Peak Tensile Residual Stress Research Articles

Influence of laser shock peening on Residual stress and microhardness of AA2219 friction stir weld

This work focuses on the effect of Laser Shock Peening (LSP) on residual stress (RS) and microhardness of AA2219 T87 Friction Stir Weld (FSW). FSW plate was laser peened, covering all the regions of the weld and RS measurement was carried out before and after peening. RS distribution across the weld is non-uniform, and the profile is M shaped with tensile RS near to weld center and compressive RS away from the center. The maximum tensile RS is + 123.5 MPa and + 96.7 MPa on the top and bottom surfaces, respectively. LSP has reversed the tensile RS to compressive with a single pass of peening, and the subsequent passes increased the compressive RS further. Peak tensile RS changes to compressive RS of −20 MPa, −130.2 MPa, and −195.5 MPa with single, three and six passes of peening, respectively, on the top surface. It is due to plastic deformation and strain-hardening effect induced on the surface during LSP. An increase in hardness due to LSP on the surface and subsurface levels is noticed, and increased number of passes affected higher depth.

Rapid calculation of part scale residual stress – Powder bed fusion of stainless steel, and aluminum, titanium, nickel alloys

A novel analytical model is developed to compute the part scale through-thickness longitudinal residual stress distributions and applied for laser powder bed fusion of four commonly used powder alloys. An important input for the analytical modeling calculations is the peak residual stress for a deposited layer, which is estimated using a unique functional relationship and presented as a function of important process conditions for laser powder bed fusion of different powder alloys. The analytically calculated results of longitudinal residual stress distributions through the part and baseplate thickness are tested rigorously with the corresponding numerically computed and experimentally measured results in the literature for laser powder bed fusion of small and large parts involving the deposition of several thousands of layers. It is shown further that the analytical model can serve as a fast and practical design tool to estimate the through-thickness longitudinal residual stress distribution, which is along the length of the part, for part scale laser powder bed fusion using inexpensive computational resources and with appreciable accuracy. The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations. • An analytical model for residual stresses in 3D printed parts is extensively tested. • The model is validated with experimental data and numerically computed results. • Residual stresses in large 3D printed parts of 5 alloy compositions were examined. • Powder-specific process maps of peak tensile residual stresses are presented.

Coupled Eulerian-Lagrangian model for residual stress prediction in orthogonal cutting of Waspaloy

Residual stress is one of the most critical factors of machined surface integrity, which directly determines corrosion resistance and fatigue life of components. Therefore, it is necessary to accurately predict the machining-induced residual stress, especially for critical aerospace parts. In this paper, a finite element model based on the Coupled Eulerian-Lagrangian method is employed to predict the residual stress in orthogonal cutting of Waspaloy material under different cutting conditions. The depth profiles of residual stress along the cutting speed direction are determined using the X-ray diffraction and electropolishing techniques. The results show tensile residual stresses at the cutting speeds of 64 m/min and 86 m/min with 100 microns uncut chip thickness. The depth at the machined surface influenced by the residual stress is identified and compared from both simulations and experiments. The simulated cutting forces and residual stress distributions from the finite element model are compared with the experimental results to validate the model. In addition, the microstructure property at the machined surface is examined to determine the depth of plastic deformation layers. White layers are identified at the higher cutting speed, and it is shown that the formation of white layers is directly related to the location of the peak tensile residual stress.

