Longitudinal Residual Stress Research Articles

Residual stress analysis, microstructural characterization, and mechanical properties of tungsten inert gas-welded P92/AISI 304L dissimilar steel joints

In the present work, the creep strength-enhanced ferritic martensitic P92 steel was welded with 304L austenitic stainless steel. The dissimilar joining of these two different grades of material was performed by using tungsten inert gas welding process. The nickel-based ERNiCr-3 welding consumable was used. The influence of post-weld heat treatment (760 °C, 2h), called as tempering, was also investigated. The secondary electron and optical image confirmed that ERNiCr-3 weld metal is accompanied by an equiaxed austenitic microstructure with Ni weight percentage of 68.29%. The energy-dispersive X-ray spectroscopy and electron probe microanalyzer results of the weld fusion zone revealed the Nb, Cr, and Ti segregation in the inter-dendritic region. The elemental mapping of the carbon-depleted zone, and the interface was performed using an electron probe microanalyzer, which revealed the diffusion of Ni, Cr, and Fe across the interface of P92 steel and ERNiCr-3 filler weld. The tensile test result indicated that part of the dissimilar weld joints (DWJs) with relatively weak ultimate tensile strength was ERNiCr-3 weld metal. The ultimate tensile strength value of the DWJs was observed as 610 MPa and 580 MPa in the as-weld and post-weld heat treatment situations, respectively. The Charpy V-notch impact energy of the ERNiCr-3 weld fusion zone was achieved as 135 ± 2 J and 140 ± 2 J in as-weld and post-weld heat treatment situations, respectively. The low impact toughness of the ERNiCr-3 weld metal was attributed to the presence of niobium carbide (NbC) and titanium carbide (TiC) particles. The peak longitudinal residual stress of 490 MPa and transverse residual stress of 442 MPa were noted in the ERNiCr-3 weld fusion zone at a depth of 3 mm from the top surface. The tempering heat treatment exhibited a significant drop in the residual stresses value for the weld fusion zone and heat affected zone (HAZ).

Residual stress and material flow prediction in Friction Stir Welding of Gr2 Titanium T-joints

Friction Stir Welding is nowadays an established technique successfully used by many industries. However, most of the research and, consequently, most of the applications regard aluminum alloys and butt joints. T-joints are of high interest for different industrial sectors as aeronautical, aerospace, naval and ground transportation, for which joint integrity and low residual stress are extremely important. In this study, an experimental and numerical approach is proposed with the aim to study the peculiarities of the residual stress distribution and material flow occurring in FSW of CP-Ti T-joints. Experiments were carried out to assess the feasibility of the process and to acquire the temperature data needed for the validation of a specifically set-up numerical model. Peculiar numerical strategies have been defined in order to calculate the residual stress with affordable CPU time and to highlight the bonding surface between the skin and the stringer. Main findings include a longitudinal residual stress profile different from the one usually found for butt joints. The reasons for this behavior were explained through a deep investigation on the temperature distribution in space and evolution in time. Finally, the bonding surface between skin and stringer was highlighted together with the possibility of flow defects in the fillet area.

Investigation of welding temperature field and residual stresses of corrugated steel web girders

This paper proposes a new approach for obtaining the welding temperature field and stress distribution in a corrugated steel web girder. This approach was validated by comparing the control temperatures (obtained from finite element modelling of CO2 gas shielded welding) of a corrugated steel web girder with experimental findings. Moreover, the effects of different welding speeds on welding residual stress were analysed. The control point temperatures obtained using modelling corresponded closely with those of the observed data. The welding residual stress was primarily affected by the longitudinal residual tensile stress and increased as the distance to the weld decreased. The welding speed had an insignificant effect on the residual stress distribution but a significant effect on the residual stress peak. The findings of this study can serve as a reference for the analysis of the welding temperature and stress fields of corrugated steel web girders.

