Study on residual stress in socket weld by numerical simulation and experiment

Tensile residual stresses at the surface of welded components are known to compromise fatigue resistance through the accelerated initiation of microcracks, especially at the weld toe. Inducement of compression in these regions is a common technique employed to enhance fatigue performance. Transformation plasticity has been established as a viable method to generate such compressive residual stresses in steel welds and exploits the phase transformation in welding filler alloys, that transform at low temperature to compensate for accumulated thermal contraction strains. Neutron and X-ray diffraction have been used to determine the stress profiles that exist across the surface of plates welded with low transformation temperature welding alloys, with a particular focus on the stress at the weld toe. For the first time, near-surface neutron diffraction data have shown the extent of local stress variation at the critical, fusion boundary location. Compression was evident for the three measurement orientations at the fusion boundaries. Compressive longitudinal residual stresses and tensile trans- verse stresses were measured in the weld metal.

Residual stresses that arise as a result of welding can cause distortion, and also have significant implications for structural integrity. Martensitic filler metals with low transformation temperatures can efficiently reduce the residual stresses generated during welding, because the strains associated with the transformation compensate for thermal contraction strains during cooling. However, it is vital that a low weld transformation temperature is not obtained at the expense of other important material properties. This article outlines the alloy design process used to develop appropriate low transformation temperature filler materials for the mitigation of residual stresses in both low alloy ferritic and austenitic stainless steel welds. Residual stresses in single pass, 6 mm bead in groove welds, on 12 mm thick plates, have been measured and compared against those obtained with commercially available conventional austenitic and ferritic filler materials. The filler metals developed here exceeded requirements in terms of weld mechanical properties, while significantly reducing the maximum residual stress in the weld and heat affected zone.

To investigate the distribution pattern and magnitude of residual stress at the weld toe of pipe-sphere connections in welded hollow sphere joints, the blind-hole method was employed to measure welding residual stress at both the spherical weld toe and pipe weld toe, yielding the magnitude and distribution characteristics of the residual stress. Additionally, the VISUAL-Environment finite element simulation software was utilized to obtain the temperature field, residual stress field, and residual stress distribution curves at the weld seam. The results indicate that welding residual stress in the entire welded hollow sphere joint exhibits both periodic and stochastic characteristics, with these two patterns showing good consistency. Meanwhile, finite element analysis results reveal the presence of both residual tensile and compressive stresses on the spherical surface and the connected pipe, with the welding residual stress maintaining a self-equilibrated state across the entire specimen. This study provides a foundational basis for subsequent research on the fatigue performance of grid structures with welded hollow sphere joints.

Residual weld stresses in stiffener-to-deck plate weld of an orthotropic steel deck

Tensile residual stress is a major issue in integrity of the welded structures. Undesirable tensile residual stress in welding may reduce fracture toughness and fatigue life of welded structures. The low transformation-temperature (LTT) fillers, due to introducing compressive residual stresses caused by prior martensitic transformation, can reduce tensile residual stresses in the weld zone. The effects of using LTT fillers on welding residual stresses of high strength steel sheets are studied and compared with conventional fillers. 3D finite element simulations including coupled thermal-metallurgical-mechanical analyses are developed using SYSWELD software to predict the welding residual stresses. For validation of the finite element model, the residual stresses are measured through hole drilling strain gage method. The results indicate that using the LTT fillers cause a decrease of the longitudinal tensile residual stresses of the weld metal from 554 MPa to 216 MPa in comparison with conventional fillers. The transverse residual stresses of the weld line are changed from tensile 156 MPa to compressive 289 MPa with using LTT fillers instead of conventional fillers.

ABSTRACTTo understand the cause of compressive residual stress in welded joints, we analysed by numerical analysis the effect of welding pass sequence using low transformation temperature (LTT) welding materials on residual stress around the weld toe of boxing fillet welded joints. It was determined by numerical analysis that the produced compressive residual stress and the influence of the stiffeners are reduced in the equivalent position of the weld toe in a fillet welded joint because of the influence on the behaviour of the stiffener in the weld being due to residual stress distribution around the weld toe. The residual stress reduction method of extending the length of the welded bead and releasing the weld toe from the stiffener, similar to the concept of discarding a bead to reduce tensile residual stress, was effective in fillet welded joints. Numerical analysis of the relationship between residual stress around the weld toe and width of the weld bead in the bead-on-plate welding model clarified that compressive residual stress can be introduced around the weld toe by having a wide width weld bead. In addition, a fully penetrated welded joint was very effective for causing compressive residual stress around the weld toe.

