Residual Stress Profiles Research Articles

Microstructural and Residuals Stress Analysis of Friction Stir Welding of X80 Pipeline Steel Plates Using Magnetic Barkhausen Noise

Friction stir welding is a solid-state joining method conducted under large stress and strain conditions at low peak temperatures when compared to arc welding. Friction stir welding produces a large variety of microstructures and a M-shaped residual stress line profile along the cross-section of the welds. In this work, we present the use of magnetic Barkhausen noise to qualitatively assess the residual stress profile along the transverse direction of a two-pass friction stir welding butt joint on a X80 pipeline steel. Results were compared and correlated to X-ray diffraction, microstructural and hardness characterization. The peak position and the root mean square profiles of the magnetic Barkhausen noise reproduced the residual stress profile obtained by X-ray diffraction and the hardness profile, respectively. These results can be used for developing a qualitative quality control method for friction stir welding joints in other steels.

Influence of base material, tempered condition and hardening pattern on the residual stress profile of induction hardened gears

This paper discusses influences of the base material, pre-heat treatment and hardening pattern on the residual stresses of induction hardened gears with module 2 and 4 mm. The gears were hardened in a simultaneous dual frequency induction hardening process. After the hardening process, no peening was applied. Depending on the hardening pattern, base material and tempered condition, a wide range of residual stress profiles did occur, with the surface residual stresses reaching from compressive to tensile residual stresses at the tooth flank depending on the variant. In this paper, the main influence parameters on the residual stress profile will be identified.

Parametric Study of Fixtured Vibropeening

Vibropeening is a surface treatment process, which combines the peening effect of introducing residual stress with the polishing effect of reducing surface roughness in one single process step. Vibropeening equipment induces vibrations into the media to impart residual compressive stresses in sub-surface layers, as well as polishing on the surface of the work piece. In addition to process parameters, such as vibration frequency, amplitude, and media mass, which are well known in literature, this paper will focus on the study of two additional parameters: immersion depth and process time. It was found that the lower-middle section of the vibratory trough produced the highest Almen deflection. Different continuous treatment times were also studied to explore the maximum introducible residual compressive stress state, and it was concluded that an optimal time range is required to achieve the best residual stress profile. The study demonstrates that different process parameters can influence the effectiveness of the vibropeening process, and that these can be potentially optimized for higher treatment capability.

Experimental and numerical study of pneumatic needle peening effects on Aluminium Alloy 2024-T3

Pneumatic needle peening process was experimentally calibrated using high speed camera and numerically simulated using previous developed shot peening and peen forming finite element (FE) models. High speed photography was applied to record the images of peening needles and digital image treatment program was developed to calculate needle peening velocities for the FE simulation. A single impact simulation was performed for convergence study and indentation comparison to validate the impact model. Good accordance between the simulated and experimental indentation diameters was obtained. Then multiple needle impact models were applied to simulate the induced stress profiles for different peening conditions. Finally, the induced stress profiles were input into a peen forming FE model to predict the specimen deflections (or arc heights). Similar to Almen intensity definition, saturation point was determined by defining certain peening time, when double peening time, the produced arc height increases equal to 10%. The residual stress profile at saturation time for one of the scenarios was calculated and compared against the X-ray diffraction (XRD) measured results at the same operating pressure. In addition, the residual stress profile calculated from the induced stress profile using analytical equations was compared with XRD measurements. Compared to experimental measurements, both the model simulated and analytical calculated residual stress profiles were able to predict the surface compressive residual stress and maximum compressive residual stress very well. The simulated deflection results for the studied peening pressures were then compared against the deflection measurements using the coordinate measuring machine (CMM). The difference between experimental and predicted results ranges between 0.3% and 13.2% for the four higher peening pressures. However, for the lowest peening pressure, larger error of 50% was obtained, which can be explained as the overestimation of the peening velocity at the lowest peening pressure. In conclusion, the presented methodologies are able to calibrate the peening velocities, to predict the induced stresses and further to calculate sample deflections of thin specimen by pneumatic needle peening.

