study, weld joints of 10 mm thick 316LN stainless steel were made by multi-pass TIG and A-TIG welding processes and their residual stresses distribution and distortion values were measured and compared. While V-groove edge preparation was required for making multi-pass TIG weld joint, square-edge preparation was sufficient for making single pass A-TIG weld joint. Ultrasonic nondestructive technique based on the critically refracted longitudinal waves (LCR waves) has been used for the quantitative surface/sub-surface residual stress measurements in the weld joints. Distortion measurements were carried out before and after welding using height gauge. Peak tensile residual stress and the angular distortion values were lower in the A-TIG weld joint compared to that of the multipass TIG weld joint.

Redistribution of residual welding stresses in ultrasound impact treatment of welded joints in pipes

Results are presented of the investigation of the distribution of the residual welding stresses in welded joints in pipes with a diameter of 720 mm, wall thickness of 8 mm, produced from 13G1SU steel, after welding operations and the effect of ultrasound impact treatment on the redistribution of stresses is investigated.

Measurement and Simulation of Residual Stresses of Electron Beam Welding Joint of Pure Aluminum

The effects of electron beam welding on the residual stresses of welded joints of pure aluminum plate 99.60 are studied by through-hole-drilling and blind-hole-drilling method. Meanwhile, based on the thermal elastic-plastic theory, and making use of ANSYS finite element procedure, a three - dimensional finite element model using mobile heat source of temperature and stresses field of electron beam welding in pure aluminum is established. The welding process is simulated by means of the ANSYS software. The results show that the main residual stress is the longitudinal residual stress, the value of the longitudinal residual stress is much larger than the transverse residual stress. But the residual stress in the thickness is rather small. And in the weld center, the maximum value of residual stresses is lower than its yield strength. The simulation results about the welded residual stresses are almost identical with the experimental results by measuring. So the research result is important to science research and engineering application.

Determination of the triaxial distribution of residual stresses in welded joints of structural elements with rectilinear seams and estimation of their influence on joint strength in the presence of crack-type defects

On the basis of a three-dimensional theory, we consider a mathematical model of a welded joint of plane structural elements with rectilinear seams. These joints are simulated by a plane layer with rectilinear seam with residual stresses. Using the method of direct integration of key equations without additional potential functions, we obtain expressions for components of the stress tensor for a set of given inconsistent residual strains localized in the weld. We investigate the influence of residual stresses on the static strength of this welded joint with sharp defects simulated by external surface cracks. Using a two-parameter criterion for brittle-ductile fracture, we calculate the load factors for a welded joint with a crack in the weld.