Characteristics Of Residual Stress Distribution Research Articles

Exploring Weak Magnetic Signal Characteristics of Pipeline Welds: Insights into Stress Non-Uniformity Effects.

Weak magnetic detection technology can detect stress concentration areas in ferromagnetic materials. However, the stress non-uniform characteristics of pipeline welds lead to significant differences in stress distribution range and values between inner wall welds and outer wall welds. This discrepancy makes it crucial to further evaluate the impact of stress non-uniformity on magnetic signals. To study the magnetic signal characteristics under the influence of residual stress in weld seams, a magneto-mechanical analytical model was established based on the magnetic charge theory and the distribution characteristics of residual stress in the weld seam. The magneto-mechanical relationship and magnetic signal distribution characteristics at the inner and outer wall welds of the pipeline are calculated. Furthermore, the effects of different excitation intensities on the amplitude growth characteristics of magnetic signals are analyzed and compared. To verify the analysis model, weld detection experiments with different excitation intensities were designed. The results show that both the peak-to-valley values of the normal component and the peak values of the tangential component of the outer wall weld are lower than those of the inner wall weld. Conversely, the peak-to-valley width of the normal component and the peak width of the tangential component are greater than those of the inner wall weld. Additionally, the rate of increase in weak magnetic signal amplitude decreases in a first-order exponential relationship with increasing excitation intensity. The average decay rates of the normal and tangential component amplitude growth rates for the inner wall weld are 34.03% and 27.9%, respectively, while for the outer wall weld, they are 31.75% and 28.01%, respectively. This study contributes to the identification and quantitative assessment of weak magnetic signals in inner and outer wall welds.

Unraveling Residual Stress Distribution Characteristics of 6061-T6 Aluminum Alloy Induced by Laser Shock Peening.

Laser shock peening (LSP) is a powerful technique for improving the fatigue performance of metallic components by customizing compressive residual stresses in the desired near-surface regions. In this study, the residual stress distribution characteristics of 6061-T6 aluminum alloy induced by LSP were identified by the X-ray diffraction method, and their dependent factors (i.e., LSP coverage, LSP energy, and scanning path) were evaluated quantitatively by numerical simulations, exploring the formation mechanism of LSP residual stresses and the key role factor of the distribution characteristics. The results show that LSP is capable of creating anisotropic compressive residual stresses on the specimen surface without visible deformation. Compressive residual stresses are positively correlated with LSP coverage. The greater the coverage, the higher the residual stress, but the longer the scanning time required. Raising LSP energy contributes to compressive residual stresses, but excessive energy may lead to a reduction in the surface compressive residual stress. More importantly, the anisotropy of residual stresses was thoroughly explored, identifying the scanning path as the key to causing the anisotropy. The present work provides scientific guidance for efficiently tailoring LSP-induced compressive residual stresses to improve component fatigue life.

Determination of residual stress field in laser cladding using finite element updating method driven by contour deformation

Laser cladding is a cutting-edge technology widely used in additive manufacturing and surface modification. This process entails rapid melting and solidification driven by laser heating, which induces residual stress within the material. This study presents a data-driven approach to refine the numerical model of laser cladding, simultaneously emphasizing both the temperature characteristics and residual stress distribution within the thermomechanical coupling process. After integrating the residual stress distribution data obtained through the contour method with the molten pool morphology shaped by the thermal effects of laser cladding, a Levenberg-Marquardt optimization algorithm based finite element model updating scheme is proposed to efficiently identify the parameters of double ellipsoid heat source model, which employs parallel computing to reduce the computational time for iterations. The effectiveness of the proposed method is validated using experimental data. Moreover, this approach is adaptable, unaffected by the specimen size and shape, and can accurately predict the residual stress distribution characteristics. Therefore, it offers a robust framework for simulating the mechanisms of residual stress generation in titanium alloy laser cladding.