Surface Modification of a Cold Gas Dynamic Spray-Deposited Titanium Coating on Aluminum Alloy by using Friction-Stir Processing

In this research, the parameters of the cold spray process were initially assessed for deposition of a pure titanium coating layer with the thickness in the range of 800-850 µm on an AA5083 alloy substrate. Thereafter, to enhance the structural integrity of Ti-coating layer and decrease the coating porosity, friction-stir processing was employed as a post-modification technique by using a flat cylindrical tungsten carbide tool. The plunge depth of the friction-stir tool (in the range of 0.3-0.5 mm) was found to significantly affect the densification of the porous titanium coating layer. Optical microscopy, field emission-scanning electron microscopy, electron backscattering diffraction, transmission electron microscopy analysis and indentation Vickers micro-hardness testing were conducted on the thickness cross-sections of cold-sprayed coatings to characterize the microstructural features and mechanical properties before and after friction-stir modification performed using two different plunge depths. Furthermore, residual stress profiles on the surface were determined by using x-ray diffraction analysis technique. Significant grain refinement, from an initial cold-sprayed coating grain size of less than 25 µm to grain sizes < 1 µm, was observed across the thickness section of modified samples with a gradient profile from the coating surface toward the interface depending on the plunge depth. After friction-stir processing, the hardness of a thin layer close to the surface of coating increased up to seven times higher as compared to the cold-sprayed material.

Fatigue strength prediction methodology of shot-peened materials

Shot peening is used to enhance fatigue strength, but it is usually neglected by manufacturing design. The main purpose of the present work is to suggest strategies capable of making connection between the process conditions and the fatigue strength. In the present paper, fatigue lives of shot-peened parts were predicted. A new multiaxial HCF model, based on the Crossland criterion, was proposed; it integrates the favourable effects of shot peening that are the combined effect of compressive residual stresses and strain hardening. The plastic strain field accounts for the strain hardening. In order to compute residual stress and equivalent plastic strain profiles due to the repeated impacts, we have modelled and simulated, through a finite element method, the impact of the shot dynamics resulting from the process. The relaxation of induced compressive residual stresses, over the fatigue life, has been considered. For the purpose of spotlighting the capability of the present methodology, the predictions were compared with existing experimental data. This study demonstrates that the single effect of stabilized residual stress is not sufficient to explain the full enhancement of fatigue resistance. The proposed fatigue criterion provides a conservative prediction in terms of endurance limit.

Effects of process combinations of milling, grinding, and polishing on the surface integrity and fatigue life of GH4169 components

The nickel-based superalloy GH4169 is widely applied in the aviation industry due to its outstanding mechanical properties. However, many blades of GH4169 are still produced by milling and manual polishing, which is costly and unreliable. In this article, GH4169 superalloy components manufactured with combination processes of milling, grinding, and polishing were comparatively studied involving surface integrity and fatigue performance. Test results indicate that the final polishing is the most dominant process that influences the high-cycle fatigue life of GH4169 components. Samples produced via cubic boron nitride grinding and numerical control polishing with a diamond-rubber wheel exhibit fatigue limits of 150 MPa higher than the milled and manually polished samples. Cubic boron nitride grinding induces a considerable compressive residual stress profile with a magnitude of -930 MPa and a depth of 200 μm. Milling induces a typical “hook” residual stress profile with 318 MPa at the surface. Polishing affects the machined surface by two ways, the removal effect and the squeezing effect. The squeezing effect induces a shallow compressive residual stress with approximately −1000 MPa, therefore improves the surface condition. However, inevitable omissions, scratches, texture disorders, and knock marks in hand-polishing are the main causes of the unstable high-cycle fatigue life of hand-polished components.

Study on Residual Stress Distribution of 7050 Aluminum Sheet with Groove after Laser Shock Peening

In order to study the residual stress profile of 7050-T7451 aluminum sheet with groove after laser shock peening (LSP), the residual stress distribution was measured. It is shown that the residual stress decreases gradually from the center to the edge of groove; and then there is the minimum value at the edge of the groove bottom surface. By using ABAQUS software to establish three-dimensional finite element model for 7050 aluminum sheet with groove, and the load was applied by VDLOAD subroutine. The finite element analysis was performed and the analysis results were compared with the experimental measurements, in which the both the results agree with each other very well. And then the residual stress distribution of the sheet was analyzed after laser shock peening under different laser processing parameters. It is shown that the residual stress decreases firstly and then increases with the rise of laser power density from 0.84 GW/cm2 to 5.29 GW/cm2. And the residual stress obtains the minimum value -230 MPa at the laser power density of 3.06 GW/cm2. With the increasing of spot diameter from 4 mm to 6 mm, the residual stress increased from -214 MPa to -30 MPa. With the increasing of laser pulse width from 10 ns to 40 ns, the residual stress decreased from -21 MPa to -288 MPa; and the depth of the compressive residual stress increased too. For all simulations under different LSP parameters, the minimum surface residual stress achieved at the bottom surface of the groove as well.

