Residual Stress Distribution Research Articles

Improvement of Fatigue Characteristics of Friction Stir Welded A6061-T6 Applying Shot Peening

Recently, researchers have developed the method as a harmless the crack by the surface modification. For the purpose of contributing to reliability improvement of the A6061-T6 structure by harmless method, the following research was carried out: The tensile residual stress of friction stir welding was added by shot peening, resulting in a more significant compressive residual stress than that of the base metal. The effect of the surface crack aspect ratio on the maximum harmless crack depth (ahml) of A6061-T6 was evaluated for residual stress distribution. The detectable depth was evaluated in the relationship between ahml and the maximum detectable crack depth (aNDI) by non-destructive inspection (NDI).

Exploring Through-Thickness Residual Stress Distribution in Double V-Groove Multipass Welds of High-Strength Low-Alloy Steel and the Impact of Mechanical Restraints

Exploring Through-Thickness Residual Stress Distribution in Double V-Groove Multipass Welds of High-Strength Low-Alloy Steel and the Impact of Mechanical Restraints

Exploring residual stress analysis in the machining of hypoeutectic high chromium white cast iron alloys through the hole-drilling method

Abstract High chromium white cast irons (HCWCIs), ASTM A352, Type A and Class III, i.e., 25%Cr iron in as-cast condition consists of proeutectic austenite (γ-Fe), transformed martensite (α-Fe) and discontinuous Cr-rich, i.e., M7C3/ (Cr, Fe)7C3 type of carbides, which are hard and brittle in nature. Fully annealed thermal treatment was performed to improve iron’s machinability leading to fully pearlitic matrix with minor retained γ-Fe content. Eutectic (Cr, Fe)7C3 type of carbides are not affected by heat treatment processes. Resulting from corresponding manufacturing process, the magnitude and distribution of residual stresses (RSs) in as-cast and after machining were measured using hole-drilling method (HDM), as they are known to be harmful to corrosion and fatigue resistance. Furthermore, general metallurgical material characterisation was performed in as-cast and heat-treated conditions. As a result, this study revealed hardness variation, 547 and 555BHN in as-cast as compared to 327BHN in heat-treated condition. Furnace and actual cast component chemical analysis revealed a slight variation, especially between carbon (C) and chromium (Cr). Furthermore, eutectic type of carbides and precipitated secondary, i.e., (Cr, Fe)23C6 type of carbides within fully pearlitic matrix with minor amounts of retained γ-Fe were detected within the dominant matrix, i.e., pearlitic matrix in as-annealed condition. Detected magnitude and distributions of RSs on heat-treated sample resulted in higher tensile stresses in the surface and compressive in the interior as compared to sample in as-cast condition. Thus, this study was successfully in measuring RSs in as-cast and upon machining of hypoeutectic irons of HCWCI alloys using HDM.

Simulation and experimental investigation of grain structure, residual stress,γ′ phases in single crystal blade

Ni-based superalloy turbine blades have been required components in contemporary aero-engine. Knowing the solidification behavior, residual stress at grain defects, and microstructure of directionally solidified turbine blades is a required condition to improve the service performance of directionally solidified turbine blades. Firstly, the temperature field evolution of the blade under the withdrawal rate of 3 mm/min was studied. The deviations in temperature distribution in the high-rate solidification (HRS) procedure, particularly near the platform, can lead to transformations in the mushy zone, potentially resulting in solidification defects. Secondly, the grain growth of hollow turbine blades was calculated using the cellular automaton-finite factor method. The simulated grain framework was essentially consistent with experimental results. A method of process bar addition based on physical field distribution is also proposed. This method involves designing a combination of one Y-shaped and two I-shaped rods to decrease the cooling rate of blade edges and eliminate stray grains (SG). Then, the residual stress distribution at the locations of stray grains and low-angle grain boundaries (LAGBs) was analyzed before and after the addition of process bars. Finally, discussions were held regarding the distribution of γ′ phases in grain defects and blades.

