Amount Of Residual Stress Research Articles

Numerical study of optimized processing condition in rolling strike ultrasonic nanocrystalline surface modification of copper

Ultrasonic nanocrystalline surface modification (UNSM) is state-of-art surface modification technique in which both the static and dynamic loads are contributed in work hardening of surface layer and amount of residual stress. The former performance causes microstructure refining while the later results to enhanced fatigue life. However, contribution of too many parameters in the process makes finding optimal parameter setting in which the process reaches to desired performance complex. In the present study, an attempt is made to find optimal combination of static force, tool tip diameter, tool tip material, linear velocity and vibration amplitude regarding the maximum plastic equivalent strain and the maximum affecting depth. The process is firstly modeled through finite element simulation in ABAQUS/EXPILICT software, and the results are further verified considering the residual stress distribution. Hereafter, a series of simulation runs are derived based on design of experiment to generate required data for optimization. In this stage, the run data are associated with response surface methodology to find optimal parameter setting regarding maximum PEEQ and maximum effective depth. The results showed that selection of 300 N static force, 9 mm tungsten carbide ball, 10 μm vibration amplitude and 1000 mm/min feed rate is optimum solution causes achieving maximum PEEQ of 3.44 at the depth of 200 μm. By finding optimal results, a series of USAT experiments have been carried out with optimum parameter setting and its hardness distribution, residual tress and microstructure has been compared with as received sample. It is found that the surface residual stress of the sample reaches from +40 MPa and reaches to –60 MPa after UNSM. On the other hand, the hardness of the sample enhances up to 50% after performing process under optimal setting.

Assessment of the distribution of residual mechanical stresses in plasma coatings

Purpose. To improve the performance of plasma coatings by searching for conditions for reducing the residual stresses. To achieve the goal, a method has been developed for determining residual stresses depending on the strength characteristics and the coating thickness.Research methods. Measurements of the mechanical properties of coatings during bending testing. Analysis of the measurement results of coatings strength.Results. A method is proposed for determining residual stresses by using the results of measurements of the mechanical characteristics of a plasma coating. The mechanical characteristics of the chromium-nickel powder coating during bending tests are investigated. A difference in the cohesive strength of the outer and inner layers of the coating was found. To calculate the residual stresses, we used the obtained values of the cohesive strength of the peeled coating and the bearing capacity of the coating adhered to the substrate. It is shown that for coating adhered to the substrate, the bearing capacity is less than the cohesive strength. The assumption that the residual stresses is determined by the difference between the cohesive strength and the bearing capacity of the coating is substantiated. The distribution of residual stresses across the plasma coating thickness and the residual stresses in the zone of contact with the substrate are found.Scientific novelty. It is shown that the cohesive strength exceeds the strength of the coating adhered to the substrate by the amount of residual stress. The distribution of residual stress and bearing capacity from changing coating thickness is found.Practical value. The results of measurements of cohesive strength and residual voltage make it possible to justify the reliability of the use of plasma coatings and analyze the data of strength measurements in order to determine the performance of parts.

Effect of Cut-Edge Residual Stress on Magnetic Properties in Non-Oriented Electrical Steel

The non-oriented electrical steels are widely used as motor core materials after the punching process. During the punching process, residual stress is inevitably generated at cut-edge; therefore, magnetic properties are deteriorated. In this paper, the effect of cut-edge residual stress on magnetic properties was investigated. The samples were cut by various methods to induce different amounts of residual stresses at cut-edges. The residual stress was analyzed by optical microscopy, micro Vickers hardness tester, and electron backscatter diffraction. The magnetic properties in low-field strength were closely related to residual stress, because the magnetic domain wall motion is inhibited by crystal lattice defects.

Finite element modeling to predict the steady-state structural behavior of 4D textiles

Four dimensional (4D) textiles consist of a textile with a printed polymeric grid, where deformation of the grid is induced by introducing residual stresses in the textile, in this case through pre-stretching of the textile substrate prior to printing. The fourth dimension refers to the ability of the structure to change shape over time by changing the residual stress in the textile. In order to design a useful component for a specific application, the material properties of constituents, direction and amount of residual stress, anisotropy of the textile substrate, geometry of the printed polymer, and pattern of the printed grid can all be altered. Due to the large amount of design variables involved, a validated modeling technique that can account for the complex material behavior of the soft, flexible textile under large strains and deformations along with the bifurcation and stability behavior of buckling beams is needed. In this study, an initial model was created to capture the time-independent buckling behavior and compared with experiments for rectangular elements of varying geometry and pre-strain. Once the model was calibrated, it fit experiments well, although additional advancements must be made to predict the nonlinear behavior of a wide variety of architectures with further accuracy. Finally, modeling strategies for large grids are laid out and discussed, and preliminary results are shown. Although this model did not include the transient nature of shape change, it can serve as a precursor for designing 4D Textiles and eventually predicting their time-dependent behavior under loading changes.

