Residual Stress Values Research Articles

ОЦІНЮВАННЯ РІВНЯ ТЕРМІЧНИХ НАПРУЖЕНЬ В ОКСИДНИХ ТОНКИХ ПЛІВКАХ

The results of estimation of the nature and magnitude of residual thermal stresses in CuO oxide layer synthesized on a substrate of pure copper using a known analytical model for calculating thermal stresses in single-layer coatings are presented. Thermal stresses can lead to deformations and destruction of thin-film structures and coatings, shortages and reduced quality of parts on which they are applied. The main technological parameters, on which the values of thermal stresses depend, are the operating temperatures of the process of formation of thin-film oxide layers. After the synthesis process, the coated substrates are cooled to ambient temperature. This cooling leads to thermal residual stresses. In the case where the coefficient of thermal expansion of the material of the oxide layer is much less than the coefficient of thermal expansion of the substrate material, in the CuO layer compressive residual stresses generete, while in the Cu substrate – tensile stresses. The stress-strain state during the cooling of the thin film/substrate system, which is free from external forces, was investigated. The mathematical model used the assumption that the resulting deformations do not exceed the elastic limit (the residual stresses lie in the region of elastic deformations), and the temperature gradient in the thickness of the materials does not change. It should also be noted that the values of thermal expansion coefficients, modulus of elasticity and Poisson's ratios are constant values and do not depend on temperature changes. The paper presents the main analytical dependences of thermal stresses on the physical and mechanical properties of the coating materials and the substrate. Based on the results of calculations, a graph of the dependence of thermal stresses of the coating-substrate system depending on the temperature of synthesis of oxide layers was developed. Thermal stresses are one of the components of the total residual stresses operating in the film/coating system. The obtained results on the values of residual stresses can be used to prevent the deformation and failure of thin films and coatings, as well as to predict the characteristics of the surface layers.

Modelling and Characterisation of Residual Stress of SiC-Ti3C2Tx MXene Composites Sintered via Spark Plasma Sintering Method.

This article presents an attempt to determine the effect of the MXene phase addition and its decomposition during sintering with the use of the spark plasma sintering method on mechanical properties and residual stress of silicon carbide based composites. For this purpose, the unreinforced silicon carbide sinter and the silicon carbide composite with the addition of 2 wt.% of Ti3C2Tx were tested. The results showed a significant increase of fracture toughness and hardness for composite, respectively 36% and 13%. The numerical study involving this novel method of modelling shows the presence of a complex state of stress in the material, which is related to the anisotropic properties of graphitic carbon structures formed during sintering. An attempt to determine the actual values of residual stress in the tested materials using Raman spectroscopy was also made. These tests showed a good correlation with the constructed numerical model and confirmed the presence of a complex state of residual stress.

Thermoelastic state during electrofusion welding of polyethylene pipes at different ambient temperatures

The problem of welding polyethylene pipes used in the mining industry at low ambient temperatures is considered The numerical solution of a thermoelastic problem revealed the distinctive features of thermal and stress-strain states of weld connections of polyethylene pipes using embedded heater couplings at different ambient temperatures. It is found that in low-temperature conditions, the size of the melted zone is considerably smaller than during welding at permissible temperatures. In this regard, the pressure insufficient for high-quality welding is created between the coupling and the pipe. It is also shown that at the time of melt crystallization, the maximum values of stresses and strains during welding at low temperatures are higher than during welding in the permissible temperature range, which causes high values of residual stresses. The results obtained can be used in the development of low temperature welding technology.