On the role of input welding parameters on the microstructure and mechanical properties of Al6061-T6 alloy during the friction stir welding: Experimental and numerical investigation

The Taguchi method was employed to find the optimum values of friction stir welding parameters including welding speed, rotating speed, and tilt angle for joining AA6061-T6 aluminum alloys. The combined influences of these parameters were entirely analyzed. Statistical outcomes were investigated by the study of variances and signal-to-noise ratios. A Coupled Eulerian and Lagrangian technique is implemented to simulate and verify the optimal parameters during the friction stir welding. To verify results, a comparison between the welding process under optimized parameters with experimental and non-optimized parameters was simulated for the friction stir welding process. The material flow, strain rate, thermal behaviors, and mechanical properties of samples fabricated with optimal welding parameters are higher than those produced from the non-optimal parameters. It was also concluded that the grain size of the stir zone under optimal welding parameters (6–8 µm) is finer than that of non-optimal welding parameters (11–13 µm). Low uniform distribution of material element and coarse microstructure were some of the results of welding with non-optimized parameters. Based on residual stress analysis, the application of optimal joining conditions can decrease the peak tensile residual stress by about 38.3%. The much desirable results obtained in terms of microstructure and mechanical properties could be of great significance to the welding industry.

Computation of residual stresses, distortion, and thermogravimetric analysis of Inconel 625 weld joints

In the current investigation, Inconel 625 weld joints were fabricated by Activated tungsten inert gas (A-TIG) and Tungsten inert gas (TIG) welding techniques. The joint configurations employed square butt and V groove edge preparations. Residual stresses measurement was carried out by X-ray diffraction using the Proto iXRD measurement system. Distortion in weld joints was estimated by measuring the vertical displacement on the grids marked on the weld joints before and after welding by using an electronic height gauge. Weldment revealed distinctive microstructure, peak tensile residual stress, and angular distortion. A-TIG weld joint exhibited lower residual stresses and distortion compared to the TIG weld joint. Thermogravimetric analysis (TGA) has inferred that the fusion zone of A-TIG and TIG weldments revealed better hot corrosion resistance at high temperatures.

Effect of preheating and post heating in reducing diffusible hydrogen content and hydrogen assisted cracking susceptibility of modified 9Cr–1Mo steel

The hydrogen assisted cracking susceptibility of Modified 9Cr–1Mo steel weld is evaluated by implant test by determining lower critical stress for different preheating and combination of pre, post heating conditions. The diffusible hydrogen present in the implant specimens for different test conditions is estimated. Residual stress distribution in the weld for different heating condition is estimated using SYSWELD software. For a combination of pre + post heating at 200°C, the diffusible hydrogen content of the weld comes down to 1.17 from 4.7 mL/100g and the lower critical stress of the implant specimen increases from 250 to 370 MPa. Preheating + post heating also brings down the peak tensile residual stress level in the weld joints and lowers the cracking susceptibility.

Material properties and membrane residual stresses of S690 high strength steel welded I-sections after exposure to elevated temperatures

This paper reports a thorough experimental investigation into the material properties and membrane residual stresses of S690 high strength steel welded I-sections after exposure to seven levels of elevated temperatures ranging from 30 °C (room temperature) to 950 °C. The experimental programme included heating, soaking and cooling of S690 high strength steel coupons and welded I-section specimens as well as post-fire material tensile coupon tests and membrane residual stress measurements, with the experimental rigs, procedures and results fully reported. The key post-fire material properties were then carefully analysed together with the test data collected from the existing literature, and a new set of retention factor curves of simple multi-linear shapes was proposed and shown to result in accurate predictions of post-fire yield and ultimate stresses for S690 high strength steel after exposed to elevated temperatures. Regarding post-fire membrane residual stresses, the measured distribution pattern and peak amplitudes in S690 high strength steel welded I-section after exposed to an elevated temperature of 300 °C generally remained unchanged in comparison with those in S690 high strength steel welded I-section at room temperature. However, for higher elevated temperatures ranging from 600 °C to 950 °C, the peak values of both compressive and tensile membrane residual stresses dramatically decreased, and moreover the discrepancy between the peak compressive and tensile membrane residual stress values became smaller and the transition regions (where the peak tensile residual stresses are changed to the peak compressive residual stresses) became narrower; this can be attributed to the fact that prominent elastic strain redistribution and residual stress relaxation of steel starts from around 500 °C–600 °C. A membrane residual stress predictive model was proposed for S690 high strength steel welded I-sections after exposed to elevated temperatures, and shown to well represent the measured membrane residual stress patterns and amplitudes over the full temperature range from 30 °C to 950 °C.