Experimental study on fatigue performance of double welded orthotropic steel bridge deck

Fatigue cracks which develop at multiple locations of orthotropic steel bridge decks (OSD) seriously deteriorate the safety and durability of steel bridges. U-rib fabricated using the double-sided penetration welding technique have been practically applied in bridges, but the fatigue performance of this type of U-rib has not been systematically studied. This study conducts fatigue tests on large-scale models of various fatigue details in the diaphragm area of orthotropic steel bridge decks with double-sided welds, obtaining the fatigue vulnerable locations and dominant cracking modes in the diaphragm area. The evolution law of out-of-plane deformation of diaphragm is clarified. The distribution characteristics of residual stress at the arched opening region and fatigue failure modes are acquired. Experimental results show that the interior weld toe of the U-rib-to-top-plate joint is the most fatigue-vulnerable zone, with a fatigue strength of 53.6 MPa. New fatigue cracks initiated from the weld toe of the top plate of the inner side of the U-rib or the weld toe of the U-rib perpendicularly or obliquely intersecting the longitudinal weld along 45° were found. After 10 million loading cycles, the residual stress in the arc-shaped opening area of the diaphragm reached 90–145 MPa, and the residual stress was higher where curvature of the opening was larger. The arc-shaped incision was in a circling state of tension and compression. It was also found that fatigue cracks that initiated from the weld toe of the diaphragm extended along the weld toe for some length before propagating into the diaphragm.

Study on modelling simulation and distribution characteristics of residual stress during robotic weld end grinding of high strength modulated steel

Welding technology is widely used in the aerospace, construction, machinery, and rail transportation industries. After the welding process is completed, the weld seam is typically ground to improve the assembly accuracy and surface integrity of the structural part. However, residual stresses on the surface after grinding often affect the product performance and service life of structural components. Therefore, the formation mechanism and distribution of residual stresses after the robotic weld end grinding of high–strength modulated steel welds were investigated. First, a local contact geometric model of the grinding wheel and weld was established, and a grinding -force contact model was built based on this model. Next, a model of the heat-flow distribution in robotic end grinding was analysed, and the magnitudes of the heat flow in the contact and weld-width directions were calculated for the contact area. The results of these calculations were similar to the actual heat-flow distribution. Then, based on a theoretical analysis, the finite element method was used with a birth–death element to establish a force-thermal coupled residual stress prediction model, which could simulate the material removal process during actual grinding. Finally, the accuracies and reliabilities of the theoretical and simulation models were experimentally verified. The maximum error between the maximum simulated temperature and experimentally measured value was 10 %. The minimum error was 3 % when using the same process parameters, and the residual stress error was approximately 15 %. Based on the simulations, the variations in the temperature and residual stresses with time and position were explored. The highest weld-contact surface temperature of 417.75 °C was found when grinding using process parameters ap = 0.2 mm, vs = 23.55 m/s, vw = 20 mm/s. The residual tensile stresses could be up to +553 MPa in the longitudinal direction and −161 MPa in the transverse direction. The temperature in the zone of demarcation between the weld and base material was 212.8 °C, with maximum residual tensile stresses in both the longitudinal and transverse directions, of up to 352 MPa. The analysis revealed that the magnitude of the residual stresses was consistent with the temperature variation pattern, and that the grinding depth had the greatest influence on the residual stress distribution.

Analytical model for thermo-mechanical interaction induced residual stress distribution during multi-conditional machining Inconel 718

Residual stress induced by coupling thermo-mechanical fields cannot be completely released and remains inside the workpiece after the cutting process, which has a significant impact on the fatigue resistance, corrosion resistance and deflection of manufacturing parts. This work focused on an analytical model for thermo-mechanical fields induced residual stress distribution during multi-conditional machining superalloy Inconel 718. Based on the relationships of material properties, cutting parameters, and cutting geometric conditions, the proposed analytical model investigated the thermo-mechanical fields based on the semi-infinite space elastic mechanical line load and the uneven film thermal stress distribution under the action of moving heat sources. The development process of residual stress was examined through the changes in the stress release process from loading to unloading based on the in-plane stress assumption solution. The effects of basic cutting variables including cutting speeds, uncut chip thickness and tool wear on the thermo-mechanical fields were discussed. According to the experimental and predicted results, the residual stress distribution characteristics were evaluated including surface residual stress, reverse peak stresses, transition position, and total influence depth, indicating that the proposed analytical model could obtain the residual stress distribution characteristics with the predicted error of approximately 4.3%–11.9%, 3.9%–73.4%, 4%–33.3%, and 3.3%–25.7%, respectively. This work can provide significant theoretical support for the analysis of the residual stress generation to control surface integrity during the cutting process.