Study on the effect of variable laser power on residual stress distribution in laser directed energy deposition of Ti6Al4V

In the laser directed energy deposition (LDED) process, cyclic thermal stress loading induces significant temperature variations on the surface and subsurface of the workpiece during repeated heating, leading to the formation of residual tensile stress during cooling. This adversely affects the mechanical properties of the parts, causing deformation and defects. In this study, a heat transfer model and a three-dimensional stress model were established based on finite element analysis. A variable laser power (VLP) deposition strategy was proposed to dynamically simulate the temperature and stress fields of Ti6Al4V titanium alloy under different deposition strategies. The model was validated by collecting substrate temperature variations using thermocouples and measuring residual stress with an X-ray diffractometer (XRD). Experimental results showed that the temperature error between the simulation and the experiment ranged from 6.25 % to 10.12 %, with an average stress simulation error of 6.92 %. Among the four strategies, the samples using the VLP strategy showed a reduction in the average substrate temperature by 12.68 % to 15.08 % compared to the other three strategies. The maximum principal stress in the layer was reduced by 7.8 % to 32.14 %, and the residual stress distribution was more uniform in all directions. The microstructure of the deposition layer further indicated that the VLP strategy improves residual stress distribution and leading to better deposition quality.

Residual stress prediction in Ti17 linear friction welds considering inhomogeneous mechanical properties of joints

Microstructural variations of joints occur in linear friction welding, resulting in inhomogeneous mechanical properties that affect the development of residual stress. The mathematical models for elastic moduli and yield strength of Ti17 were firstly developed to obtain the inhomogeneous mechanical properties of joints. Then, the influence of inhomogeneous mechanical properties on residual stress prediction was investigated. The results show that the finite element model considering inhomogeneous mechanical properties accurately captures the bimodal distribution of residual stress and the location of peak stress in joints. Numerically, the peak values of stress are ∼662 and ∼194 MPa along the direction of oscillation and forging, respectively, which is consistent with the result of the contour method.

Effect of Dual Shot Peening on Microstructure and Wear Performance of CNT/Al-Cu-Mg Composites.

This work systematically investigated the effect of dual shot peening (DSP) and conventional shot peening (CSP) on the microstructure, residual stress and wear performance of the CNT/Al-Cu-Mg composites. The results indicated that compared with CSP, DSP effectively reduced surface roughness (Rz) from 31.30 to 12.04 μm. In parallel, DSP introduced a smaller domain size (33.1 nm) and more dislocations, higher levels compressive residual stress and a stiffer deformation layer with deeper affected zones. Moreover, DSP effectively improved the uniformity of the surface layer's microstructure and residual stress distribution. The improvement is mainly due to secondary impact deformation by microshots and fine grain strengthening. In addition, the transformation of the hard second phases such as Al4C3 and CNT and its effects on improving the surface strength and deformation uniformity were discussed. Significantly, DSP improved the wear resistance by 31.8% under the load of 6 N, which is attributed to the synergistic influence of factors including hardness, compressive residual stress, surface roughness, and grain size. In summary, it can be concluded that DSP is an effective strategy to promote the surface layer characteristics for CNT/Al-Cu-Mg composites.

Mechanisms of laser non-uniform shock peening on the mechanical properties of SUS 304 stainless steel weld joints

The technique of Laser Non-Uniform Shock Peening (LNUSP) is proposed based on the residual stress distribution in welded joints and the shock wave peak pressure of SUS 304 stainless steel. The study investigated the effects of LNUSP on the mechanical properties of laser beam oscillation welded (LWW) joints of SUS 304 stainless steel. The results indicate that LNUSP induced residual compressive stress with an affected layer depth exceeding 0.9 mm, leading to a more uniform residual stress distribution. LNUSP also induced martensitic phase transformation, altered the grain structure orientation, formed parallel dislocation arrays that refined the grains, increased dislocation density leading to dislocation tangles, and induced mechanical twins of 20–70 nm. Furthermore, LNUSP significantly enhanced microhardness and promoted a more uniform hardness distribution, favoring a better balance between strength and ductility. LNUSP notably increased the yield strength (YS) and ultimate tensile strength (UTS) by 49.4% and 5.1%, respectively, compared to the original samples. The LNUSP-treated samples demonstrated superior strength and plasticity, attributed to the uniformity of internal plastic deformation.