Welded steel plates are widely used in various structural applications, and the presence of inclined welds is often encountered in practical scenarios. Carbon fiber reinforced polymer (CFRP) has been proven to be effective for strengthening steel structures. However, the behavior of CFRP-strengthened welded steel plates with inclined welds, particularly considering the influence of welding residual stress, is limited. This paper aims to investigate the tensile behavior of CFRP-strengthened welded Q355 steel plates with inclined welds considering welding residual stress (WRS). First, WRS data were obtained by the X-ray diffraction (XRD) method at different locations. The maximum tensile and compressive residual stresses are 0.39 and 0.14 times the yield strength of the steel, respectively. Then, finite element models were established to investigate the effects of weld angles, weld width, and height on the WRS distribution of welded steel plates. Finally, the tensile performance of CFRP-strengthened welded plates with WRS was studied by numerical simulation. The results showed that the weld angles have little effect on the distribution pattern of residual stress but significantly affect the peak tensile WRS. When the weld angle changes from 0° to 60°, the peak tensile WRS decreases significantly from 0.32 to 0.06 times the yield strength of steel; furthermore, the influence of weld width and height on WRS is relatively limited. Under tension loading, the maximum stress occurs near the weld. The ends of the weld enter the yielding state later than the middle part of the weld due to the distribution of the WRS. As the weld angle increases and the length of the weld increases, the stress in the weld zone decreases, while the stress in the base material zone correspondingly increases. In addition, CFRP strengthening can reduce the magnitude of stress. This study provides preliminary references for understanding the tensile behavior of CFRP-strengthened welded steel plates with inclined welds.

This study aims to compare the influence of residual tensile and compressive stresses resulting from welding on the fatigue crack propagation. The development of fatigue fractures within zones characterized by residual tensile and compressive stresses is investigated using numerical simulations. A quantitative evaluation of the impact of residual stresses on the crack propagation is conducted by comparing the crack opening loads in cases with and without residual stresses. A series of comparative analyses of crack closure parameters is performed to examine the effects of changes in the load level (e.g., load ratio, maximum load, and overload ratio) on the release and redistribution of welding residual stresses. The research findings indicate that the influence coefficients for residual tensile stress and compressive stress on the fatigue crack propagation are 0.65 and 1.5, respectively. Increasing the cyclic loading amplitude and overloading are beneficial for reducing the difference in crack closure parameters between cases with residual stress and those without, weakening the influence of welding residual stress on the crack growth.

The welding process, incorporating rapid heating and cooling, generates distortion and residual stress in weldments. Welding distortion and residual stress in welded structures can result in problems such as dimensional inaccuracies during assembly and raise concerns regarding safety during service. Therefore, accurate prediction and reduction of residual stress are critical in improving the quality of a weldment. In the present paper a new method of analysis is proposed to predict welding residual stress by considering solid phase transformations during the welding process. This method is applied to two cases, involving medium carbon steel and low carbon steel respectively. The analysis of medium carbon steel revealed the presence of compressive residual stress due to martensite formation when phase transformation was considered. However, in low carbon steel the residual stress obtained considering the effect of phase transformation did not differ significantly from that obtained when phase transformation was ignored.

Residual stress in welded joints by using a new weld metal with the property of low-temperature phase transformation is numerically analyzed. 10 % Nickel and 10 % Chromium are involved in the developed welding material for producing the property of martensitic phase transformation at a low temperature and for generating compressive residual stress. A fillet-welded joint between plate and stiffener is used for the numerical simulation of the thermal elastic-plastic finite-element analysis with coupling phase transformation effect. Moving heat source is considered by using the gradual deposition of the finite-element during welding process. Distribution of the computed residual stress mostly agrees with the measuring values by strain gauge. Compressive residual stress distributes in the weld metal for both longitudinal and transverse directions with weld line. The effects of the material of weld metal and welding pass sequence on residual stress are then investigated. Residual stresses on the weld toe and root are improved lower by using the low-temperature transformation weld wire than the conventional one, regardless of the sequence of welding deposition. It is found that the weld metal with property of low-temperature phase transformation is effective to reduce residual stress near weld metal.