Impact of the Process Parameters, the Measurement Conditions and the Pre-Machining on the Residual Stress State of Deep Rolled Specimens

Mechanical surface treatments, e.g., deep rolling, are widely spread finishing processes due to their ability to enhance the fatigue strength of the treated materials with means of cold working and inducement of favorable compressive residual stresses. Despite of the clear advantages of deep rolling, the controlled generation of compressive residual stresses is still a challenging task, as the process can be influenced by the pre-machining stress state of the treated material. Additionally, the exact characterization of the induced residual stress field is impacted by the specific characteristics of the applied measurement technique. Therefore, this paper is focused on the X-ray diffraction residual stress analysis of deep rolled specimens, pre-machined to achieve rough or polished surface. The deep rolling process was realized as a single-trace to avoid the influence of the other process parameters and the resulted residual stress field on the surface and in depth was investigated. Additionally, the surface residual stress profiles were determined using two different measuring devices to analyze the impact of the different measurement conditions.

On the convergence of solid meshes for the prediction of part distortions due to residual stresses

Residual stresses in rolled plates, used as raw material for the fabrication of aircraft components, arise from manufacturing processes such as rolling, casting, quenching, stretching, and thermal treatments. After each process, the rolled plate has a geometrically stable condition but with internal stresses. However, during part machining an unbalance in the distribution of residual stresses occurs, in special for aircraft components, due to the large amount of material removal throughout the process. This condition of instability leads to component distortions so that any corrective action affects the manufacturing lead-time and production costs. Part distortions are usually predicted by finite element analyses with linear tetrahedral meshes in which the residual stress profiles are applied as a constant value element-wise. In this work, both linear and quadratic solid meshes are employed to address this problem. For this purpose, a Python-based routine is implemented to apply the residual stress profile at the integration points of the elements. Then, finite element simulations of simple geometric configurations (plates and beams) under theoretical and real residual stress distributions are carried out. Performance and effectiveness of two different meshes—tetrahedral and hexahedral (brick-type)—are checked through comparison with results presented by classical plate and beam theories. A general good correlation for the deflections predicted by them is reached.

Role of Steel Plate Thickness on the Residual Stress Formation and Cracking Behavior During Flame Cutting

Thick wear-resistant steel plates are utilized in challenging applications, which require a high hardness and toughness. However, utilization of the thick plates is problematic as they often have nonuniform mechanical properties along the thickness direction due to the manufacturing-induced segregations. In addition, the processing of thick plates commonly involves flame cutting, which causes several challenges. Flame cutting forms a heat-affected zone and generates high residual stresses during the cutting process. In the worst case, flame cutting causes cracking of the cut edge. The aim of this study is to investigate the role of plate thickness on the residual stress formation and cracking behavior when utilizing flame cutting. Residual stress profiles are measured by X-ray diffraction, plates and cut edges and are mechanically tested and characterized by electron microscopy. The results show that thicker plates generate more unfavorable residual stress state during flame cutting. Thick plates also contain segregations, which have decreased mechanical properties. The combination of high residual tensile stresses and segregations increase the risk of cracking during flame cutting. To prevent the cracking, the residual stresses should be lowered by lower cutting speeds and preheating. In addition, manufacturing practices should be aimed at lowering segregation formation in thick plates.

