Formation Of Residual Stresses Research Articles

WITHDRAWN: A comprehensive analysis on assessing and controlling of residual stresses in friction stir welded joints

Residual stresses is one of the vital factors in deciding the performance of all the machining and joining process. Friction Stir Welding (FSW) is belong to the family of solid-state joining processes encounters the problem of residual stresses formation during the metal joining process. Residual stresses in the welded area produces fatigue and stress corrosion cracks leads to premature failure of the components/parts. Residual stress could be either in the form of tensile or compressive or combination of both. In the elastic region, compressive and tensile stress balances each other and maintains equilibrium state. The welded part subjected to cyclic loads and temperature histories creates challenging working condition. The control of residual stresses is now becoming challenging task during manufacturing process and also during service of the end product. This review discusses the source of residual stresses and possible way to measure numerically and experimentally.

Effects of microstructure on the evolution of dynamic damage of Fe50Mn30Co10Cr10 high entropy alloy

The Fe50Mn30Co10Cr10 high-entropy alloy (HEA) was subjected to plate impact loading with a single-stage light gas gun and the Doppler pin system (DPS) was used to measure the velocity of free surface particles of the sample during loading. The effects of microstructure on the evolution of spallation of the Fe50Mn30Co10Cr10 HEA were investigated by means of electron back scattered diffraction (EBSD), optical microscope (OM) and X-ray diffraction (XRD) techniques. The results showed that the voids are neither nucleated at the martensite (M)/matrix interface nor nucleated in the M aggregated area (M area) with high impact resistance as predicted by impact dynamics, instead, voids nucleated inside the matrix phase with low impact resistance. The reason is that the lattice expansion during M transformation leads to the formation of compressive residual stress at the M/matrix interface as well as M area and tensile residual stress in the matrix, which promoted the preferential nucleation of voids in the matrix. Void nucleation in the matrix was not random: the tri-junction of general high angle grain boundaries (HAGBs) and the grain boundaries of adjacent grains with a large difference in Taylor Factor (TF) value were prone to stress concentration under tensile loading, which were the priority position for void nucleation. The void nucleation was inhibited by twin boundary (TB) due to its stable structure and low energy. However, the intersections of HAGBs and termination TB are the possible position for void nucleation due to its high interface energy. The compressive residual stress at the M/matrix interface and inside of M area has a closure effect on the microcrack, which caused the microcrack avoided the M area and propagated in the matrix and finally stopped at the M/matrix interface.

INCREASING THE DURABILITY OF DETAILS TO WORK UNDER REPEATABLE LOADS

The article presents the results of the development of processes to improve the performance of parts operating under repeated variable loads, taking into account the reasonable parameters of surface plastic deformation (SPD) and cold gas-dynamic spraying of coatings. The influence on the parameters of the working surface layer, the nature of the distribution of the stress-strain state of the surface layer of material and residual compressive stresses, as well as the values of the used resource of plasticity of the surface layer of the workpiece, the parameters of the SPD process. The article shows that the main factor in the formation of residual compressive stresses during SPD is the decrease in the density of the surface layer of the workpiece, which is associated with the use of the plasticity resource. The model of calculation of the used resource of plasticity of material of preparation at SPD which allows to provide the improved quality of a surface layer of details is offered. A method of moving the workpiece layers with maximum hardening and residual compression stresses to the surface of the part by applying a deforming tool of reduced size in the following passes with coating the surface of the part with gas-dynamic spraying before SPD. Cold gas-dynamic coating by spraying, in contrast to most known gas-thermal coating methods that take place under significant temperature effects on the surface of the part, which is unacceptable for surfaces treated by SPD methods, provides a permissible temperature regime for creating special auxiliary coatings while preserving surface properties SPD. The technology of gas-dynamic coating by spraying includes heating the compressed gas (air), directing it into the nozzle and forming in this nozzle supersonic air-powder flow, sprayed material (copper, aluminum), acceleration of this powder material to supersonic speeds and directing it to the surface of the processed product. As a result, a special auxiliary coating (copper or aluminum) is formed on the surface of the product, which improves the parameters of the SPD process.