The effect of oscillating capping TIG welding on residual stresses of 2219-T8 butt joint

Oscillating capping TIG welding (OCW) was proved valid to increase joint properties of the 2219-T8 aluminium alloy. Its effects on the welding residual stresses (WRS) should also be clarified. In this study, the residual stresses of the 2219-T8 plate butt welding of capping welding (CW) + OCW and CW technologies were investigated by simulation and experiment. The results showed that OCW reduced the peak value of the tensile longitudinal residual stress (LRS) in the joints. And its mechanism was discussed. Differences in bead geometry, heat input and number of welding passes of OCW affected LRS. Among them, wide bead geometry resulted in lower residual plastic strain, thus decreasing LRS peak value in a great manner.

Quality index for friction stir welds in 7050 aluminum plates

AA7050-T7451 is a heat-treating aluminum alloy with high mechanical strength, ideal for producing lightweight structural components. Common types of welding lead to structural changes in the material that could decrease their mechanical properties affecting the fatigue life of the joints; however, a solid-state process known as friction stir welding (FSW) have been increasingly used as an alternative solution to reduce these severe effects. This work attempts to study the FSW behavior over 7050-T7451 aluminum alloys through the characterization of the resulting residual stresses and propose a manufacturing quality index based on their magnitude and distribution. An ultrasonic method employing longitudinal critically refracted (LCR) waves was used to determine the longitudinal residual stresses at different distances from the centerline in plates welded with different parameters.The resulting stress distribution is consistent with the literature review, presenting maximum values around 200 MPa at the center of the weld. A quality index was calculated through the average of all stresses in that region. It was found that higher residual stresses are produced with higher traverse and rotational speed (400 mm/min and 908 RPM). Therefore, to improve the process regarding the level of residual stresses, it is recommended to use lower welding tool velocities.

Distribution characteristics of residual stresses in typical wall and pipe components built by wire arc additive manufacturing

It is of great importance to thoroughly understand residual stress distribution in wire arc additive manufacturing (WAAM) and its relationship with the deposition variables. In this study, stainless steels 308LSi and 304 were used as WAAM feedstock and substrate, respectively, for additive manufacturing of two typical structures, namely wall and pipe structures. A thermomechanical coupling analysis model for WAAM was developed to investigate the formation mechanism of residual stresses in both structures, and their relationship with the deposition height and shape. The validity of the analysis was evaluated by comparing the simulated residual stresses with those measured by the contour method. Regardless of the wall or pipe structure, the tensile longitudinal (or circumferential) residual stress exists on the WAAM top surface and has the largest value (~300 MPa) at the position of several layers below the top surface. The distribution pattern of the longitudinal (or circumferential) residual stress is tensile in the layers near the top surface, compressive in the layers near the substrate surface, and tensile near the bottom surface of the substrate. This distribution pattern reaches a quasi-stable state when the total deposition height is greater than a certain size (~10 mm and 15 mm for wall and pipe structures, respectively). For the pipe structure, however, the residual stress distribution is not symmetric along the height direction. This analysis model can provide guidance for effective tailoring of residual stresses in WAAM components.

Prediction of Residual Stress Distribution in NM450TP Wear-Resistant Steel Welded Joints

This study developed a thermo-metallurgical-mechanical simulation method to calculate the temperature field and residual stress distribution in the NM450TP wear-resistant steel welded joints. During the simulation, the solid-state phase transformation and softening effect of NM450TP wear-resistant steel was considered. The simulation results were compared with the experimental results, which verified the feasibility of this method. The influences of solid-state phase transformation and softening effect on the welding residual stress distribution were discussed. The numerical simulation results showed that the solid-state phase transformation had a more significant effect on the magnitude and distribution of the longitudinal residual stress than that of the transverse residual stress. The softening effect had a significant influence on the peak value of the longitudinal residual stress and had little influence on the transverse residual stress. Comparing the numerical simulation results with the experimental results, it could be seen that the calculation results of the welding residual stress were in the best agreement with the experimental measurement results when the solid-state transformation and softening effects were considered at the same time.