Effect of Laser Peening Process Parameters and Sequences on Residual Stress Profiles

Laser Peening (LP) is a surface modification technology that can induce high residual stresses in a metallic material. The relation between LP process parameters, in particular laser sequences, as well as pulse parameters and the resulting residual stress state was investigated in this study. The residual stress measurements, performed with the hole drilling technique, showed a non-equibiaxial stress profile in laser peened AA2024-T3 samples with a clad layer for certain parameter combinations. Shot overlap and applied energy density were found to be crucial parameters for the characteristic of the observed non-equibiaxial residual stress profile. Furthermore, the investigation showed the importance of the advancing direction, as the advancing direction influences the direction of the higher compressive residual stress component. The direction of higher residual stresses was parallel or orthogonal to the rolling direction of the material. The effect was correlated to the microstructural observation obtained via electron backscattered diffraction. Additionally, for peening with two sequences of different advancing directions, the study showed that the order of applied advancing directions was important for the non-equibiaxiality of the resulting residual stress profile.

Mechanical properties of a laser peened Ti-6Al-4V

The titanium alloy Ti-6Al-4V was subjected to laser peening (without coating) at power densities of 3, 6 and 9 GW cm−2. The cross sectional profiles of microhardness and residual stress indicated softening in the bulk (away from the surface) at power density of 9 GW cm−2. This behavior was analyzed using a combination of Zerilli-Armstrong phenomenological model in conjunction with the concept of adiabatic heating. The implications of this analysis was supported by structural changes in terms of α → β transition (analyzed through synchrotron radiation) and microstructural changes in terms of primary α (equiaxed) to secondary α (lamellar) transformation, which is observed for the first time here. Based on this, optimum levels of peening to improve fatigue lives are suggested through relevant experiments.

Residual Stress Asymmetry in Thin Sheets of Double-Sided Shot Peened Aluminum

The local mechanical properties and residual stresses of a double-sided shot-peened aluminum alloy AA7050-T7451 sheet were measured by nanoindentation and simulated by the finite element method (FEM). The variation of the pileup area around the indentation due to residual stresses, as well as changes in hardness as a function of cold working, was assessed. Numerical simulations were conducted to investigate the residual stress profile. When the indentation contact area was corrected to account for pileup induced from residual stresses, the hardness increased about 10% over the range of depths at which compressive residual stresses exist, indicating some strain hardening did occur. The maximum compressive residual stress for the second shot-peened surface is on the order of 10% higher than the first surface; this is ascribed to the sequencing during the peening process, in which the first side peening influenced the stress throughout the part thickness for these thin plate structures. The ability to couple FEM simulations and rapid experimental assessments of residual stresses and hardness allows for future prediction of part thickness effects in double-sided peening processes.

Analytical modeling of residual stress in orthogonal cutting considering tool edge radius effect

Machining-induced residual stress is a leading cause of machining distortion. Many previous studies have been performed to model the relationship between various impact factors and machined residual stress, such as cutting parameters, lubrication, and cooling conditions etc. While few analytic studies examining the size effect of tool edge radius on residual stress have been performed. In order to better understanding the size effect of tool edge radius on machining-induced residual stress, thermomechanical coupling loading and unloading operations are applied to obtain the machining-induced residual stress on the basis of modeling mechanical loads and thermal loads for cutting with edge radiused cutters. Verification experimental results indicate that the proposed model is effective in judging and analyzing the characteristics of the residual stress profile beneath the machined surface in consideration of the tool edge radius effect. By case studies of Ti-6Al-4V turning those based on the proposed model, it was found that the value of surface residual stress increased with the tool edge radius changed from 0.01 mm to 0.03 mm, and the increased percentage of stresses in cutting and cutting width directions could be 132.6% and 191.1%, respectively. While the peak value of the compressive stress and the depth of the peak value decreased gradually, and the decreased percentages of the peak value of the compressive stress in cutting and cutting width directions are 77.8% and 88.6%. The decreased percentages of the depth of the peak value in cutting and cutting width directions are 47.6% and 63.5%.

Residual stress depth profiling of a coated WC-Co hardmetal - Part I of II: Equi-penetration grazing incidence X-ray diffraction (EP-GIXD) method

The damage behavior of hard coated structures such as used for metalworking tools is influenced by residual stresses since they are superimposed with the load stresses that arise in application. Information on the depth gradient of these residual stresses in a coating's substrate is crucial to understand the evolution of damage in the substrate-coating composite. In the current work, the equi-penetration grazing incidence X-ray diffraction (EP-GIXD) method was adapted for the determination of the residual stress depth profile in the WC-Co hardmetal substrate below an AlCrN-based hard coating. The limits of this method in terms of coating thickness, up to which the EP-GIXD method is applicable to determine the residual stress state in the substrate, were investigated by recording the X-ray absorption in the hard coating in rocking curves. To this end, the diffraction intensity was recorded as a function of the path length in the coating that depends on the incident angle of the X-rays. Subsequently, the obtained residual stress profile was determined as a function of various mean penetration depths selected via the variation of the angle of incidence. The EP-GIXD method facilitates a significant reduction of experimental effort compared to e.g. synchrotron-based approaches for the future study of the residual stress state of substrates in substrate-coating composite structures.