Evaluation of laser shock peening process parameters incorporating Almen strip deflections

Engineering of component surfaces using Laser Shock Peening (LSP) requires optimisation of key process parameters to enhance performance through the generation of beneficial compressive residual stresses. Quantification of residual stress fields typically requires considerable experimental resources involving multiple complementary techniques to obtain reliable measurements through the depth of the target material. LSP induced plastic strains lead to the formation of residual stresses and cause deformation of thin components. This effect is routinely used in the assessment of mechanical Shot Peening (SP) where distortion coupons, called Almen strips, correlate the peening intensity to process parameters. This study explores the extension of this Almen strip concept to facilitate the quick assessment of LSP parameters for aluminium alloy 6056-T4 aeronautical structural applications. Direct measurements of the resulting LSP residual stresses have been performed using Synchrotron X-Ray Diffraction, Neutron Diffraction, and Incremental Hole Drilling, complemented by analyses of surface integrity and sub-surface modifications. It has been found that the attained near-surface compressive residual stress values and depths are strongly dependent on laser power intensity and spot coverage, whilst surface roughness and microhardness are mostly independent of the LSP parameters. Optimal parameter selection should therefore be primarily focused on the required residual stress field. A direct correlation has been observed between the magnitudes of LSP Almen distortions and the residual stresses. This qualifies extending the deflection based approach to be used as a quick, simple and effective qualitative screening technique of LSP process parameters, such as the laser power intensity saturation.

Influence of Deposition Strategies on Residual Stress in Wire + Arc Additive Manufactured Titanium Ti-6Al-4V

Wire + arc additive manufacturing (WAAM) is a modern manufacturing process that has opened new possibilities for rapid builds and reductions in material wastage. This paper explores residual stress in WAAM Ti-6Al-4V walls built using three different deposition strategies: single bead, parallel path, and oscillation path. The effect of interlayer hammer peening and interlayer temperature was investigated for the single bead walls. We also examined the residual stress in compact-tension (C(T)) coupons extracted from large builds (walls) with crack orientation either parallel with or perpendicular to the build direction. This type of sample is often used for the measurement of the fatigue crack growth rate. The contour method was used for experimental determinations of residual stress. In addtion, residual stress in the C(T) coupons was estimated by finite element (FE) analysis. A good agreement was achieved between the contour method and FE analysis. The oscillation-path wall had the lowest residual stress values. For the single bead walls built with various process conditions, residual stress was significantly reduced after removing the substrate. A interlayer temperature of 110 °C resulted in much higher residual stress values in the wall (both tensile and compressive) compared to the continuous build, with much higher interlayer temperature.

Numerical prediction and experimental investigation of residual stresses in sequential milling of GH4169 considering initial stress effect

Residual stresses affect the service life and cause the deformation of machined parts. Therefore, the study on the development of residual stresses during machining operation is very important. For this, analytical and numerical models have been developed to predict the residual stresses for single-step machining operation. However, the parts are usually machined with a serial of production processes. A numerical model for predicting residual stress in sequential side milling GH4169, considering initial stress, was proposed in this research. The initial residual stress distribution due to previous-step milling was considered in the proposed model. It was assumed that this initial residual stress value changed with the depth from the machined surface, while the residual stress on the identical horizontal plane was assumed with uniform distribution. The proposed numerical simulation model could predict the stress value of the machined surface, the stress value of the compression valley, and the residual stress distribution in the depth direction beneath the machined surface with high accuracy. Experimental investigations of sequential side milling GH4169 were conducted and the generated residual stresses were measured. The distribution trend and influence rule of residual stress between two sequential milling steps were analyzed. The residual stress distribution beneath the surface showed a spoon-shaped pattern. The thickness of the residual stress influence layer (RSIL) after the current milling step was affected by the depth of cut and the RSIL thickness of the previous milling step. The numerical model could predict the thickness of RSIL and optimize the depth of cut in sequential side milling.

Experimental implementation of the laser shock peening method aimed at an increase in the fatigue properties of metals