Residual stress influence on fatigue crack propagation of CFRP strengthened welded joints

In order to take into account the influence of welding residual stresses on fatigue crack growth, thermo-elastic-plastic finite element models of steel cruciform welded joints were developed by the ABAQUS software. The distribution and magnitude of longitudinal and transverse residual stresses were obtained in consideration of different welding currents and speeds. Uniaxial tensile fatigue tests on cracked cruciform joints strengthened with carbon fiber reinforced polymer were conducted. The coupling actions of residual stresses and fatigue loads were applied to subsequently simulate fatigue crack propagation via using the Extended Finite Element Method. Good agreement between the simulated and theoretical transverse residual stresses at the weld toe along the plate thickness direction verifies the accuracy of numerical results. The welding speed has a greater impact on residual stresses than the welding current. The stiffness ratio of carbon fiber reinforced polymer and steel plate is larger, and a better reinforcement effect will be achieved. Whether specimens repaired or not, it significantly decreases the fatigue life of cracked welded joints in the presence of residual stresses, but the fatigue crack growth trajectory is almost unchanged.

Influence of ultrasonic impact treatment on microstructure and mechanical properties of nickel-based alloy overlayer on austenitic stainless steel pipe butt girth joint

Ultrasonic impact treatment (UIT) is carried out on the Ni-based alloy stainless steel pipe gas tungsten arc welding (GTAW) girth weld, the differences of microstructure, microhardness and shear strength distribution of the joint before and after ultrasonic shock are studied by microhardness test and shear punch test. The results show that after UIT, the plastic deformation layer is formed on the outside surface of the Ni-based alloy overlayer, single-phase austenite and γ type precipitates are formed in the overlayer, and a large number of columnar crystals are formed on the bottom side of the overlayer. The average microhardness of the overlayer increased from 221 H V to 254 H V by 14.9%, the shear strength increased from 696 MPa to 882 MPa with an increase of 26.7% and the transverse average residual stress decreased from 102.71 MPa (tensile stress) to −18.33 MPa (compressive stress), the longitudinal average residual stress decreased from 114.87 MPa (tensile stress) to −84.64 MPa (compressive stress). The fracture surface has been appeared obvious shear lip marks and a few dimples. The element migrates at the fusion boundary between the Ni-based alloy overlayer and the austenitic stainless steel joint, which is leaded to form a local martensite zone and appear hot cracks. The welded joint is cooled by FA solidification mode, which is forming a large number of late and skeleton ferrite phase with an average microhardness of 190 H V and no obvious change in shear strength. The base metal is all austenitic phase with an average microhardness of 206 H V and shear strength of 696 MPa.

Influence of strain-hardening models and slopes on the predicted residual stresses in structural steel S235 weldments

The objective of this research is to systematically understand how strain-hardening models and phase- and temperature-dependent strain-hardening slopes affect the computed residual stresses in single-pass welded joints made of the widely used structural steel S235. Both experimental methods and numerical simulation have been utilized for investigation. The results reveal that the material plasticity model has a massive effect on the predicted welding residual stresses (WRS). The calculated magnitude of WRS in the base metal (BM) adjacent to the weld zone inside the plate is largest when the isotropic hardening model is used, while it is smallest applying the kinematic hardening model. The comparison of predictions with measurements shows that the isotropic hardening model can predict WRS more accurately for S235 steel. The change in the temperature-dependent strain-hardening slopes of the generated phases (austenite and bainite in this case) have practically no impact on the predicted WRS. The calculated longitudinal residual stress (LRS) amount in BM nearby the weld zone is highly sensitive to the applied strain-hardening slopes of the initial microstructure (ferrite here), while that of transverse residual stress (TRS) is not. In contrast to the strain-hardening slopes of the initial microstructure at elevated temperatures, that at room temperature plays a crucial role in the simulated LRS. In this study, guidance is provided on how the phase- and temperature-dependent strain-hardening slopes of a specific steel can be determined economically and reliably in numerical welding simulation.