Study of residual stress and microstructural evolution in as-deposited and inter-pass rolled wire plus arc additively manufactured Inconel 718 alloy after ageing treatment

The manufacture of structural components made from nickel-based super alloys would benefit from the commercial advantages of Wire + Arc Additive Manufacturing (WAAM), as it is commonly expensive to process using other conventional techniques. The two major challenges of WAAM are process residual stress and undesired microstructure. Residual stress causes part distortion and build failures, while the as-deposited microstructure does not allow the common heat-treatment to be effective in achieving the desired mechanical properties. This paper focuses on understanding the microstructural features, phase formation and three-dimensional residual stress state variation in as-deposited and inter-pass rolled conditions and after solutionising, quenching and ageing. The thermal history from successive deposition and cold working were correlated to the phase formation and macro residual stress formation and subsequent evolution. The {311} family of crystallographic planes were used as atomic strain gauge to determine the macrostrain and analysis of three dimensional stress state in different processing conditions. The measured strain were corrected for the compositional variation by measuring EDM machined d0 specimens manufactured under similar processing conditions. While the as-deposited part show significant stress redistribution and distortion after removal from the main fixture, inter-pass rolling was found to reduce part distortion significantly, the residual stress profile after inter-pass rolling showed highest tensile magnitude near the substrate while near the top of the deposit it was compressive as can be expected from the rolling process. The other two beneficial effects of inter-pass rolling on the microstructure are mitigation of the formation of undesired Laves-phase, thereby improving the response to solution treatment and aging together with significantly reduced grain size and texture. The application of inter-pass rolling reduces the potential part complexity, which however does not prevent the manufacture of common candidate parts, which are typically 1-to-1 replacements of forged, cast or machined from solid.

Customization of residual stress induced in cold spray printing

Abstract It is generally believed that because of deposition at a temperature lower than the melting point, and high impact velocity of particles in cold spray printing, beneficial compressive residual stresses are induced in the substrate and coating. We have examined this general belief by identifying four major factors influencing the formation of residual stresses: coating and impact-induced temperatures, thermal mismatch of coat and substrate, heat transfer rate, and impact peening effect. A series of experiments is developed to allow studying these effects separately and to investigate their interactions. It is concluded that the heat input and heat transfer rate are the key controlling factors in the sign of the residual stress. Furthermore, we show that one can control the formation of residual stress to a desirable pattern, i.e., compressive in both the coating and the substrate near the interface. Using such parameters, two distinct residual stresses, tensile and compressive, were produced in the Al7075 coated AZ31B sheet. Further, the quality of the two coatings is measured through computerized tomography, surface roughness, and hardness measurements. It is shown that the density and hardness of the compressive samples are higher, while the roughness is lower than the tensile sample.

Impact of grinding wheel specification on surface integrity and residual stress when grinding Inconel 718

The grinding process is often maligned by grinding burn; which refers to many unwanted effects, including residual stress formation. This paper presents an overview of the role of grinding wheel technologies in the surface response and residual stress formation of thin section Inconel 718. Using production standard equipment, conventional abrasive vitrified, and super abrasive electroplated wheel technologies were evaluated in initial comparative trials. Results revealed the dominant residual stress profiles, which manifested as measurable distortion and the thermo-mechanical impact of grinding, such as softening. Following this, a parametric study was carried out using cubic boron nitride super abrasive electroplated wheels to investigate the interaction of grinding parameters on the generated output. It was shown that at increased grinding aggressions, tensile stress regimes increased resulting in increased distortion magnitudes. The study highlights the importance of assessing residual stress formation when manipulating both wheel technologies and grinding parameters. It is envisaged that with additional assessment, a route to an engineered residual stress profile might be achieved.