The study is aimed at the development and implementation of an experimental setup for treating metal parts with complex geometry to induce compressive residual stresses in the surface layers. Modern methods of surface treatment demonstrated the possibility of increasing the durability of parts by several times through creation of high-amplitude residual compressive stresses. We managed to form the residual compressive stresses up to a depth of 1 mm using the titanium alloy specimens. The developed installation consists of a solid-state laser with a pulse energy of up to 10 J, a six-axis robot manipulator, and a system for measuring residual stresses by hole drilling method. The processing is realized in automatic mode with the possibility of continuous change of specimens. The geometry of parts and processing features are worked out on a digital three-dimensional model of the part. A number of tests have been carried out to reveal the dependence of the values of residual stresses on the processing conditions and demonstrate the necessity of numerical analysis and preliminary modeling of the process of laser shock peening. The distribution of residual stresses was measured by hole drilling method in the specimens before and after laser shock peening under various processing conditions, and the profiles of these stresses in depth were plotted. It is shown that along with the pulse power, the value and distribution of residual stresses are significantly affected by the number of repeated passes, the overlap degree, and the technology of preliminary preparation of the specimen surface. The analysis made it possible to choose the optimal processing mode for titanium alloys providing the values of residual compressive stresses up to 1 GPa.

Evaluation and Origin of Residual Stress in Hybrid Metal and Extrusion Bonding and Comparison with Friction Stir Welding

Hybrid metal and extrusion bonding (HYB) is an emerging solid-state welding technique that was developed about ten years ago. HYB exploits the fundamental idea of the well-established friction stir welding (FSW) technology, but a filler material is employed to enhance control of the microstructure and the mechanical properties of the joint. HYB and FSW allow joining to be performed at lower temperatures than classical fusion welding methods. Still, thermal gradient effects seem impossible to be entirely avoided, thus leading to residual stress within the weld region and neighbouring material. Although the FSW-induced residual stress evaluation has been extensively studied and understood, the evaluation and interpretation of HYB-induced residual stress have not been tackled so far. In the present paper, a quantitative investigation on residual stress and its origin in HYB was carried out for the first time. Specifically, a 4 mm thick AA6082-T6 HYB and a 4 mm thick AA6082-T6 FSW butt welds were considered. For the particular case of HYB, an AA6082-T4 was used as the filler material. In both cases, the full-field longitudinal residual stress was experimentally assessed using the Contour Method. The results showed that the HYB joint yields a higher magnitude of tensile residual stress compared to that of the FSW counterpart. A physical explanation for this difference in magnitude was attributed to the lower yield stress point exhibited by the filler material. Furthermore, the analysis revealed peak values of residual stress as high as 205±25 MPa and 165±15 MPa, for the HYB and FSW joint, respectively. Despite this, a similar distribution of residual stress across the weld was observed in both cases. An additional qualitative analysis on the transverse distortion of the welds outlined a pronounced undesired “V-like” deformation of the HYB joint of approximately 1.4°. By contrast, the FSW joint seemed not to show any perceptible bend.

Effect of the sector radius of a workpiece-deforming tool on the stress-strain state in the contact zone with a cylindrical surface

This paper aims to determine the effect of the sector radius of a workpiece-deforming tool on the stress-strain state in the center of elastoplastic deformation and residual stresses in the hardened zone of the surface layer of cylindrical workpieces. A mathematical model of local loading was constructed using the finite element method and AN-SYS software. This model was used to determine the values of temporary and residual stresses and deformations, as well as the depth of plastic zone, depending on the sector radius of the working tool. The simulation results showed that, under the same loading of a cylindrical surface, working tools with different sector radii create different maximum tempo-rary and residual stresses. An assessment of the stress state was carried out for situations when the surface layer of a product is treated by workpiece-deforming tools with a different shape of the working edge. It was shown that, compared to a flat tool, a decrease in the radius of the working sector from 125 to 25 mm leads to an increase in the maximum temporary and residual stresses by 1.2–1.5 times, while the plastic zone depth increases by 1.5–2.4 times. The use of a working tool with a flat surface for hardening a cylindrical workpiece ensures minimal temporary residual stresses, com-pared to those produced by a working tool with a curved surface. A decrease in the radius of the working sector leads to an increase in temporary residual stresses by 2–7%. The plastic zone depth ranges from 1.65 to 2.55 mm when chang-ing the sector radius of the working tool.

The Effect of Combined Processing on Residual Stresses in the Surface Layer of Power Plant Parts.