A Study on the Thermo-Mechanical History, Residual Stress, and Dynamic Recrystallization Mechanisms in Additively Manufactured Austenitic Stainless Steels

In this work, both numerical simulations and experimental characterization were used to obtain a broad understanding of the thermo-mechanical history, residual stress, and microstructure of the directed energy deposition (DED) process of austenitic stainless steels. To investigate the effect of process factors on residual stress, the global sensitivity analysis approach based on D-MORPH-HDMR was utilized. The results of the research reveal that the amplified effect of the influence of the three input variables (layer thickness, L; laser power, P; and scanning speed, v) on the transverse residual stress and thickness-direction residual stress is L > P > v; in contrast, the influence of longitudinal residual stress is P > L > v. We also found that general tendencies in local plastic strain accumulation are analogous to the relative distribution of geometrically necessary dislocations (GNDs). Additionally, we investigated post-solidification structures connected to residual stress, such as submicron dislocation cells and dynamic recrystallization (DRX) in austenitic stainless steels during DED. The investigation revealed that the DDRX and CDRX phenomena were caused by the bulging of initial grain boundaries and progressive sub-grain rotation (PSR). The fact that the sample bottom had more thermo-mechanical cycles than the top led to a higher dislocation density and hence more DDRX. This study presents a unique perspective on the link between residual stress and microstructure in additive manufacturing.

A global thermo-mechanical model to mitigate welding residual stress and deformation in production of an aluminum bio-inspired AUV with a curved outside corner joint

Welding mechanics of large-scale complex-shaped structures is generally either disregarded or implicitly presumed due to high complexity and time consumption — even in the case of numerical analysis, typically it is limited to local thermo-mechanical models of straight butt or tee welded joints. Nevertheless, not only is this study aimed at presenting a time-saving global thermo-mechanical model of a curved outside corner joint but also at exploiting combined effects of welding parameters to mitigate deformation and residual stress. The global thermo-mechanical model is thereby constructed by combination of shell and solid finite elements providing Thermal-Elastic-Plastic (TEP) analysis for an aluminum Autonomous Underwater Vehicle (AUV) of which novel hull shape inspired by catfish morphology results in a longitudinal curved outside corner welded joint. A suitable polynomial mathematical function enabled the welding heat source to move steadily along the curved path of the joint. Saving up computational time 3.5 times greater than conventional full 3D method, the global shell/3D TEP FEM is validated well against experimental temperature, distortion and residual stress distributions when locating the boundary between shell and solid elements with the size of solid zone up to the 3 times thickness of base metal based on accuracy of molten metal penetration, deformation and residual stress prediction. A stark difference of about 120% in maximum amount of longitudinal residual stress is observed between global and local models. Finally, optimal outcomes are employed in production of the AUV so that 33% reduction in welding speed mitigated residual stress by 22% whereas welding length and sequence were more effective on distortion.

Numerical simulation of welding deformation and residual stress in aluminum alloy plate-to-sleeve welded joints

The plate-to-sleeve welded joint is employed in the aluminum alloy spatial structure. The welding deformation and residual stress determine the dimensional accuracy and even increase the failure risk. Based on ABAQUS software and the coordinate transformation method, a finite element model with the arc weaving was developed to investigate the temperature field, welding deformation, and residual stress of an AA6061-T6 plate-to-sleeve welded joint with 8-pass. The metal inert gas welding experiment was performed with the corresponding joint, and the welding deformation and residual stresses were measured to verify the numerical results. The results show that the thermal cycle of the weaving weld and its vicinity have multiple peaks, and the time interval between two adjacent peaks is one weaving period. The deformation pattern of the joint is angular deformation. The maximum deformation is observed in the weld toe of the top surface. The longitudinal residual stress in the weld and its vicinity is high tensile stress, and that in the upper part of the sleeve is mainly compressive stress. The transverse residual stress in the weld and its vicinity of the top surface is low tensile stress, and that in the bottom surface is compressive stress. Furthermore, the evolution of the welding deformation and residual stresses attributed to subsequent weld passes was elaborated, which provides a reference for developing control schemes.

Effects of biaxial residual stress components on mixed-mode fatigue crack propagation behavior in friction stir welded 7075-T6 aluminium alloy panel

Residual stress in friction stir weld (FSW) joint significantly affects fatigue performance. It can often combine critically with the applied load cause premature fatigue failure. Research on the residual stress effects on fatigue behavior is required to assess the damage tolerance issues in FSW joints. In this study, the effect of biaxial residual stress components (longitudinal residual stress and transverse residual stress) on mixed-mode crack propagation behavior in FSWed 7075-T6 fuselage panel was studied. Residual stress profiles across the welded plate were measured by X-ray diffraction technique. Fatigue crack propagation for mode mixity angles of 30°, 45° and 60° were carried out. The stress intensity factors (SIFs) at the crack tip were evaluated by finite element method and used to study the effect of biaxial residual stress and the individual component on mixed-mode crack behaviors. The results show that the variation of crack path is strongly linked with the residual stress component as well as the initial oblique crack angle. SIF components are affected by the individual residual stress component. Both two components are required to study the mixed-mode crack propagation in FSWs.