Residual stresses in porcelain tiles. Measurement and process variables assessment

This research addresses the residual stresses phenomenon taking place during the manufacture of porcelain tiles. Residual stresses were quantified by the strain relaxation slotting method. The method is based on the fact that stresses are released when a slot is made leading to a curvature change.Once the method was validated, the impact of process variables such as starting body composition, temperature and cooling rate of firing cycle was investigated. Findings showed that cooling rate was the most influencing variable whereas Young’s modulus of fired specimens also play a significant role. Symmetry of the parabolic residual stress profile denoted homogenous cooling on upper and lower tile surfaces during the cooling step. In addition, it was observed that polishing of a stressed tile gives rise to a decreasing of deformation as a consequence of stress release by mechanical grinding.

Particle Swarm Optimization approach for waterjet cavitation peening

An attempt has been made to solve water jet machining associated with cavitation peening problem through Particle Swarm Optimization (PSO) technique. The swarm initialization is started with Water pressure, stand off-distance and traverse speed. The fitness estimation of PSO is Residual stress, Hardness and Surface profile roughness. These dependent and independent parameters are used in water jet machining to induce beneficial residual stress into the surface layer. These parameters would adversely affect and greatly influenced hardness and surface finish of the machine samples. The position of each particle and conversion of the particle position to velocity are carried out on the PSO algorithm to find the appropriate optimum position of the particle. By following the above procedure, through the PSO algorithm, single order iteration equations are calculated for the independent parameter and it is found to have a correlation of 98% satisfactory limit with the experimental observations. With the developed PSO model, a minimum number of experimental runs will be sufficient to resolve any machining problems that are associated with optimization.

Surface and microstructure characterization of low-frequency vibration-assisted drilling of Ti6Al4V

A continuous curled chip formation with a high thermal load is a critical challenge during conventional drilling process of Ti6Al4V. In addition, adverse side effects will take place on the drilled hole quality, as well as the drill tool performance, which is not acceptable in the aerospace industry. Chip segmentation using low-frequency vibration-assisted drilling (LF-VAD) is a promising technology aimed at reducing the difficulties associated with conventional drilling. Compressive residual stresses, lower cutting zone temperature, higher hole size accuracy, and smoother surface finish are of the main advantages that could be achieved with the interrupted cutting technique. The primary objective of this paper is to investigate the effect of LF-VAD machining parameters on the Ti6Al4V residual stresses, microstructure, and surface integrity, for a wide range of modulation amplitude, feed, and cutting speed, for a new frequency range for the first time. The effect of LF-VAD on the chip morphology and subsurface examination of microstructure, surface, and depth profile of residual stress are examined. The experimental results showed that LF-VAD has a significant influence on the induced residual stress. A 35.8% reduction in the cutting temperature has been observed at the exit surface. This method has improved the residual stress to compressive which has a significant impact on the part fatigue life.

Modeling the Evolution of Residual Stresses in Thermally Sprayed YSZ Coating on Stainless Steel Substrate

This study is based on Eulerian method to model residual stresses for yttrium-stabilized zirconia coating applied to stainless steel substrate. A commercially available finite element software ABAQUS/Explicit is used to conduct this study. Single and multiple-particle impact analyses were carried out, and the residual stress data have been reported. The analysis is performed for two different values of thermal contact resistance and the through-thickness residual stress profiles obtained within the coating for single particle are tensile, while the substrate has a mixture of tensile and compressive residual stresses. For multiple impact model, the residual stress data have been presented for substrate with and without cooling. The residual stresses within the coating without substrate cooling are mostly tensile while the substrate is compressive. The residual stresses within the coating with substrate cooling are mostly tensile with compressive stresses on the top of the coating, while the substrate consists of compressive stresses. The obtained residual stresses are compared with experimental and analytical data.