Relation between residual stresses and microstructure evolution in Al–Si alloys based on different casting parameters

ABSTRACTMost designers take into consideration the stresses that act on a material but despite safety considerations, failure may occur due to other factors that were neglected in their design. These factors can be a pre-existing flaw, microstructure deficiency or the presence of residual stresses. Depending on the stress type, residual stresses combined with applied stresses can aid or hinder failures. Consequently, reducing the amount of residual stress can have a promising effect on the life of the component. Different casting parameters can change the microstructure and residual stresses of castings. In this research, the relation between residual stresses and microstructure evolution under the influence of different casting parameters was investigated, using both Al–Si–Mg (Al-356) and Al–Si–Mg–Cu (Al-319) alloys. Solidification rate, quenching rate, aging temperature and aging time were the main parameters considered for this study. The results indicate that the magnitude of the residual stresses increases with increasing solidification rate and quenching rate. Also, the residual stress relieving is proportional to the aging temperature

Residual Stress–Based Fatigue Design of Welded Structures

Abstract Fatigue design concepts for welded structures generally consider residual stresses as a factor affecting the mean stress influence. Residual stresses are mostly interpreted as mean stresses. In addition, high tensile residual stresses are conservatively assumed, resulting in maximum effective load stresses from fatigue loading in the order of the yield strength. The consequence of this is that additional static load stresses may have no influence on the resulting fatigue strength because the local effective mean stress (residual stresses and load mean stresses) is always high. The related evaluation concepts neither distinguish between different steel grades nor between different origins and amounts of possible residual stresses in welded joints. The real magnitude of existing residual stresses is also usually not considered, because in practice, usually no explicit knowledge of the residual stresses at critical sites of a construction is available because residual stress measurements are not state of the art in welding practice. For an explicit consideration of residual stresses in design concepts, the sign, the initial amount, and especially the amount of the residual stresses after a load induced relaxation must be considered. Therefore, the steel grade and the condition of the material are of great importance, as well as the local stress condition influenced by welding-induced notch geometry. The article shall give an overview about the state of the art of consideration of residual stresses in fatigue design concepts for welded structures and the background of their development. Finally, a new approach shall offer a possibility for an enhanced consideration of residual stresses in design concepts based on the explicit knowledge about the effective residual stresses that can actually be observed with different measurement concepts.

The Influence of Plastic Deformation on the Low-Cycle Fatigue During the Burnishing of Holes in Flat Specimens of D16chT Steel

The paper deals with one of the most important problems of such closely related industries as mechanical engineering and aircraft manufacturing, involving the determination of the service life of components and structures operating under cyclic loading conditions. The presence of local structural and manufacturing stress concentrators greatly complicates the determination of the predicted life of components and structures at their design stage. The burnishing technique, namely, the method of plastic deformation of walls of the hole, aimed at achieving the amount of the residual plastic strain on their surface, is used to strengthen components with holes. The results of low-cycle fatigue tests conducted in repeating tension are presented for flat laboratory specimens of an aircraft aluminum alloy D16chT with a central cylindrical manufacturing hole hardened by burnishing. The burnisher geometry that ensures the required value of the residual plastic strain level (1, 2, and 3%) on the hole surface is calculated. The cyclic tensile loading of specimens at the stresses in a pulsating load cycle was performed in the range of 150 to 270 MPa at a frequency of 3 Hz using the equipment Bi-02-112. The influence of the amount of plastic strain in the burnished hole of the specimen on its cyclic life and fracture as a function of the load value is observed. It is found that due to plastic strain hardening of the surface of manufacturing holes, a local area of compressive residual stresses occur, causing the stress concentration around the manufacturing hole to decrease and the level of limit loads to increase. It is shown that the specimen, having a manufacturing hole hardened by burnishing (up to a plastic strain of 3%) and being cyclically loaded by a tensile stress to 170 MPa, failed not at the hole (the stress concentrator). Both the onset of the microcrack initiation and its further propagation take place in a solid region of the specimen. This is indicative that with a certain amount of residual stresses in the burnished hole, the specimen fracture under low-cycle fatigue becomes insensitive to the presence of this concentrator.