Influence of Energy Ratio of Hybrid Heat Source on Residual Stress Distribution of 7A52 Aluminum Alloy VPPA-MIG Hybrid Welding

Variable Polarity Plasma Arc-Metal Inert Gas (VPPA-MIG) welding process is a new hybrid welding process with broad application prospects for aluminum alloy structure in the fields of aerospace manufacturing, transportation and others. The heat source of the hybrid welding process is composed of VPPA heat source and MIG heat source. When the total input energy of VPPA-MIG hybrid heat source is constant, the different energy ratio of VPPA arc and MIG arc affects not only the forming effect of hybrid weld, but also the stress distribution of hybrid welding joint. Hole-drilling method was used to analyze the influence of the ratio of VPPA and MIG arc energy on the distribution of welding residual stress in the process of 10 mm 7A52 aluminum alloy VPPA-MIG hybrid welding. The results show that the peak magnitude of hybrid welding residual stress increases with the increase of the ratio of VPPA arc energy. Considering the appearance of weld forming, VPPA-MIG hybrid welding parameters of 7A52 aluminum alloy are optimized on the basis of the distribution characteristic of residual stress. When the ratio of VPPA arc energy is selected between 35% and 40%, the peak magnitude of transverse residual stress is (in the direction vertical to the weld) no more than 92.0 MPa, and the peak magnitude of longitudinal residual stress(in the direction parallel to the weld) is no more than 234.3 MPa. It shows that the VPPA-MIG hybrid welding with optimized parameters can not only produce weld joint with satisfied macroscopic appearance, but also avoid high peak magnitude of residual stress.

Residual Stress Reduction with the LTT Effect in Low Carbon Manganese-Steel through Chemical Composition Manipulation Using Dissimilar Filler Material in Laser Beam Welding

This paper investigates the manipulation of chemical composition of a laser weld by dissimilar filler material and its effect on residual stress. The aim is to minimize residual stresses in the weld seam. In order to negate residual stresses, dissimilar combinations of low-carbon manganese steel (S235JR) base material with high-alloyed solid filler wires (G19 9 and G25 20), as well as similar combinations with low-alloyed solid filler wire G3Si1 are analyzed. The goal of the paper is to show that the so-called low-transformation-temperature effect can be used to induce residual compressive stresses in a weld without the use of specially manufactured filler wires. Chemical compositions are generated within a laser-beam-welding process by means of dilution, proving that the concept of in situ alloying is usable in order to affect the martensite formation on a weld. Dilatometry measurements show that a varying Cr and Ni content in a weld reduces the phase-transformation temperature and increases dilatation. EBSD analysis indicates that a fully martensitic weld with a negligible amount of retained austenite is created while the base material preserves its ferritic-pearlitic microstructure. Residual stress measurements with the hole-drilling method demonstrate a reduction in longitudinal tensile residual stresses, whereby the magnitude of the induced residual compressive stresses depend on the Ms temperature. As a result of this research, it was proven that a reduction in tensile residual stress by means of targeted alloying with conventional materials in low-carbon manganese steel is possible. Under the experimental conditions, residual stress in the weld seam could be reduced to 0 MPa. In some cases, even compressive residual stress in the weld could be achieved.