Determination and Validation of Residual Stresses in CFRP/Metal Hybrid Components Using the Incremental Hole Drilling Method

Lightweight materials contribute to an efficient decrease in fuel consumption in the automotive and aircraft industries. Hybrid components made of metal and carbon fiber-reinforced plastics (CFRP) have a high potential in lightweight applications due to their high strength-to-weight ratio. For cost-effective processing of hybrid materials, advanced manufacturing processes such as the prepreg-press-technology have been developed, in which the bonding between a metallic component and a fiber compound is exclusively realized in the forming process. However, upon processing of these hybrid components at elevated temperature, the difference in thermal expansion coefficients of the two materials leads to the formation of tensile residual stresses upon cooling. It is well known that these tensile residual stresses can be detrimentally effective with respect to the durability of a hybrid component. The objective of this work is to accurately measure and analyze residual stresses in hybrid components made of unidirectional CFRP and steel through the incremental hole drilling method. Within this study, the evaluation formalism for orthotropic materials is employed for measuring non-uniform residual stresses in hybrid materials. In order to improve the measurement accuracy, a customized strain gauge with eight grids is employed and a drilling increment size of only 20 µm is utilized. The influence of the angle between the strain gauge rosette and the fiber direction on the evaluation of the residual stresses is investigated. In order to evaluate the reliability of the results determined, a bending test applying a well-defined load is carried out. By direct comparison of the experimentally determined stresses and stress values calculated by the finite element method, the applicability of the hole drilling method for robust determination of residual stresses in CFRP/metal hybrid components is finally validated.

Separation of the Formation Mechanisms of Residual Stresses in LPBF 316L

Rapid cooling rates and steep temperature gradients are characteristic of additively manufactured parts and important factors for the residual stress formation. This study examined the influence of heat accumulation on the distribution of residual stress in two prisms produced by Laser Powder Bed Fusion (LPBF) of austenitic stainless steel 316L. The layers of the prisms were exposed using two different border fill scan strategies: one scanned from the centre to the perimeter and the other from the perimeter to the centre. The goal was to reveal the effect of different heat inputs on samples featuring the same solidification shrinkage. Residual stress was characterised in one plane perpendicular to the building direction at the mid height using Neutron and Lab X-ray diffraction. Thermography data obtained during the build process were analysed in order to correlate the cooling rates and apparent surface temperatures with the residual stress results. Optical microscopy and micro computed tomography were used to correlate defect populations with the residual stress distribution. The two scanning strategies led to residual stress distributions that were typical for additively manufactured components: compressive stresses in the bulk and tensile stresses at the surface. However, due to the different heat accumulation, the maximum residual stress levels differed. We concluded that solidification shrinkage plays a major role in determining the shape of the residual stress distribution, while the temperature gradient mechanism appears to determine the magnitude of peak residual stresses.

Surface integrity analysis of grinding on ductile iron

Ductile iron (DI) is a widely used material and one of the most largely casts produced. Advances in the understanding of the characteristics and behavior of this material have led to the development of parts with dimensions and shapes close to the final ones, and components with different thickness sections, including thin wall. When certain tolerances of shape and dimension have to be met, an appropriate machining process such as grinding must be chosen. This type of process produces high local efforts and hence a great amount of heat in the contact zone. Nowadays, there is scarce information on the effects of grinding on the surface integrity of DI. A comparative study of the surface finish and surface integrity of DI with different microstructures and nodule counts (NC) under grinding conditions was performed. All ground surfaces exhibited a good finish, and their surface roughness was within the expected range for grinding operations. Microstructure alterations as well as strains were studied and related to hardness alterations. The role played by mechanical and thermal effects on residual stress profiles was analyzed. A clear relationship between distortion and residual stress formation during the grinding process was established.

Residual Stress: Both Friend and Foe

Abstract Residual stress exists in all classes of materials and significantly impacts many facets of product design and manufacturing. This article reviews residual stress formation, types of stresses, and measurement techniques. ASM International is launching a technical committee on residual stress to enable industry-wide collabration and to advance the science of this important phenomenon.