The purpose of this research was to analyze the change in residual stresses in the surface layer of steel samples taking into account the technological heredity effect on the value and sign of residual stresses. An installation of combined processing was developed. Combined processing consists of sequentially performing electromechanical processing and diamond smoothing. All areas of the samples were studied—after machining (i.e., in the initial state), after electromechanical processing, and after diamond smoothing. The research shows that the sign and value of residual stresses are significantly affected by the combined processing modes. The main parameters of the surface layer are formed at the final stage of the combined processing–diamond smoothing. This paper gives recommendations on the use of combined processing for power plant parts.

Determination of the stress-deformed state of cylindrical parts at circular oscillation of a sectorial working tool

It is described the effect of the frequency of circular oscillations of a sectorial working tool on the stressstrain state of cylindrical parts. As a result of computer modeling, it was revealed that under the same loading conditions, the action of a working tool with different frequencies of circular oscillations creates different values of temporary and residual stresses. In the case of movement in one direction of the tool and the workpiece, the minimum value of stresses is formed, and with their oncoming movement, the value of the maximum stresses increases by 15...40 %. The resulting value of the residual stresses generally increases. With an increase in the frequency of circular oscillation of the working tool, the intensity of residual stresses increases by 1.2...2 times. The intensity of deformation changes in direct proportion to the value of the frequency of the circular oscillation and the depth of plastic deformation reaches 2.1...2.8 mm.

РАСЧЕТНОЕ ПРОГНОЗИРОВАНИЕ ТЕХНОЛОГИЧЕСКИХ ОСТАТОЧНЫХ ДЕФОРМАЦИЙ ЛОПАТОК ГТД НА ЭТАПЕ КОНЦЕВОГО ФРЕЗЕРОВАНИЯ

The article presents a technique that makes it possible to predict the technological residual deformations of GTE blades obtained at the stages of end milling as a result of the effect of residual stresses. The first part of the technique makes it possible to determine the magnitude, bijugat and character of the residual stresses distribution formed in the surface layer of the workpieces in the operations of end milling. The adequacy of the technique was verified by investigating the convergence of the numerical computation results with the results of field experiments. As a result of the research, a power-law dependence was obtained, which makes it possible to determine the value of the maximum circumferential residual stresses depending on the parameters of the end milling processing mode. The second part of the technique makes it possible to determine the residual deformations of the GTE blade based on the residual stress distribution diagrams obtained when using of the first part of the technique or obtained on the basis of field experimental investigations. Also, power-law dependences are obtained in this work, which make it possible to determine the value of the maximum deviations of the control sections of the investigated GTE blade, depending on the parameters of the end milling mode.

Stress-strain state of surface layer under reversible surface plastic deformation of machine parts

The article considers an approach to increasing the stress state in the elastic-plastic deformation zone during surface plastic deformation. The technical idea of solving the problem is based on the complication of the kinematics of a two-radius roller. To achieve this goal, the finite element method based on the ANSYS computer program was used, which makes it possible to determine the values of temporary, residual stresses and strains for different schemes of reversible surface plastic deformation with a two-radius roller. It has been established that the greatest influence on the stress-strain state in the deformation zone is exerted by the scheme of reverse rotation of a two-radius roller located at an angle of 45 degrees relative to the direction of movement, and the least effect is when hardening with a two-radius roller, the axis of rotation of which coincides with the direction of movement.

Mechanical strain and electric-field modulation of graphene transistors integrated on MEMS cantilevers

This work proposes a structure which allows characterization of graphene monolayers under combined electric field and mechanical strain modulation. Our approach is based on a cantilever integrated into a two-dimensional graphene-based Field effect transistor (FET). This allows us to change graphene properties either separately or together via two methods. The first way involves electric field induced by the gate. The second is induction of mechanical strain caused by external force pushing the cantilever up or down. We fabricated devices using silicon-on-insulator wafer with practically zero value of residual stress and a high-quality dielectric layer which allowed us to precisely characterize structures using both mentioned stimuli. We used the electric field/strain interplay to control resistivity and position of the charge neutrality point often described as the Dirac point of graphene. Furthermore, values of mechanical stress can be obtained during the preparation of thin films, which enables the cantilever to bend after the structure is released. Our device demonstrates a novel method of tuning the physical properties of graphene in silicon and/or complementary metal-oxide-semiconductor technology and is thus promising for tunable physical or chemical sensors.