The Effect of Martensitic Transformation on the Evolution of Residual Stresses and Identification of the Critical Linear Mass Density in Direct Laser Metal Deposition–Based Repair

Abstract Direct laser metal deposition (DLMD) is a promising additive manufacturing technique which has a huge potential in remanufacturing and restoration of high-value dies/molds and aerospace components. The residual stresses developed in the material deposited via DLMD affect the structural integrity of the restored components. The service life of the restored component will be compromised if tensile residual stresses are present in the deposited layer. The residual stresses originate due to differential thermal expansion/contraction and martensitic transformation-driven volumetric dilation and transformation-induced plasticity. The influence of martensitic transformation and processing conditions on the residual stresses of DLMD-processed components needs to be understood and modeled for sustainable repair. Hence, a finite element model has been developed to capture the coupled effect of thermomechanics and martensitic transformation on the evolution of residual stresses in DLMD. In this study, the individual and coupled effects of strains due to volume dilation and transformation-induced plasticity on residual stress evolution have been analyzed for the deposition of crucible particle metallurgy (CPM) 9 V on H-13 tool steel. The finite element model has been experimentally validated using X-ray and neutron diffractions. The inclusion of both transformation strains in the residual stress decreases the prediction errors of peak tensile residual stress from ∼48% to ∼15%. The fully coupled thermomechanical and metallurgical model has been used to obtain a critical linear mass density (m˙/v) corresponding to the onset of a fully compressive longitudinal residual stress state in the deposited layer to ensure sustainable repair.

Residual stress in laser cladded heavy-haul rails investigated by neutron diffraction

Abstract Residual stress is one of the critical parameters affecting the fatigue behaviour of tribological components, which can be introduced by a thermo-mechanical process such as laser cladding. In this study, the residual stress distribution of laser cladded rails was evaluated using a neutron diffraction technique. The substrate rail for the laser cladding was hypereutectoid rail steel used in Australian heavy-haul railway track, and the cladding materials were 410L (a low carbon content stainless steel alloy) and Stellite 6 (a Co-based alloy). The cladding materials were selected based on their high wear, corrosion and fatigue resistance properties. This study measured the residual stress in full-scale laser cladded rails where the residual stresses were measured in the cladding layer, heat affected zone (HAZ) and substrate zone of the railhead. A new sample preparation strategy was developed to quantify the residual stresses in the full-scale rails with high spatial resolution. Higher compressive residual stress was found in the cladding layer, which may have resulted from the martensitic transformation occurred in that region. Tensile stresses occurred in the HAZ to a depth of 4 mm, which might be mainly caused by thermal contraction and volumetric change in the microstructure. The addition of a second cladding layer did not significantly affect the magnitude of the residual stresses, but the peak tensile residual stress shifted to a deeper location from the surface, which is beneficial in resisting wear. Post-cladding heat treatment significantly reduced the undesirable high residual stress from the cladding layer and HAZ.

Numerical analysis on the residual stress distribution and its influence factor analysis for Si3N4/42CrMo brazed joint

The residual stress distribution in Si3N4 ceramic-42CrMo steel joints brazed with TiNp-doped Ag–Cu–Ti composite filler has been investigated. The stress distribution in the specimens during cooling and four-point bending was simulated by finite element (FE) calculations using an elastic-plastic model. The FE simulation results indicate that the peak tensile axial residual stresses appear at the Si3N4 edge close to the interface. The experimentally determined joint strength based on the four-point bending test was compared with the results of the FE analysis, showing a reasonable agreement. The residual stress in the Si3N4-42CrMo joint decreases and then increases with the increase of TiNp content, resulting in an optimized joint strength. The consistency of the obtained results suggests that the stress distribution in the brazed joints can be reasonably predicted within the framework of this elastic-plastic FE model. Then the effect of the thickness of brazing layer and interfacial reaction layer on the stress distribution and joint strength was investigated. The FE results indicate that mechanical properties can be improved by increasing the brazing layer thickness and decreasing the thickness of the interfacial reaction layer. Nevertheless, to improve the experimental joint strength, we should carefully consider all critical properties of the joint rather than simply increasing the brazing seam thickness and decreasing the interfacial reaction layer thickness.