CASE STUDY: Failure analysis of induced draft fan after serious inspection by overlay welding

IDF or Induced draft fans are one of the components in a steam power plant that functions to dispose of the combustion gases of coal in the steam generator. IDF operation is inseparable from the failure problem, both on the fan or IDF shaft. During operation, real-time monitoring of IDF is an important factor to determine technical conditions and detect failures at an early stage. When something that can cause failure is detected, an inspection is needed to ensure that the IDF components continue to function properly, such as First-Year Inspection, Simple Inspection, Mean Inspection, and Serious Inspection.The failures of IDF occur after serious inspection, cracks occur on the IDF shaft, where cracks occur not in areas that have high-stress concentrations. This failure on the IDF-Shaft does not reach the final fracture because of the detection of the vibration monitoring device so that when the trend rises at a certain peak, the IDF operation will shut down automatically. The failure occurs due to residual stress in the HAZ region generated by the welding process at making the impeller. The formation of residual stresses in the welding process, welding metals, and parent metals undergo a thermal cycle of heating and cooling. This thermal cycle causes stresses and stresses which in turn result in residual stresses and distortion. Residual stress can cause shaking, reduce fatigue resistance, welding strength, and corrosion resistance.

INCREASING OF THE DURABILITY OF DETAILS WORKING UNDER REPEATABLE- LOADS

The article develops processes of increase the durability of parts operating under repeated loads, by justifying the parameters of surface plastic deformation (SPD) and cold gas-dynamic coating. The influence on the depth of the reinforced surface layer, the nature of the distribution of the stress-strain state of the material and residual compressive stresses, as well as the value of the used plasticity of the metal, the parameters of the SPD process. The hypothesis is substantiated that the main factor in the formation of residual compressive stresses during SPD is the decrease in metal density, which is associated with the use of the plasticity resource. The model of definition of the used resource of plasticity of metals at SPD is developed, that allows to provide qualitative characteristics of a surface layer of details. Methods for shifting the layer with maximum hardening and residual compressive stresses to the surface of the part by using a deformable tool of smaller dimensions in subsequent passes and gas-dynamic coating before SPD. The vast majority of traditional gas-thermal coating methods occur at significant temperature effects on the surface of the part, which is unacceptable for the surface treated by SPD methods. Cold gas-dynamic spraying provides an allowable temperature regime for the creation of special auxiliary coatings while maintaining the properties of the surface treated by SPD methods. The technology of gas-dynamic coating includes heating the compressed gas (air), feeding it into the nozzle and forming a supersonic air stream in this nozzle, introducing a powder material into this stream, accelerating this material in the nozzle by a supersonic air flow and directing it to the surface of the workpiece. As a result, a special auxiliary coating is formed on the surface of the product, which provides optimal parameters of the SPD process.

Forming-Induced Residual Stress and Material Properties of Roll-Formed High-Strength Steels

Martensitic steels are widely used in the automotive lightweight application but less understood in aspects of post-forming material properties. The steels show good ductility in roll forming but occasionally experience delayed (hydrogen) fracture issues, which are believed to be due to the formation of localized residual stress and a reduced product of strength and elongation. To characterize the effect of roll forming process on the formation of residual stress and material properties variation of martensitic steel components, this paper investigates the forming-induced longitudinal residual stress and material property variation in a roll-formed high-strength MS1180 automotive rocker panel. The finite element analysis results for residual stress are validated by neutron diffraction measurements. The numerical model is used to analyze the full evolution of residual stress during the roll forming process and the effect on material properties with major focus on the product of strength and elongation. It is found that the flower design, in particular the overbending stages, play a significant role in the formation of residual stress and the change in material properties. The product of strength and elongation is significantly reduced across the profile, in particular in the corners. The achieved understanding will assist researchers comprehend the material properties of roll-formed component and therefore assist future studies aimed at preventing the occurrence of hydrogen fracture.

Selected Properties of the Surface Layer of C45 Steel Parts Subjected to Laser Cutting and Ball Burnishing.