Evaluation of surface integrity of WEDM processed inconel 718 for jet engine application

A unique superalloy, Inconel 718 has been serving for aerospace industries since last two decades. Due to its attractive properties such as high strength at elevated temperature, improved corrosion and oxidation resistance, it is widely employed in the manufacturing of jet engine components. These components require complex shape without affecting the parent material properties. Traditional machining methods seem to be ineffective to fulfil the demand of aircraft industries. Therefore, an advanced feature of wire electrical discharge machining (WEDM) has been utilized to improve the surface features of the jet engine components. With the help of trim-offset technology, it became possible to achieve considerable amount of residual stresses, lower peak to valley height, reduced density of craters and micro globules, minimum hardness alteration and negligible recast layer formation.

FEM prediction of welding residual stresses in fibre laser-welded AA 2024-T3 and comparison with experimental measurement

Welding generates a considerable amount of residual stresses which affect the structural integrity of welded components. It is often assumed that the magnitude of residual stresses around the welded joint is as high as the yield stress of the material. In this investigation, such assumption was found to be overly conservative and failed to accurately represent the distribution of residual stresses in fibre laser-welded aluminium alloy 2024-T3 sheets. Welding simulation based on the finite element method was used to reliably determine the distribution and magnitude of transient residual stress fields and distortions in thin sheets welded using three different sets of welding parameters. The accuracy of the finite element models was checked by calibrating with experimentally measured weld pool geometries and temperature field prior to conducting parametric studies. X-ray and neutron diffraction measurements were performed on the surface and in the bulk of the welded components, respectively, and compared with numerical results. The influence of weld metal softening, welding parameters and restraints on residual stresses and distortion were investigated systematically by numerically simulating ideal conditions which eliminate the practical limitations of conducting experimental studies, for process optimization as well as evaluation of in-service structure integrity and failure modes of the welded sheets.

Microstructure and mechanical properties of Inconel 718 produced by selective laser melting: Sample orientation dependence and effects of post heat treatments

Inconel 718 produced by selective laser melting (SLM) has been characterized with focus on the microstructure, the dependence of sample orientation on the mechanical properties and the effects of post heat treatments. The as-manufactured IN718 has a very fine cellular-dendritic structure with fine Laves phases precipitating in the interdendritic region, and electron backscatter diffraction (EBSD) analysis shows that both the vertically and horizontally built samples have relatively weak texture. The vertically built samples show lower tensile strength but higher ductility than the horizontally built samples, and the mechanism is shown to be partly due to the crystallographic feature but more importantly due to the different amount of residual stress and dislocations accumulated in these two kinds of samples. Applying heat treatments can significantly increase the strength while decrease the ductility correspondingly, and difference in yield strength between the vertically and horizontally built samples decreases with increasing the heat treatment temperatures, mainly due to the removal of residual stress and dislocations.

Stress-induced birefringence control in femtosecond laser glass welding

Glass welding by femtosecond laser pulses causes microscopic structural modifications, affecting the refractive index due to residual stress. Locally induced birefringence is studied by photoelasticimetry using a polarized light microscope. The study is performed on borosilicate thin glass plates using an industrial femtosecond laser generating 300 fs pulses at 500 kHz, with a 100 mm focusing length F-theta lens allowing fast welding. For low-energy deposition, the principal birefringence axes are determined to be homogenous along the seam and perpendicular and parallel to the laser scanning direction. Tensile stress is induced in the laser scanning direction by the welding seams. The induced birefringence is determined to be equivalent for in-volume irradiated track and welding seams. An inhomogeneity of the birefringence within the seam is observed for the first time at high-energy deposition. The distribution of the birefringence can be controlled with the laser scanning patterns. The amount of residual stress is measured by compensating the local birefringence. The birefringence $$\Delta ~n$$ is estimated at $$2.4~\times ~10^{-4}$$ , corresponding to a residual stress amount around 59 MPa. The influence of the welding geometry is also illustrated.

Study the Effect of Multilayer Single Point Incremental Forming on Residual Stresses for Bottom Plates

Abstract
 
 Knowing the amount of residual stresses and find technological solutions to minimize and control them during the production operation are an important task because great levels of deformation which occurs in single point incremental forming (SPIF), this induce highly non-uniform residual stresses. In this papera propose of a method for multilayer single point incremental forming with change in thickness of the top plate (0.5, 0.7, 0.9) mm and lubrication or material between two plates(polymer, grease, grease with graphite, mos2) to knowing an effect of this method and parameters on residual stresses for the bottom plates. Also compare these results for the bottom plates with the single plate at same thickness 0.9 mm.The results showed that when increase thickness of the top plate the value of residual stresses will decrease for bottom plates and when used graphite with grease between two plates gives less residual stresses (R.S = 60.173 MPa.) reverse when used Mos2 which will gives a larger residual stresses (R.S = 146.617 MPa.) in the bottom plate.
 Keywords: Multilayer Single Point Incremental Forming (SPIF), Residual Stresses, Lubrication.