FEM Investigation of the Roughness and Residual Stress of Diamond Burnished Surface

Characterization of surface integrity is possible with three critical metrics: microstructure, surface roughness, and residual stress. The latter two are discussed in this paper for low-alloyed aluminum material quality. Ball burnishing is a regularly used finishing procedure to improve surface roughness, shape accuracy, and fatigue life, taking advantage of the fact that it can favorably influence the variation in stress conditions in the material. The effect of burnishing is investigated using finite element simulation with DEFORM 2D software using the real surface roughness of the workpiece. The FEM model of the process is validated with experimental tests, the surface roughness is measured using an AltiSurf520 measuring device, and the residual stress is analyzed with a Stresstech Xstress 3000 G3R X-ray diffraction system (Stresstech, Vaajakoski, Finland). The results indicate that the burnishing process improves the surface roughness and stress conditions of AlCu6BiPb low-alloyed aluminum, and the study shows that there is good agreement between the FE and experimental results, further revealing the effect of the process parameters on the distribution of the compressive residual stress.

A comparative analysis of the impact of fillet weld geometry on residual stress distribution in nickel-based superalloy

A comparative analysis of the impact of fillet weld geometry on residual stress distribution in nickel-based superalloy

Microstructure and residual stress gradient evolution mechanism of electronic copper strip for lead frame

The miniaturization of integrated circuits has led to a shift in lead frame fabrication methods from physical stamping to chemical etching. However, this process is highly sensitive to residual stress. We investigated the gradient distribution of residual stress, microstructure, and macroscopic texture in electronic copper foils using a layer-by-layer peeling method, and proposed a novel strategy for evaluating residual stress levels. Our findings reveal that the rolling-induced residual stress exhibits a gradient distribution along the thickness direction. Specifically, from the surface to the central layer, the stress transitions gradually from tensile to compressive, with the stress type primarily influenced by metal flow during rolling. Additionally, we observed gradient variations in the S and Cube texture. Tensile stress favors the formation of Cube-texture, while compressive stress promotes S-texture development. Notably, Cube-texture can lead to strain localization during rolling, directly impacting the local residual stress levels and distribution. Furthermore, quantitative analysis of dislocation density using peak profile methods revealed a consistent trend between {111} plane dislocation density and lateral residual stress. Further investigation highlighted that dislocations and precipitates associated with {111} planes in face-centered cubic metals significantly influence residual stress, with their combined effects determining the overall stress magnitude in relation to texture, dislocations, and precipitates.

Three-dimensional polarimetric ptychography

A three-dimensional polarimetric ptychography (3D-PP) technique is proposed to reconstruct the residual stress distribution in optical elements in three dimensions by combining polarization imaging and a 3D ptychographic iterative engine (3D-PIE). 3D-PP mainly uses two orthogonal linear polarizers placed along the light direction to capture the photoelastic information within an optical element. Based on phase shift theory, a three-step phase shift method is proposed to record three dark field images, allowing for calculating the isometric line of residual stress within the optical element. This method enables the layer-by-layer measurement of residual stress within thick samples and assesses the distribution of residual stress along the detection axis, enhancing the precision of stress measurements.

Simulation study of turning-ultrasonic rolling compound processing for 42CrMo steel

The ultrasonic rolling processing technology has been shown to significantly reduce surface roughness and enhance the residual stress of parts, thereby improving their surface properties and extending their service life. This technology is particularly effective for the precision machining and surface strengthening of ultra-high-strength steel 42CrMo. This study aims to investigate the impact of turning pre-processing on the distribution of residual stress during ultrasonic rolling, a simulation model incorporating turning pre-processing was developed and used to conduct ultrasonic rolling simulation experiments, enabling the analysis of residual stress distribution patterns. Concurrently, ultrasonic rolling strengthening experiments were performed to validate the accuracy of the simulation model. The results confirm that with increasing rotational speed and feed rate, residual stress decreases, whereas with increasing static pressure and amplitude, residual stress increases. The residual stress variation obtained from the simulation of combined turning and ultrasonic rolling closely matched the results of experimental ultrasonic rolling tests. This consistency validates the accuracy of the simulation model. This study offers a novel approach for simulating and experimentally validating ultrasonic rolling processes, particularly for shaft-like parts that undergo turning as a pre-processing step.