Alleviating surface tensile stress in e-beam treated tool steels by cryogenic treatment

Electron beam (e-beam) treatment of tool steel surfaces has been available for several decades as an approach to create hard surface layers on tool steels. The e-beam process produces ultrafine grain sizes through ultra-rapid cooling of the melt layer, which helps with improving wear resistance to increase the service life of tools. However, its implementation in many applications has been limited by the accompanying residual tensile stresses in the surface layer, which is undesirable and may lead to premature fracture. Here we report the utilization of cryogenic freezing after e-beam treatment to reduce the residual tensile stress. The e-beamed specimen contained high levels of retained austenite in the surface layer. The cryogenic treatment converted the retained austenite into martensite, and the corresponding volume expansion reduced the peak tensile residual stress by 28%, which makes it a promising method to expand the applications of e-beamed tool steel.

The effect of shoulder coupling on the residual stress and hardness distribution in AA7050 friction stir butt welds

The effect of shoulder coupling in friction stir welding (FSW) on the distribution of residual stresses, microstructure and hardness has been investigated by comparing welds manufactured with a conventional tool, using different levels of downforce, to joints produced using a stationary shoulder (SSFSW). The welds were produced in AA7050-T7651 6.35 mm plate with the same travel speed and similar power levels. Reducing the tool downforce in FSW led to a decrease in the overall shoulder input power, but a minimal reduction in the weld zone hardness and peak residual stresses. In contrast, relative to FSWs made with a similar input power, the stationary shoulder led to much more significant microstructure and property changes including a reduction in the HAZ width, an increase in the minimum weld zone hardness level and a significant reduction in the peak tensile residual stresses (by ~ 25%). With SSFSW, the improvement found in the hardness and residual stress distribution from eliminating the energy dissipated by the tool shoulder could be directly correlated to a reduction in the weld temperature and narrowing of the thermal field, which reduced the size of the HAZ and region of plastic misfit responsible for the weld residual stresses. By comparing the results with previous work it was found that, apart from using a stationary shoulder, the most important welding parameter affecting the weld zone peak tensile stresses was the travel speed, with longitudinal residual stresses doubling upon increasing the travel speed from 100 to 400 mm/min.

Comparison of residual stress distributions in conventional and stationary shoulder high-strength aluminum alloy friction stir welds

The residual stresses generated in stationary shoulder friction stir welds (SSFSWs) produced in a typical high strength aluminum alloy (AA7010) in 6.3mm thick plate has been mapped over full weld cross sections, using the contour method, and compared to those introduced by conventional friction stir welding (FSW) for welding speeds ranging from 100 to 400mm/min. Compared to in conventional FSW, as a consequence of the material flow being affected by only a rotating probe, the SSFSW process produced a narrower and more uniform weld nugget and heat affected zone profile through the plate thickness. For both processes, ‘M’ shaped residual stress distributions were determined. However, the peak stresses measured in the SSFSWs were slightly lower than those found in the conventional FSWs and the width of the tensile region was appreciably reduced when using a stationary shoulder welding tool. This is shown to be resulting from a more focused temperature distribution obtained from using only a rotating probe to generate heat in the SSFSW process. In both processes, increasing the welding speed led to a narrower residual stress profile, but higher peak tensile residual stresses.