Characteristics of residual stress distribution in wire-arc additive manufactured layers of low transformation temperature material

High heat input in wire and arc additive manufacturing (WAAM) tends to result in high tensile residual stress, which adversely affects performance and service reliability. However, low-transformation-temperature (LTT) materials are susceptible to compressive residual stresses due to their low phase-transformation point. Here, the LTT material 10Cr10Ni was used as the deposited material to fabricate a pipe structure, and the contour method was applied to measure the residual stress distribution in the cross-section. A thermomechanical coupling analysis model was developed to investigate the residual stress generation mechanism in 10Cr-10Ni(LTT) during the WAAM process. The simulated deformation and residual stress distributions agree well with the measurements. Through simulation analysis of the deposition of different layers, we found the key to the generation of compressive residual stresses in the LTT layers lies in whether there is a transformation from austenite to martensite during the final thermal cycle. When the deposition height exceeded 5.405 mm (approximately four layers), compressive residual stresses were only generated in the last four LTT layers and transformed into tensile residual stresses in the other layers. This results in a concept called the effective region, which can be used as a guide for reducing stress in WAAM using LTT materials.

Thermal-fluid-solid coupling analysis of vacuum brazing process for a titanium alloy plate-fin structure

Vacuum brazing is the most significant step in the production of titanium alloy plate-fin heat exchangers, and its quality regularly determines the mechanical properties and service life. In response to the demand, the thermal-fluid-solid coupling method was established, which focuses on the temperature uniformity, fluidity of brazing filler metal, residual stress distribution characteristics, and deformation distribution characteristics of titanium alloy plate-fin structure (PFS). The multi-field coupling mechanisms involved the vacuum brazing processes were investigated. The formation mechanism during the brazing process was parametrically analyzed using the developed model. The temperature distribution on PFS during vacuum brazing was non-uniform with a maximum temperature difference of less than 70 K. The velocity of fluid flow varied considerably across various regions of the brazing layer during vacuum brazing. The temperature gradient acted as the main driving force for fluid flow. Stress concentration was present at the upper surface of fins and in the middle of the backside. The PFS experienced significant deformation in the Z-axis, reaching a peak value of around 1.1 mm. By verifying experimental measurement results of deformation, the analysis approached based on the multi-field coupling was feasible and highly accurate.

Unique characteristics of residual stress distribution of large-diameter keyaki (Zelkova serrata) logs and examination of their measurement method

Large-diameter keyaki (Zelkova serrata Makino) logs have long been used in Japan as high-quality material especially for traditional construction and furniture. However, unlike other major wood species in Japan, keyaki has been practically considered as a wood species of high difficulty when processing. Keyaki frequently shows processing defects due to sawing, such as warping, cracking, and so forth, which often reduces the production yield of logs. Furthermore, there are drastic differences in those behaviors between individual logs, so causing unexpected processing defects. A scientific approach is required to improve this situation, but data on the material characteristics of keyaki were scarce. This study aimed to characterize the radial pattern of the residual stress as one of the processing-related characteristics. The measurement method was also examined. This study used diametral planks obtained from large-diameter keyaki logs to measure released strain of residual stress from pith to the bark sides. The results showed the distribution of released strain often showed peculiar zig-zag patterns characterized with localized residual stress, unlike the smooth bell curve pattern seen in typical logs of other species. Because of the unique characteristics, some practical points related to the measuring methodology were investigated. The extent of influence of this residual stress in the longitudinal direction was limited to within 30 cm from the site of measurement of the strain. In addition, the length of log necessary to measure the released strain without being affected by crosscutting was more than four times the log diameter—greater than the diameter ratio theorized by previous studies.