Investigating temperature, stress, and residual stresses in laser powder bed fusion additive manufacturing of Inconel 625

Laser powder bed fusion (LPBF) is a pivotal method in metal additive manufacturing, enabling the intricate fabrication of complex components. However, the rapid thermal transitions inherent in LPBF can induce residual stresses, potentially leading to defects like distortions, cracks, and delamination. This research aims to investigate the distribution of temperature and stress during the LPBF manufacturing of Inconel 625, as well as the generation of residual stresses. For this purpose, a three-dimensional finite element (FE) model of the LPBF process was developed to explore the influence of various factors, including the number of layers, deposition region dimensions, and layer thicknesses, on temperature and stress distribution. Additionally, the study thoroughly examined the residual stress occurred on the part related to post-cooling and their variations after substrate separation. The outcomes reveal that the dimension of the deposition region significantly impacts both temperature and the size of the melt pool. The melt pool depth of 91 μm was calculated from the FE models, closely aligning with the experimentally measured value of 84.7 μm. Furthermore, the separation of the substrate has a notable effect on the distribution of residual stresses in the LPBF specimen. For instance, the residual stress at the center of the first layer decreased from 818 MPa after the cooling process to 108 MPa following substrate separation.

Study of Residual Stress Using Phased Array Ultrasonics in Ti-6AL-4V Wire-Arc Additively Manufactured Components

This paper presents a study on residual stress measurement in wire-arc additively manufactured (WAAM) titanium samples using the non-destructive method of phased array ultrasonics. The contour method (CM) was used for the verification of the phased array ultrasonic results. This allowed for a comparison of measurement methods to understand the effects on the distribution of residual stress (RS) within Ti-6Al-4V samples and the effectiveness of measurement of residual stress using phased array ultrasonics. From the results of the experiments, the phased array ultrasonic data were found to be in good agreement with the CM results and displayed similar residual stress distributions in the samples. The results of the individual elements of the phased array were also compared and an improvement in accuracy was found. From per-element results, anomalies were found and could be mitigated with the ability to average the results by using phased array ultrasonics. Therefore, based on these results, there is a strong case for the benefits of using phased array ultrasonics as a method of residual stress measurement for WAAM Ti-6Al-4V components over other existing residual stress measurement techniques.

Analysis of variables in finite element analysis for multi-pass welding in nuclear power plant components, part 1: Comprehensive study with experimental validation using scientific weld specimen

The influence of various parameters in welding simulations using finite element analysis (FEA) was investigated in this study. Welding experiments and finite element simulations were conducted to analyze residual stress and post-welding distortion. It was a specially designed V-groove specimen, filled with bead passes using Gas Tungsten Arc Welding (GTAW), that facilitated the measurement of distorted shapes and residual stress. Advanced measurement techniques, including three-dimensional laser scanning and the contour method, were used to capture detailed data on the welded specimen. Three different heat source models (body heat flux, temperature boundary, and Goldak's double-ellipsoidal model) were employed in the simulations, and their effect on residual stress distributions was analyzed. Additionally, the effects of hardening models, bead deposition methods, bead shape modeling, welding sequences, and lumping of weld passes on simulation were systematically analyzed. The findings suggest that a combined approach using different modeling techniques and careful calibration of parameters can enhance the reliability of simulations in predicting weld residual stress and distortions.