Residual stresses in welded I-shaped sections fabricated from Q460GJ structural steel plates

A new type of high-performance structural steel named by GJ steel, has been widely used in many large scale structures like National Olympic Stadium (Birds Nest), new CCTV Headquarters and Canton Tower in China. However, previous studies on 460MPa GJ steel are very limited. In this study, the residual stresses on eight full scale I-shaped sections welded by flame-cut Q460GJ (“Q” means yield strength) steel plates including five doubly symmetric sections and three singly symmetric sections, were investigated by experimental tests. By using sectioning method, it was found that the deformation of curved strips was one part of circular curve. The results from the circular curve correction method are generally identical to the results from a new curve correction method named by “straightening measurement”. Then the residual stress distributions on Q460GJ welded I-shaped sections were obtained. It was concluded that residual stresses were related to sectional dimensions and flanges and webs were influenced with each other. Compared with the existing residual stress distribution models, the residual stresses on sectional flanges obtained in this study are much smaller, while no significant difference is found for sectional webs. It is also found that the flange tips are all under compression rather than tension, and the average value of the peak tensile residual stresses on flanges is only about 0.5fy. Finally, the residual stress levels at typical locations of I-shaped sections were summarized and suggested.

Finite element study of 3D simulated welding effect in aluminium plates

The effects of metal inert gas (MIG) welding and friction stir welding (FSW) on the development of the heat-affected zone (HAZ), residual stress and distortion fields in aluminium plates were investigated in this paper. The FSW and MIG butt welding process of two aluminium alloy 6061-T6 plates were simulated in a three-dimensional, two-step thermo-mechanical analysis using the finite element code ANSYS. The element birth and death technique was implemented in the MIG simulation to model the addition of weld metal to the workpiece and the tool plunging force and fixture release were considered in the FSW simulation. The finite element thermal results revealed that the FSW process resulted in significantly lower temperatures in comparison with MIG welding. The mechanical results indicated that in comparison with MIG welding, the FSW process resulted in up to 40% and 75% less peak tensile and compressive residual stresses, respectively, as well as a reduction of 40%– 60% in HAZ area and considerably smaller distortions.

Thermomechanical Analysis of Preheat Effect on Grade P91 Steel During GTA Welding

Effect of preheat on the thermal cycles, residual stress, and distortion during autogenous GTA welding of Grade P91 steel has been analyzed using FEM. Phase transformation effect on the residual stresses is also analyzed. Thermomechanical analysis has shown that preheat reduced the peak temperatures, cooling rate, and the distortion values. The phase transformation involving martensite during cooling resulted in typical “M” shaped residual stress profile with a reduction in peak tensile residual stress value and a wider distribution of residual stress. There is good agreement between the predicted and measured thermal cycles, residual stresses, and distortion of the P91 steel weld joint.

Effect of welding processes on the residual stress and distortion in type 316LN stainless steel weld joints

The effect of welding processes on the microstructure, residual stresses and distortion in 16mm thick 316LN stainless steel weld joints made by TIG and A-TIG (activated flux tungsten inert gas) welding processes involving different joint configurations have been studied. The joint configurations employed were double V-groove edge preparation for double side TIG welding, square-butt preparation for double side ATIG welding and Y groove preparation for weld joint made by both TIG and ATIG welding processes. All the weld joints passed radiographic examination. Microstructural characterization was carried out using optical microscope. Residual stresses were determined using ultrasonic technique employing LCR waves, and distortion measurements were carried out using height gauge. The three weld joints exhibited different microstructures, peak tensile residual stress values and distortion. The weld joint fabricated by double side A-TIG welding exhibited the lowest peak tensile residual stress value and also minimum distortion.