Analysis of residual stress distribution characteristics of laser surface hardening based on Voronoi model

The laser surface hardening’s parameters have a direct effect on the residual stress of the matrix. It is important to quantitatively reveal the influence degree of process parameters on the matrix residual stress for the formulation of optimal process. In this paper, a random polycrystalline model of the matrix is established based on the Voronoi method. The grain heterogeneity is introduced according to the nanoindentation results. The divided 7 different grain attributes are randomly assigned to each voronoi cell through a python script. A thermo-mechanical coupling model for the laser quenching process of SUS301L-HT stainless steel considering grain heterogeneity was established. The thermal stress field and temperature field distribution of the single laser surface hardening are calculated with different process parameters. On this basis, the BOX-Behnen Design method was used to establish a response surface model, and the response surface method was combined with the Monte Carlo sampling calculation method to calculate the sensitivity of the process parameters. The calculation results show that the analysis value D of the residual stress is a normally distributed. Laser power and laser scanning speed are the main factors affecting the average residual stress of the grain, and the effects of the two are opposite. The laser scanning speed has a greater influence on the residual stress of the matrix than the laser power.

Analysis of shot peening residual stress distribution based on dislocation configuration

The distribution profile of residual stress on the surface layer of shot-peened materials is often in a hook shape. We analysed the distribution characteristics of residual stress by detecting dislocation configurations. The position of maximum compressive residual stress (MCRS) shifts inward with an increase in shot peening strength. It was found that long-term orderly dislocation pile-up groups frequently appeared in the MCRS region. The location of MCRS is not necessarily related to maximum dislocation density. At low strength, both the maximum dislocation density and the MCRS are on the surface region. At high strength, the surface region structures are composed of sub-grains and dislocation cells. The position of maximum dislocation density is between the surface region and the MCRS.

Residual Stress Distribution Characteristics and Influencing Factors of 316L/Q235 Composite Plate during Heat Treatment

Residual Stress Distribution Characteristics and Influencing Factors of 316L/Q235 Composite Plate during Heat Treatment

Evaluation of Welding Residual Stress Characteristics of High-Strength Steel for Offshore Structures Based on Constraint Effect

The characteristics of welding residual stress distribution in high-strength steel for offshore structures were evaluated based on the effect of constraint. It is well known that high-strength steel exhibits a high welding residual stress, and the welding residual stress is a significant factor for evaluating unstable fractures. Test specimens were manufactured by applying different constraint conditions. The constrainted and unconstrainted specimens were welded with the same welding consumables and conditions to evaluate the welding residual stress distribution characteristics. The cutting method was applied to assess the welding residual stresses of both specimens. The results showed that the welding residual stress at the heat-affected zone of the unconstrainted specimen decreased compared with that of the constrainted specimen. However, angular distortion occurred in the unconstrainted specimen instead of reduced welding residual stress.

Characteristics of Welding Residual Stress Distribution in Dissimilar Weld Joints

For the construction of ecofriendly ships, fuels such as liquefied natural gas (LNG), ammonia, and hydrogen are being discussed as alternatives. LNG fuel has recently been applied to shipbuilding. The most important aspect of an LNG propulsion ship is the LNG storage tank, because LNG is stored at a high pressure and low temperature. Cryogenic steels are needed to evaluate safety in weld joints, especially the LNG storage tank which has a dissimilar weld joint with a STS pipe. The dissimilar weld joint has a complex welding residual stress distribution. It is necessary to evaluate the effects of temperature changes that occur during the loading–unloading process of LNG. In this study, the residual stress distribution characteristics of heterogeneous welding parts welded to STS pipes using 9% Ni steel, STS, and high-manganese austenitic steel in an LNG storage tank were investigated through experimental and analytical methods. The thermal stress due to the difference in thermal expansion coefficient between cryogenic steel and the STS pipe occurred with a small amount in loading–unloading of LNG. When high-manganese austenitic steels and the STS pipe were joined, tensile stress was generated at the dissimilar weld joint owing to the temperature difference generated during the LNG loading–unloading process. STS has a homogenous weld joint and identical thermal expansion coefficients; therefore, the shrinkage and expansion were not affected by the temperature change. The welding residual stress at the dissimilar weld joints was measured via an experimental cutting method, and the results indicated that the tensile residual stress had distribution similar to the yield stress of the material. The stress generated by the temperature change and the welding residual stress overlapped and occurred during the loading–unloading process of the LNG tank; however, the final tensile stress below the tensile stress was distributed in the storage tank.