In this article, we report the results of experimental studies on the impact of ball burnishing parameters on the roughness, microstructure and microhardness of the surface layer of laser-cut C45 steel parts. We also analysed the distribution of residual stresses generated in the surface layer of these parts. Laser-cut parts often require finishing to improve the quality of their surface. The tests performed in this study were aimed at assessing whether ball burnishing could be used as a finishing operation for parts of this type. Ball burnishing tests were performed on an FV-580a vertical machining centre using a mechanically controlled burnishing tool. The following parameters were varied during the ball burnishing tests: burnishing force Fn, path interval fw and the diameter of the burnishing ball dn. Ball burnishing of laser-cut C45 steel parts reduced the surface roughness parameters Sa and Sz by up to 60% in relation to the values obtained after laser cutting. Finish machining also led to the reorganization of the geometric structure of the surface, resulting in an increase in the absolute value of skewness Ssk. This was accompanied by an increment in microhardness (maximum microhardness increment was ΔHV = 95 HV0.05, and the thickness of the hardened layer was gh = 40 µm) and formation of compressive residual stresses in the surface layer.

Prediction of microstructural defects in additive manufacturing from powder bed quality using digital image correlation

Additive manufacturing (AM) of metal components offers tremendous promise to create complex parts with limited supervision. However, process quality and widespread acceptance are currently stymied by the formation of microstructural defects and residual stresses. In particular, lack-of-fusion (LoF) and keyhole defects frequently occur during AM production dependent on process conditions and can severely limit mechanical performance if not corrected. The effects of powder layer quality, where variations from the ideal have the potential to significantly alter defect formation, have not been thoroughly investigated in the literature. In this work, we employ a novel method incorporating in situ three-dimensional digital image correlation (3D-DIC) imaging of the powder bed in-process to identify and quantify the severity of powder bed irregularities during processing. Anomalies in the powder bed were detected, and their geometries quantified, layer by layer using the 3D-DIC analysis for parts produced at multiple energy density levels. Ex situ characterization via scanning electron microscopy identified the locations of physical defects for comparison to DIC data. The quantified powder bed 3D-DIC data, alongside ex situ identification of physical defect locations, was then fed into a Naïve-Bayes classification algorithm to predict the likelihood of physical defect formation based on the severity of in-process powder bed errors. This methodology has the potential to be used to predict physical defect formation based on detected powder spreading errors in-process, prior to the formation of many microstructural defects.

Finite element framework for electron beam melting process simulation

Electron beam melting (EBM®) is a metallic printing process that has become increasingly sophisticated over the past decade. The formation of residual stress due to a high-energy electron beam is considered a primary hindrance in the maturation of the process itself and, subsequently, the quality of the printed parts. Contrary to hit and trial, the finite element method (FEM) has become a prevalent technique for estimating residual stresses and subsequent distortion in additive manufacturing chunks. Since the EBM® is a powder bed fusion (PBF) process, powder material properties are substantially different from those of solid and undoubtedly important for efficient simulation. Several reviews have been published on FEM applications in additive manufacturing so far; however, a straightforward solution for material modeling from EBM® viewpoint is still needed. This critical review paper is an attempt to propose a material modeling approach to establish an adequate FEM model for EBM® process simulation.

Development of design methodology of technological process of ball-rod hardening with account for formation of compressive residual stresses

Introduction . The study results on the multicontact shock-vibrating machining using a ball-rod hardener are presented. Methods of surface plastic deformation processing, their advantages are described. The tool circuit diagram is given. Features, technological advantages, and the application area of the ball-rod hardening are specified. Materials and Methods . When conducting theoretical studies on the processing, factors, which affect the quality of the surface layer of the machined parts, were established. Dependences are given for calculating the surface roughness, the hardened layer depth, and the deformation ratio under ball-rod hardening. While studying the generation of residual stresses, the dependence for calculating the residual stresses generated in the surface layer of the machined part was specified. Results . The experimental findings of the processing requisite for verification of the adequacy of the theoretical models, as well as the routine of the experiments, are presented. A table and graphs clearly confirming good convergence of the theoretical and experimental data are given (the difference does not exceed 20%). Residual stresses in the surface layer are compressive which enables to predict high performance properties of the machined parts. The value of residual stresses on the workpiece surface is in the range of 130÷200 MPa. The depth of compressive residual stresses is in the range of 0.9-1 mm. The fatigue characteristic variation, the ultimate stresses of the cycle in depth, which affects the endurance limit, is calculated. It has been established that the processing of workpieces by a ball-rod hardener provides increasing the ultimate cycle stress under repeated loading by 27-35%. Discussions and Conclusions . The design methodology of technological process of ball-rod hardening can be used under the development of production at the machine-building enterprises. In accordance with the recommendations, the limits of the required quality parameters of the workpiece surface layer are set; the parameters of the ball-rod hardener, the interference fit and the radius of rod sharpening are selected. Quality parameters of the surface layer are calculated. Correction of the selected modes and re-calculation of the parameters of the machined surface are carried out until all the specified characteristics are located within the required limits.