Local Scale Microstructural Effects from the Deformation and Recrystallization of Non-Oriented Electrical Steels

The magnetic properties of non-oriented electrical steels are determined by a combination of several metallurgical variables, including crystal orientation, misorientation (the orientation difference between two crystal orientations), and the amount of residual stress associated with plastic deformation. These variables are influenced by cold rolling and annealing. In order to study these relationships, samples in the semi-processed condition were subjected to an additional cold roll and a subsequent annealing at different temperatures, and then characterized using electron backscatter diffraction and nanoindentation. The process routing for these samples was not intended to be representative of real-world manufacturing; the purpose was to produce a spread in the metallurgical variables being investigated. Although some trends were observed involving orientation and misorientation, when present, deformation observed close to grain boundaries appeared to be the most influential variable on the magnetic properties.

Experimental study of produced thermal stresses in thin arc welded plates: application of constructal theory in welding paths

In the present investigation, the basics of constructal theory are used to suggest new welding paths in order to have better heat distributions which will reduce residual stresses in weldments. Aluminum plates have been experimentally welded with a GTA welding instrument. The produced thermal stresses in weldments are measured by X-ray diffraction (XRD) method. Doing so, the experiments are qualitative measurements of residual stresses at different points of weldments. The analysis is based on the comparison of the produced residual stresses in different welding models which have received a fixed amount of heat input during welding. In order to have a tool for further comparison, a numerical modeling is also developed which proved that the shape of experimental residual stress distribution has a good agreement with the results of the presented numerical simulation. A reference point, through which an almost equal amount of input heat is passing, is considered to make the comparison between different models more meaningful. Finally, the amount of residual stress at various points, in different welding models, showed that the suggested constructal welding paths resulted in less residual stresses in weldments. Furthermore, the effect of welding sequences in the amount of generated residual stresses confirmed the previous investigations.

Effect of Cooling Medium on Solution Treatment Response of Titanium Alloy Ti-5Al-5V-2Mo

Titanium alloys are widely used in aerospace industry in the areas of pressure vessels, airframe structures, landing gears, aeroengine compressor blades etc. The principal qualities of titanium alloys required for these applications are high specific strength, low density and high specific modulus. Among the families of Ti alloys, high strength titanium alloys come under martensitic α + β and metastable β alloys. Titanium alloy Ti-5Al-5V-2Mo (BT-23) is an important example of martensitic α + β alloy similar to the work horse Ti6Al4V alloy which exhibits good combination of strength and ductility in solution treated and aged conditions. But due to quenching from solution treatment temperature, the alloy tends to retain good amount of residual stresses. The severity of residual stress increases with increase in solution treatment temperature as well as severity of quench. An attempt has been made to study the effect of air cooling subsequent to solution treatment to compare the strength of the alloy vis-à-vis that achievable during water quenching. An attempt has also been made to correlate the microstructure evolution, hardness with variation in solution treatment temperature and quench severity in titanium alloy Ti-5Al-2Mo-5V. Samples subjected to air cooling subsequent to solution treatment exhibited higher microhardness when compared to water quenched samples. It is proposed that dynamic aging and/ or stress relieving occurs during air cooling from solution treatment temperature down to room temperature. Also the fine α precipitates formed during air cooling may be resulting in higher hardness compared to the α’’/α’ formed during water quenching. The same has been supported by thermal analysis of air cooling and water quenching processes employed subsequent to solution treatment.

A parametric study of laser spot size and coverage on the laser shock peening induced residual stress in thin aluminium samples

Laser Shock Peening is a fatigue enhancement treatment using laser energy to induce compressive Residual Stresses (RS) in the outer layers of metallic components. This work describes the variations of introduced RS-field with peen size and coverage for thin metal samples treated with under-water-LSP. The specimens under investigation were of aluminium alloy AA2024-T351, AA2139-T3, AA7050-T76 and AA7075-T6, with thickness 1.9 mm. The RS were measured by using Hole Drilling with Electronic Speckle Pattern Interferometry and X-ray Diffraction. Of particular interest are the effects of the above mentioned parameters on the zero-depth value, which gives indication of the amount of RS through the thickness, and on the value of the surface compressive stresses, which indicates the magnitude of induced stresses. A 2D-axisymmetrical Finite Element model was created for a preliminary estimation of the stress field trend. From experimental results, correlated with numerical and analytical analysis, the following conclusions can be drawn: increasing the spot size the zero-depth value increases with no significant change of the maximum compressive stress; the increase of coverage leads to significant increase of the compressive stress; thin samples of Al-alloy with low Hugoniot Elastic Limit (HEL) reveal deeper compression field than alloy with higher HEL value.