A novel model for predicting deformation of thermoplastic composites during heat-pressing process

Carbon fiber/polyetheretherketone (CF/PEEK) thermoplastic composites are widely used in the aerospace industry due to their excellent mechanical properties and high-temperature resistance. However, the research on heat-pressing deformation and residual stress during high-temperature and high-pressure heat-pressing processes in CF/PEEK was relatively deficient. In this paper, a framework coupled with crystallization kinetics, micromechanics and thermodynamics was developed to predict the heat-pressing deformations of CF/PEEK and it was conducted by UMAT, DISP and UEXPAN subroutines. Moreover, the predictive model was verified by experiments effectively. Finally, we compared the difference in residual stress distributions between symmetric and asymmetric lay-ups and found that the melting temperature, thickness, angle and sequence of layers have a significant impact on the heat-pressing deformation. This work provided an effective tool for predicting heat-pressing deformations, which is great of significance in the manufacturing and application of CF/PEEK.

The effect of productive and quality deposition strategies on residual stress for Directed Energy Deposition (DED) process

In the Directed Energy Deposition (DED) realm, challenges persist concerning process stability and mechanical properties in as-built components. Facts like inconsistent laser head feed rate and accumulated heat during multi-layer deposition result in variations in melt pool energy, causing variant clad widths and heights. Moreover, significant residual stress in as-built DED parts can induce excessive distortions and cracking. To tackle these challenges, offline energy control systems that adjust laser power or feed rate have been implemented to manage melt pool energy and improve productivity. Additionally, an innovative online clad height compensation system has been developed to achieve global height geometry, further boosting productivity. However, the impact of these productive and quality control systems on the mechanical properties of austenitic stainless-steel parts, specifically residual stress, remains unexplored. In this research, residual stress measurements in as-built DED thin wall parts fabricated with energy and/or height control strategies using neutron diffraction have been investigated. The control of three key DED parameters influencing residual stress distribution and magnitude has been identified and discussed. Measurements indicate that neither offline energy control nor online height control adversely affects the quality of the thin wall parts and offline LP-based energy control can reduce residual stress magnitude and its variation. Additionally, the height control results in compressive residual stress with elevated magnitudes. Furthermore, aggressive DED parameters hold the potential for further improvement by pairing with an energy control strategy. This study establishes a foundation for further developing comprehensive control strategies designed to enhance the productivity and quality of DED systems.

Improving the surface durability of wind gears via shot peening and superfinishing

Gearbox power density plays a key role in wind energy competitiveness. As wind turbines have become increasingly larger, gear surface durability and flank fracture load carrying capacity have become key elements in gearbox sizing. While shot peening and superfinishing have been studied independently as potential techniques to improve surface durability, few reported studies have combined both of these processes to increase the gear flank load-carrying capacity. In this work, spot pitting tests were carried out to evaluate the expected load-carrying capacity increase for wind gears through this combination of finishing processes. The results are consistent with previous research's conclusions and highlight the need for further investigations to evaluate potential increased flank fracture risk related to the near-surface residual stress distribution.

Nanoscale stress and microstructure gradients across a buckled Mo-Cu bilayer: Cu self-annealing triggered by interface delamination

Residual stresses in thin film structures significantly impact their mechanical properties and affect interface delamination. Highly compressively stressed thin films buckling is the predominant interfacial failure mode due to strain energy release. In the present study the effect of cross-sectional stress and microstructural gradients of thin films on the buckling behavior are explored in a model material system consisting of a thin Cu film sputtered onto glass and a highly compressively stressed 500 nm thick Mo overlayer causing buckling delamination at the Cu-glass interface. Employing synchrotron cross-sectional X-ray nano-diffraction, multiaxial X-ray elastic strain and microstructure distributions were explored across the cross-section of the adhering and buckled bilayer, respectively. In the adhering state, a gradual thickness evolution of columnar microstructure and residual stress was found for Mo, while in Cu, no microstructure changes and only minimal stress variations were detected along the film thickness. After delamination, diffraction peak broadening and changes in unstrained lattice parameters in the Cu sublayer indicated structural defect annihilation and grain coarsening. These microstructural changes were further validated via cross-sectional transmission electron microscopy. The evaluated residual stress distributions across the two sublayers of the pristine and buckled bilayer were used to quantify the released strain energy per unit area due to buckling, amounting to 0.61 J/m². Further cross-validation of experimental stress results with finite element simulations strengthened the experimental findings, providing a comprehensive understanding of the stress distribution across the buckled bilayer.