Electron beam welding (EBW), pulsed Nd:YAG laser beam welding (P-LBW), and pulsed tungsten inert gas (P-TIG) welding of Ti–5Al–2.5Sn alloy were performed in order to prepare full penetration weldments. Owing to relatively high power density of EBW and LBW, the fusion zone width of EBW weldment was approximately equal to P-LBW weldment. The absence of shielding gas due to vacuum environment in EBW was beneficial to the joint quality (low oxide contents). However, less cooling rates were achieved compared to P-LBW as an increase in heat-affected zone width and partial α′ martensitic transformation in fusion zone were observed in EBW weldments. The microstructure in fusion zone in both the EBW and P-TIG weldments comprised of both acicular α and α′ martensite within the prior β grains. Hardness of the fusion zone in EBW was higher than the fusion zone of P-TIG but less than the fusion zone of P-LBW weldments due to the observed microstructural differences. Notch tensile specimen of P-LBW showed higher load capacity, ductility and absorbed energy as compared to P-TIG and EBW specimens due to the presence of high strength α′ martensite phase. Maximum sheet distortions and tensile residual stresses were observed in P-TIG weldments due to high overall heat input. The lowest residual stresses were found in P-LBW weldments, which were tensile in nature. This was owing to high power density and higher cooling rates in P-LBW operation. EBW weldment exhibited the highest compressive residual stresses due to which the service life of EBW weldment is expected to improve.

Fusion welding induces sudden thermal alteration in the small weld region which leads to residual stresses and deformations in the weld joint under the effect of surrounding constraints of parent metal. These residual stress becomes more complex in thick plate weld joints. In the current study, an in-process mitigation technique has been suggested and FE modelled for a thick AISI 304 steel plate submerged arc welding. A static heat sink source and a transient side heating source were employed as a combined thermal tensioning unit. In FE modelling, a 3D volumetric heat source (welding), element birth and death technique, surface heat source (side heating), high convection heat coefficient (heat sink) and temperature dependent material properties were incorporated. The effect of individual thermal tensioning source, side heating location, intensity of heat sink and combined heat sink and side heating were analysed for welding induced residual stresses and deformation. It was observed that transient side heating process diminishes the cooling rate of the weldments and also reduces the thermal gradient which elevates the compressive residual stress distribution in the heating region to tensile nature. This sudden lift in stress values from compressive to tensile omits the abrupt change in residual stress distribution across the weld centreline which leads to less deformation of the weld plate. Similarly, the heat sink process was observed to decrease the peak temperature in the region away from welding torch. The lower peak temperature induces tensile stress during the welding which decreases the overall compressive residual stress in the region. Hence, the overall peak of the residual tensile stress in the FZ gets decreased. It is observed that the combined heat sink and side heating process is an effective in-process mitigation method to control residual stress distribution in thick plate welding.KeywordsWeldingResidual stressComputation modellingMitigation technique

The fabrication of structural member using dissimilar steels renders steel structures lighter and more economical. However, it always involves welding process and produces different residual stresses in welds as compared with welding of similar steels. This paper presents the characteristics of residual stresses in welds of similar and dissimilar steel weldments by carrying out three-dimensional (3-D) thermal elastic-plastic finite element (FE) analysis. The materials used in this investigation were SM400, SM490, SM520 and SM570, widely used structural steels in welded structure. Results show that the maximum longitudinal residual stresses in welds of the similar steel weldments increase with increasing yield stress of the steel welded (SM400 < SM490 < SM520 < SM570). In case of the dissimilar steel weldments, the difference between the longitudinal residual stresses in welds increases with increasing yield stress of the steel welded together with SM400 (SM490 < SM520 < SM570).

Fatigue strength of welded joints is improved by inducing compressive residual stress at weld toes. The ultrasonic impact treatment (UIT) is regarded as an effective method for inducing compressive residual stress at weld toes. However, excessive loads that cause plastic deformation at weld toes relieve the induced compressive residual stress. In addition, stress fluctuation affects the relaxation of residual stress even it is smaller than the yield strength. The relaxation of compressive residual stress decreases the fatigue strength improvement. Therefore, in order to evaluate the fatigue strength of welded joints enhanced by UIT, it is necessary to quantify the relaxation of local residual stresses at weld toes under cyclic loading. In this study, we measured a residual stress at the UIT groove using the X-ray diffraction method with a small-diameter collimator and an irradiation angle that was corrected based on the shape effect of the UIT groove, and we investigated its relaxation behavior under cyclic loading. In addition, we estimated the fatigue test results of the out-of-plane gusset joints improved by UIT using the modified Goodman diagram considering the relaxation of residual stress.

T-joint welding is the most common type used in heavy equipment industry. Localized heating and subsequent cooling induce residual stress in the weld process. Service loading overlapped with residual stress influences the strength of the welded structure and leads to premature failure of structure. In this study, finite element analysis is used to study the influence of welding groove on residual stress and distortion in T-joint welding. The simulation consists of sequentially coupled thermal and elastic-plastic analysis using an element birth and death method to model the addition of weld metal to the workpiece. The results of numerical simulation are verified by comparing with experiment from published literature. The results show that welding groove has a significant influence on welding residual stress.