Simulation and Measurement of Through–Wall Residual Stresses in a Structural Weld Overlaid Pressurizer Nozzle

Full structural weld overlays (FSWOLs) have been used extensively as a repair/mitigation technique for primary water stress corrosion cracking in pressurizer nozzle dissimilar metal (DM) welds. To support an approved FSWOL design and safety submission for British Energy pressurized water reactor (PWR) nozzles, an in-depth evaluation was performed to assess the effects of a FSWOL on the through wall residual stress distribution in safety/relief pressurizer nozzles. Two safety/relief pressurizer nozzle mockups were fabricated based on British Energy’s PWR nozzle design. One mockup included the nozzle to safe-end DM weld and the safe-end to stainless steel weld, while the second mockup included the DM weld, the stainless steel weld, and a Westinghouse designed structural weld overlay. The mockups were fabricated utilizing materials and techniques that represented the plant specific nozzles as closely as possible and detailed welding parameters were recorded during fabrication. All welds were subsequently nondestructively evaluated (NDE). A thorough review of the detailed fabrication records and the NDE results was performed and several circumferential positions were selected on each mockup for subsequent residual stress measurement. The through wall residual stress profiles were experimentally measured through the DM weld centerline at the selected circumferential positions using both the deep-hole drilling (DHD) and incremental deep-hole drilling (iDHD) measurement techniques. In addition to experimental residual stress measurements, the through-wall residual stress profiles were simulated using a 2D axisymmetric ansys™ finite element (FE) model. The model utilized the application of temperature constraints on the weld elements to simulate the thermal welding cycle which greatly simplified the simulation as compared with detailed heat source modeling methods. Kinematic strain hardening was used for material modeling of the weld and base metals. A range of residual weld stress profiles was calculated by varying the time at which the temperature constraints were applied to the model. The simulation results were compared with the measurement results. It was found that the effects of the FSWOL were principally threefold. Specifically, the FSWOL causes a much deeper compressive stress field, i.e., the overlay shifts tension out toward the outside diameter (OD) surface. Furthermore, the FSWOL reduces tension in the underlying dissimilar metal weld, and finally, the FSWOL causes higher peak compressive and tensile residual stresses, both of which move deeper into the nozzle wall after the overlay is applied. Relatively good agreement was observed between the FE results and the measurements results.

Internal residual stress measurement on linear friction welding of titanium alloy plates with contour method

The internal residual stress within a TC17 titanium alloy joint welded by linear friction welding (LFW) was measured by the contour method, which is a relatively new and destructive technique to obtain a full map of internal residual stress. The specimen was first cut into two parts; the out-of-plane displacement contour formed by the release of the residual stress was then measured; finally, taking the measured contour of the cut plane as the boundary conditions, a linear elastic finite element analysis was carried out to calculate the corresponding distribution of residual stress normal to the cut plane. The internal stress distribution of the TC17 titanium alloy LFW joint was also analyzed. The results show that the tensile residual stress in the TC17 LFW weld is mainly present within a region about 12 mm from the weld centerline; the peak tensile residual stress occurs at the weld centerline and reaches 360 MPa (about one third of the yield strength of TC17 alloy); within the weld zone of the TC17 LFW weld, the through-thickness stress is not uniform, and the internal stress is larger than that near the top or bottom surface.

Residual stress distributions in welded stainless steel sections

Residual stress magnitudes and distributions in structural stainless steel built-up sections have been comprehensively investigated in this study. A total of 18 test specimens were fabricated from hot-rolled stainless steel plates by means of shielded metal arc welding (SMAW). Two grades of stainless steel were considered, namely the austenitic grade EN 1.4301 and the duplex grade EN 1.4462. Using the sectioning method, the test specimens were divided into strips. The residual stresses were then computed by multiplying the strains relieved during sectioning by the measured Young׳s moduli determined from tensile and compressive coupon tests. Residual stress distributions were obtained for 10 I-sections, four square hollow sections (SHS) and four rectangular hollow sections (RHS). Peak tensile residual stresses reached around 80% and 60% of the material 0.2% proof stress for grades EN 1.4301 and EN 1.4462, respectively. Based upon the test data, simplified predictive models for residual stress distributions in stainless steel built-up I-sections and box sections were developed. Following comparisons with other available residual stress test data, the applicability of the proposed models was also extended to other stainless steel alloys. The proposed residual stress patterns are suitable for inclusion in future analytical models and numerical simulations of stainless steel built-up sections.