Mechanical properties and pre-oxidation behavior of spark plasma sintered B4C ceramics using (Ti3SiC2+CeO2/La2O3) as sintering aid

B4C ceramic with the addition of 5 wt % (Ti3SiC2+ CeO2/La2O3) as sintering aids was fabricated by spark plasma sintering at a relatively low temperature of 1650 °C for 5 min at 80 MPa. The phase composition, microstructures, and comprehensive mechanical properties of the ceramics were studied in detail. The existence of reinforced second phase particles, the refinement of the matrix grains, the formation of residual stress along the grain boundaries and the appearance of the mixed fracture mode had a synergetic strengthening effect on the mechanical properties. The flexural strength, fracture toughness and Vickers hardness of B4C ceramics reached 565.2 ± 21.8/551.0 ± 25.2 MPa, 6.28 ± 0.01/6.41 ± 0.12 MPa·m0.5, and 28.51 ± 0.86/27.23 ± 1.08 GPa, respectively. In addition, to reduce the crack sensitivity of the ceramic, the ceramics were pre-oxidized at 800 °C for different durations. The flexural strength was increased by approximately 13.4% after the ceramic was oxidized at 800 °C for 45 min due to the crack-healing effect induced by the oxide glass B2O3 on the ceramic surface.

In situ studies of full-field residual stress mapping of SS304 stainless steel welds using DIC

Large tensile residual stress is detrimental to the structural integrity of welded structures. As a result, it is very important to understand the residual formation during the welding process. In this paper, a new non-contact welding residual stress measurement technique based on digital image correlation (DIC) is proposed as a way to investigate residual stress formation. To investigate the stress evolution of the welded plate, we conduct a series of experiments by using this new method. High-temperature full-field strain obtained from DIC was computed by incremental theory to acquire stress increment. Stress evolution and residual stress were obtained by superimposing the stress increment. Hole-drilling residual stress measurements for verification were also implemented. The maximum difference, which was 37 MPa between the two methods demonstrated that this new technique was able to characterize the full-field welding residual stress during the welding process.

Review on process model, structure-property relationship of composites and future needs in fused filament fabrication

This paper presents the state-of-the-art of additive manufacturing of composites for processing functional, load-bearing components. A general overview of different additive manufacturing methods is provided, and specific attention is focused on fused filament fabrication-based composites processing. Different process modeling strategies are summarized, and key aspects of these models are discussed. Significant results such as thermal and fluid flow characteristics, effects of nozzle geometry on melt flow, fiber orientation, bead spreading, and solidification, the formation of residual stresses, and deformation behavior are discussed from computational modeling perspective. The scientific advancement, model limitations, and future modeling needs are prescribed reviewing the current works. A general overview of material development in nano-micro-macro-scale reinforcement is also presented. Different length-scales of reinforcement has its own challenges and promises. The continuous fiber reinforcement has a great potential for being the next-generation composites manufacturing technology. However, the challenges in reducing the void content, better bonding between the fiber–matrix, and layer-layer adhesion, and process uncertainty are some of the key areas yet to advance. Based on the current limitations on computational modeling, materials development, and process modeling studies, future research needs and recommendations are provided.