Comparison of Taguchi Method and Response Surface Methodology in Determining Optimal Parameters for Welding Two Metal Plates

Welding technology play important role in manufacturing and gas metal arc welding is one of the most popular welding methods. There are many input parameters that affect the quality of the welding seam such as welding current, welding voltage, welding speed, etc. One of the problems in controlling welding robot is determining the optimal parameters that maximize the quality of welding. There are several designs of experiment techniques can be used to get the desired results with small number of experiments. In this paper, Taguchi method and response surface methodology are chosen to estimate the value of residual stresses of the seam path of welding two metal plates. In case of response surface methodology, both Box-Behnken design and central composite design are used in determining the optimal parameters. The estimation of residual stresses is done by ABAQUS software. The comparison among the designs is done and many conclusions about the optimal parameters and mathematical model are presented.

Optimization of fused deposition modelling process parameters and the effect on residual stresses of built parts

Fused deposition modelling (FDM) is one of the most used additive manufacturing techniques for the fabrication of functional parts from composite filaments. Despite the widespread application spectra, FDM is still limited in its applicability due to inherent problems, one of which is the significant accumulation of residual stresses during part building. Residual stresses are generated due to thermo-cyclic loading in subsequent layers. The effect of residual stresses is significant for the mechanical integrity of the manufactured parts. Since it is impossible to manufacture parts without internal residual stresses, it is prudent to optimize the process parameters that would result in minimal residual stresses. In this study, Digimat additive manufacturing 2020 software with Taguchi design of experiment was used to predict the effect of printing temperature, layer thickness, and print speed on the generated residual stresses. Generic algorithm was used to determine the optimum combination levels for the minimum residual stresses. Results showed a near convergence between simulation and experimental residual stress values with an error of 3.7 %. The mechanical properties of 3D printed carbon fiber composite products were found to have tensile strength; 71.48 MPa, compressive strength; 135.8 MPa, Young’s Modulus; 7.6 GPa, and percentage elongation; 1.86 %. These properties fell within the acceptable range for the actual parts to be replaced. The results of this study will serve as a pragmatic approach to 3D printing of components devoid of trial and error strategies that have currently slowed the adoption of the FDM technique as a rapid prototyping tool for enhanced manufacturing.

Optimization of the sintering temperature, cooling time and grain size parameters to reduce residual stresses of copper-aluminum functionally graded material using response surface methodology

One of the urgent needs for the medical, aerospace and military industries is to combine materials with heat-resistant as well as flexible structures. To create such a property, a ceramic must be placed next to metal. FGM materials have such a property in terms of thickness. Functionally graded materials (FGM) are examples of materials with different properties in the thickness direction. In the functionally graded materials, different properties can be created, by changing the percent weight of materials in each layer. It is very important to study the number of residual stresses in these materials due to the fact that several materials with different properties are combined with each other. The purpose of this study is to investigate the effect of production parameters on the number of residual stresses in the aluminum-copper FGM part and also to optimize the production process of these materials. The results indicate that the number of residual stresses decreases with increasing the sintering temperature, cooling time of the sample as well as uniformity along the thickness. In the experiments, the maximum residual stress was 171 MPa, which was obtained for a grain size of 100 microns, sintering temperature of 600°C and cooling time of 24 h and the minimum value of pressure residual stress was 120 MPa, which was obtained for grain size of 20 microns, sintering temperature of 900°C and cooling time of 48 h. Also, finite element modeling of the process was performed and shown a good agreement with experimental results.