Residual stress in wire and arc additively manufactured aluminum components

In this study, a number of numerical simulations have been performed to analyze the distribution characteristics of residual stress (RS) in the wire and arc additive manufacturing (WAAM) components made of aluminum alloys. Experiments have been performed to measure temperature results (thermal cycles, etc.), residual stresses, and deformation for verification. The results show that the variation in the height of beam can affect the magnitude and distribution of longitudinal RS in both the substrate and the beam, while that can only influence the transverse RS in the substrate but not in the beam nearly. The longitudinal RS on the top surface of the last layer in the WAAM parts changes from tension to compression if the height of beam is above a certain value (about 20 mm here), which is obviously different from that in the multi-pass weldments and the selective laser melting (SLM) components. The restraint condition of the substrate can apparently affect the magnitude and distribution of longitudinal RS in the beam, while that almost has no influence on transverse RS in the beam. In terms of numerical results, the generation mechanism and distribution of RS in WAAM components have been systematically illuminated in the current work, which is quite useful to guide the mitigation of the generated high RS.

Finite element analysis of stress and distortion for welding reinforced structure of angular steel used for power tower under load

Based on thermal-elastic-plastic theory, a three-dimensional numerical model of residual stress and distortion in L-shaped welding reinforced structure of angle steel used for power transmission tower is developed. The characteristics of residual stress distribution and deformation are numerically investigated, which are compared with the stress and deformation under the action of lateral compressive load. The research results show that, a large stress is generated in and near the weld zone. With enhancing the weld bead length, both equivalent stress and residual distortion have a growth, and the equivalent stress peak reaches 329Mpa, slightly lower than the yield stress of base metal, meanwhile the longitudinal residual stress peak is 399Mpa, higher than the yield stress of base metal. Under the action of 15000Pa lateral compressive load, the stress has no obvious change in the near weld zone of reinforce structure compared with that without load, and the distortion peak reaches 11mm.

Residual Stress Relaxation of DRWDs in OSDs under Constant/Variable Amplitude Cyclic Loading

An orthotropic steel deck (OSD) has a complicated structure, and its fatigue life is mainly determined by various welding details. Fatigue assessment of deck-to-rib welding details (DRWDs) under long-term train loads is an important concern for engineers. Properly assessing the initial residual stress and the mechanism of stress relaxation in DRWDs under long-term external loading is a prerequisite for predicting the fatigue damage and service life of OSDs. In this paper, a finite element analysis method is proposed to calculate the residual stress relaxation in DRWDs of OSDs under constant/variable amplitude cyclic loading. First, experiments on full-size OSD specimens were carried out using the hole drilling strain-gauge method, and the multi-axial distribution characteristics of residual stress on the sub-surface of the deck were obtained. On this basis, a refined residual stress analysis model of DRWDs using thermal-structural sequence coupling analysis and life and death unit technology is established, and the accuracy of the model is verified by the test data. Second, a coupling stress analysis model that considers the welding residual stress and mechanical stress using cyclic plastic constitutive model is established. The combined influence of number of cycles, stress amplitude, and stress ratio on multi-axial residual stress relaxation effect under constant/variable amplitude cyclic loading is investigated. Finally, a release formula of welding residual stress relaxation coefficient is proposed based on the external loading stress amplitude, stress ratio, and material yield stress. The results show that (1) with the increase in the number of loading cycles, the stress decreases until it is stabilized, while the global distribution of welding residual stress remains unchanged. Most of the welding residual stress release (about 95%) occurs in the first cycle; (2) the residual stress relaxation decreases with the increase in stress amplitude and increases linearly with the stress ratio; (3) the residual stress release is controlled by the maximum amplitude stress in the variable amplitude cyclic loading. After the residual stress is released, the stress will not continue to be released if the DRWDs have the same or smaller amplitude loading.