Accurate evaluation on residual stress considering solid-state phase transformation and initial stress in thick weld

During the welding process of thick plates, it is difficult to evaluate the residual stress distribution in thick welds accurately because complicated residual stress is generated by multi-thermal cycles. In this study, a multi-pass butt joint was fabricated using Q690 high strength steel with the thickness of 75 mm, meanwhile experiments were carried out to characterize the microstructure and measure the through-thickness distribution of longitudinal residual stress in a butt-welded joint by the contour method. Then numerical methods were developed to predict the through-thickness distribution of residual stress in butt-welded joints. To evaluate residual stress accurately and efficiently, the effects of solid-state phase transformation (SSPT) and initial stress were taken into consideration, and the parallel computation technology and iterative substructure method were employed. The root-mean-square error (RMSE) was employed to evaluated the prediction accuracy of numerical methods between measurement and numerical results of residual stress. Through comparing the simulated results with experimental data, the validity of the developed numerical methods was verified. Numerical results indicate that the through-thickness distribution of residual stress in butt-welded joints is very complex and peak value of tensile stress can be found in the area adjacent to the heat-affected zone (HAZ). Moreover, the RMSE is significantly decreased from 307 to 8 when considering the effect of SSPT on residual stress in weld vicinity, and the RMSE is apparently decreased from 137 to 11 when considering the effect of initial stress on residual stress in base metal.

Buckling distortion investigation during thin plates butt welding with considering clamping influence

Welding induced buckling is generally considered as the most complicated type of out-of-plane welding distortion during thin plate section fabrication, which will significantly influence the fabrication accuracy and cost. Thin plates of 3 mm thickness with dissimilar materials were experimentally butt welded together beforehand, while clamping constraint by fixture jig and additional plate was employed. After cooling down and clamping release, out-of-plane welding distortions were measured, and characteristic of welding buckling behavior can be observed. Advanced thermal elastic plastic (TEP) FE computation with solid elements models of examined butt-welded joints were then carried out. Welding induced buckling can be represented without considering clamping constraint, while much larger difference between computed results and measurement data was obtained. When the influence of clamping constraint employed during welding experiment was considered, good agreement for both deformed tendency and magnitude of out-of-plane welding distortion can be represented. With the clarification of mechanism based on the comparison of longitudinal residual stress, plastic strain as well as shrinkage force, clamping can significantly reduce magnitude of out-of-plane welding distortion, which still could not avoid the occurrence of welding induced buckling, as well as the change of deformed shape pattern.

Study of Residual Stress Evolution in SUS304/Q235 Bimetallic Clad Plate Butt-Welded Joints Considering Welding Sequence

Abstract Residual stress prediction and controlling is important for structural integrity assessment of weldments. In this work, finite element (FE) and experimental methods were integrated to study the influence of welding sequence on the SUS304/Q235 bimetallic clad plate (BCP) joints during multilayer and multipass welding. The results show that the peak residual stress values on flyer plate surface are weakly affected by welding sequences but the width of high surficial longitudinal stress area of joint with base layer welded first is bigger. Meanwhile, welding sequence has a great influence on the longitudinal residual stress evolution law inside joints. When base seam layer is welded first, the highest stress concentration appears in the transition layer. However, it would be transferred into the first base seam layer due to martensite phase transformation when flyer seam layer is welded first. Residual stress controlling in the BCP joint should attract more attention from researchers.

Influence of welding current on the microstructure, mechanical properties, residual stresses, and nano-mechanical behavior of tungsten inert gas-welded dissimilar joints of Inconel 625 and Incoloy 800

In the present work, Inconel 625 and Incoloy 800 thin sheets were TIG-welded without using fillers and at three different welding currents (40 A, 50 A, and 60 A). The influence of variation in welding currents on various characteristics of the weldments was investigated using various characterization techniques. Weldments obtained at 60 A showed the highest tensile strength and plastic deformation due to the formation of cellular dendritic microstructure in the fusion zone. Observation of the fractured surfaces revealed ductile nature for all the weldments. In addition, impact tests were performed at 25°C, 150°C, and 250°C, and the results indicated that with the rise in temperature, impact toughness decreased due to coarsening of carbides at grain boundaries in all the weldments. Furthermore, impact properties and hardness of weldments were also affected owing to the differences in interdendritic spacing and grain size. Weldments obtained at 40 A depicted higher nanohardness, whereas 50 A weldment showed relatively greater pileup height as compared to other weldments. Moreover, 60 A weldments showed highest longitudinal and transverse residual stresses due to relatively higher volumetric changes.