Comparative Multi-Modal, Multi-Scale Residual Stress Evaluation in SLM 3D-Printed Al-Si-Mg Alloy (RS-300) Parts

SLM additive manufacturing has demonstrated great potential for aerospace applications when structural elements of individual design and/or complex shape need to be promptly supplied. 3D-printable AlSi10Mg (RS-300) alloy is widely used for the fabrication of different structures in the aerospace industry. The importance of the evaluation of residual stresses that arise as a result of the 3D-printing process’ complex thermal history is widely discussed in literature, but systematic assessment remains lacking for their magnitude, spatial distribution, and comparative analysis of different evaluation techniques. In this study, we report the results of a systematic study of residual stresses in 3D-printed double tower shaped samples using several approaches: the contour method, blind hole drilling laser speckle interferometry, X-ray diffraction, and Xe pFIB-DIC micro-ring-core milling analysis. We show that a high level of tensile and compressive residual stresses is inherited from SLM 3D-printing and retained for longer than 6 months. The stresses vary (from −80 to +180 MPa) over a significant proportion of the material yield stress (from −⅓ to ¾). All residual stress evaluation techniques considered returned comparable values of residual stresses, regardless of dramatically different dimensional scales, which ranged from millimeters for the contour method, laser speckle interferometry, and XRD down to small fractions of a mm (70 μm) for Xe pFIB-DIC ring-core drilling. The use of residual stress evaluation is discussed in the context of optimizing printing strategies to enhance mechanical performance and long-term durability.

Effect of Al2TiO5 Content and Sintering Temperature on the Microstructure and Residual Stress of Al2O3-Al2TiO5 Ceramic Composites.

A series of Al2O3–Al2TiO5 ceramic composites with different Al2TiO5 contents (10 and 40 vol.%) fabricated at different sintering temperatures (1450 and 1550 °C) was studied in the present work. The microstructure, crystallite structure, and through-thickness residual stress of these composites were investigated by scanning electron microscopy, X-ray diffraction, time-of-flight neutron diffraction, and Rietveld analysis. Lattice parameter variations and individual peak shifts were analyzed to calculate the mean phase stresses in the Al2O3 matrix and Al2TiO5 particulates as well as the peak-specific residual stresses for different hkl reflections of each phase. The results showed that the microstructure of the composites was affected by the Al2TiO5 content and sintering temperature. Moreover, as the Al2TiO5 grain size increased, microcracking occurred, resulting in decreased flexure strength. The sintering temperatures at 1450 and 1550 °C ensured the complete formation of Al2TiO5 during the reaction sintering and the subsequent cooling of Al2O3–Al2TiO5 composites. Some decomposition of AT occurred at the sintering temperature of 1550 °C. The mean phase residual stresses in Al2TiO5 particulates are tensile, and those in the Al2O3 matrix are compressive, with virtually flat through-thickness residual stress profiles in bulk samples. Owing to the thermal expansion anisotropy in the individual phase, the sign and magnitude of peak-specific residual stress values highly depend on individual hkl reflection. Both mean phase and peak-specific residual stresses were found to be dependent on the Al2TiO5 content and sintering temperature of Al2O3–Al2TiO5 composites, since the different developed microstructures can produce stress-relief microcracks. The present work is beneficial for developing Al2O3–Al2TiO5 composites with controlled microstructure and residual stress, which are crucial for achieving the desired thermal and mechanical properties.

Influence of the heat transfer coefficient on the level of residual stress after heat treatment of the VVER-1000 reactor baffle

Background. Improvement of the methodology for the computational analysis of residual stresses in the structural elements of the reactor is an integral part of the work when extending the service life of NPP power units.
 Objective. Determine the value of residual technological stress arising in the baffle of a VVER-1000 reactor during welding and postweld heat treatment according to the austenitizing mode. To evaluate the effect of considering the dependence of the heat transfer coefficient on the temperature of the baffle surface at cooling in air during heat treatment.
 Methods. Numerical modeling of the stress-strain state of the baffle during welding and postweld heat treatment was carried out using the finite element method.
 Results. It was determined that in the process of heat treatment according to the austenitizing mode, the residual welding stress in the baffle are almost completely relaxed. Due to the high temperature gradient during rapid cooling in air after heating in the process of austenitization, new rather high residual stresses are formed in the zones of the baffle with the greatest metal thickness.
 Conclusions. Based on the results of the investigation, a high level of residual technological stress was determined, which should be considered when calculating the justification for extending the service life of the VVER-1000 reactor baffle.