Prediction of residual stress with multi-physics model for orthogonal cutting Ti-6Al-4V under various tool wear morphologies

• The multi-physics modeling was proposed to analyze the residual stress distribution. • The additional stresses due to tool wear morphologies were integrated. • The relationship between residual stress index and tool wear was developed. The machining-induced residual stress has a pivotal impact on the corrosion resistance, fatigue, and functionality of manufactured components. Tool wear process induces the tool geometrical alterations, thereby affects the thermo-mechanical loads and residual stress distribution in the manufactured components. This work proposed a multi-physics model with the considerations of wear induced tool geometrical alterations to predict the residual stresses distribution for orthogonal turning Ti-6Al-4 V. These tool geometrical alterations included the flank wear, cutting edge radius, and rake angle. The proposed model framework involved five steps: (i) cutting force, (ii) temperature distribution, (iii) mechanical stress, (iv) thermal stress, and (v) calculation residual stresses by relaxation procedure. The experimental results verified that this model could effectively evaluate the residual stress distribution characteristics under tool wear conditions. Based on the prediction results, the response relationship analysis between the residual stresses and tool wear conditions was developed. This work could provide a novel method to control the residual stress distribution through monitoring of the tool wear morphology.

Numerical analysis for stress fields induced by laser trepanning of square-slotted blind holes with and without ultrasonic assistance

The numerical simulation on laser trepanning of square-slotted hole and hole array in stainless steel sheets with and without ultrasonic assistance was reported for analyzing the stress fields on the workpieces trepanned. Based on reasonable modification and verification for the established models using corresponding experimental results, the transient and/or residual stress distribution characteristics, which were induced by single hole trepanning and hole array trepanning with and without ultrasonic assistance, were analyzed systematically and numerically using finite element method (FEM) coupled with self-developed subprograms after predicting the transient temperature fields. The influence of ultrasonic assistance on stress reduction was also discussed. It was shown that the distribution characteristics of equivalent von-Mises stress fields on the top surface of laser trepanned workpiece were different from those on its corresponding bottom surface. For laser-trepanned workpieces, the residual stress distribution characteristics predicted after sufficient cooling were different from the corresponding transient stress characteristics simulated without sufficient cooling. As a whole, the ultrasonic assistance resulted in a small change for the distribution trend of the transient/residual stress field predicted, while the influence of ultrasonic-induced softening effect on laser trepanned workpiece was primarily demonstrated by the effective reduction of the stress values.

The shot peen forming of fiber metal laminates based on the aluminum-lithium alloy: Deformation characteristics

The deformation behavior of novel fiber metal laminates based on aluminum-lithium alloy (NFMLs) after shot peen forming was investigated to further reveal their deformation mechanism and seek a desired forming method. AZB425 ceramic balls were used to sharp the NFMLs strips with various shot peening intensity and coverage. Furthermore, arc height of the laminates was measured to describe the deformation behavior. The X-ray and layer removal methods were adopted to reveal the distribution characteristics of residual stress. The results indicated that the forming curvature of 165.24 mm was achieved for 3/2 cross-ply NFMLs. Plastic deformation was produced only in the shot peened metal layer, while elastic deformation in other fiber and metal layers. Comparing with metal materials, NFMLs possessed similar deformation rules following the variation of shot peening intensity and coverage. However, the laminates were inclined to deform perpendicular to fiber direction. Besides, shot peening significantly changed the residual stress state of NFMLs. The distribution of residual stress for shot peened NFMLs was obtained qualitatively in this study. The relaxation behavior of complicated residual stress was negligible even after 1000 times thermal impact from 100 °C to 0 °C.