Hydrothermally grown boron-doped ZnO nanorods for various applications: Structural, optical, and electrical properties

The structural, optical, and electrical properties of ZnO and BZO nanorods were investigated using fieldemission scanning electron microscopy, x-ray diffraction (XRD), photoluminescence (PL), and van der Pauw Hall-effect measurements. All the nanorods had grown well on the ZnO seed layers and were hexagonal. The BZO nanorods were shorter than the undoped ZnO nanorods, and the BZO nanorods grew shorter with increasing concentration of B to 2.0 at. % while the average length of the nanorods doped with 2.5 at. % B increased from 1620 to 1830 nm. The XRD patterns suggest that the amount of residual stress in the nanorods decreased with increasing concentration of B in the nanorods. The PL spectra showed near-bandedge and deep-level emissions, and B doping also varied the PL properties of the ZnO nanorods. The Halleffect data suggest that B doping also varied the electrical properties such as the carrier concentration, mobility, and resistivity of the ZnO nanorods.

Modeling of Cure-Induced Residual Stresses in 3D Woven Composites of Different Reinforcement Architectures

This paper presents finite element modeling effort to predict possible microcracking of the matrix in 3D woven composites during curing. Three different reinforcement architectures are considered: a ply-to-ply weave, a one-by-one and a two-by-two orthogonal through-thickness reinforcement. To realistically reproduce the as-woven geometry of the fabric, the data from the Digital Fabric Mechanics Analyzer software is used as input for finite element modeling. The curing processed is modeled in a simplified way as a uniform drop in temperature from the resin curing to room temperature. The simulations show that the amount of residual stress is strongly influenced by the presence of through-thickness reinforcement.

Effect of feed and roller contact start point on strain and residual stress distribution in dome forming of steel tube by spinning at an elevated temperature

Tube spinning, without mandrel, is a common process used for manufacturing pressure vessels, e.g. CNG (Compressed Natural Gas) capsules for automotive industry and fire extinguishers. The process is carried out at an elevated temperature for forming a dome on thick wall steel tube ends. Two of the most important control parameters in the process are the “roller contact start point” (RCSP) and spinning feed (pitch), both of them highly affecting the process time and deformation behavior of the tubes and therefore success and quality of the product. In this article, using a three-dimensional dynamic explicit finite element model, the effects of these parameters are investigated on circumferential, axial and radial (thickness) strains of the formed tube in three thickness layers of the tube wall. The model is also verified by experiment. While circumferential strain is shown to be independent of the feed, axial and thickness strains are highly affected by both the feed and roller contact start point. It is shown that when the roller contact start point distance from the free end of the tube increases, there is a risk of indentation instead of normal bending behavior. It is also shown that axial strain has an inverse relation with feed, i.e. decreasing the feed results in further elongation of the tube. On the other hand, thickness strain increases by increasing the feed, so bigger thicknesses are expected in domes manufactured by higher feeds. In addition, it is shown that increasing the feed results in a decrease of the equivalent strain. The amount of residual stress (regardless of the temperature change) increases with increasing feed and its distribution is more uniform for higher distances of the contact start point from the free end.

A New Experimental Method for the Introduction of a Predetermined Amount of Residual Stresses in Fatigue Test Specimens

A new experimental method for the incorporation of residual stresses (RS) in standard fatigue steels specimens was developed. RS were introduced by means of high frequency (360 kHz) induction heating. Surface tensile RS resulted from cooling down the specimen subjected to a high thermal gradient. To preserve the mechanical properties of the steel, it was necessary to circulate a coolant at the center of the specimen. The 304L austenitic stainless steel does not undergo phase transformation nor micro structural changes in the solid state and was thus selected for this purpose. Multiphysics finite element (FE) analysis was used to calculate the distributed RS in the fatigue samples. These calculations were compared to XRD measurements and a very good agreement was obtained. It was therefore demonstrated that RS induced with induction heating could be numerically assessed. This conditioning method was then proved efficient to study the only influence of a predetermined amount of RS on the fatigue properties of austenitic 304L steel without undergoing influences of other parameters such as microstructure, surface finish and geometry.