Introduction Of Residual Stresses Research Articles

Influence of Vertical Straightener Roller Shape on Residual Stress Level in Railway Rails

The required rail straightness is achieved by straightening with roller straighteners. The consequence of the straightening operation is the introduction of residual stresses to the straightened rail. An excessive level of residual stresses accumulated in the rail during use in the track may lead to its damage or fracture. ArcelorMittal Poland S.A., in cooperation with Łukasiewicz Research Network – Institute for Ferrous Metallurgy, carried out a research project (POI R.01.02.00-00-0167/16) the aim of which was to reduce residual stresses in railway rails by changing the technological parameters of the straightening process. The results of the presented study relate to rails 60E1 and 60E2. The study includes the measurement, testing, calculations and analyses of the obtained results. The conducted research indicates the possibility of obtaining a low level of residual stress in the rails for a system consisting of a 7-roller vertical straightener and a 9-roller horizontal straightener by changing the roller settings, the shape of the rollers, the shape of the rail foot and its curvature.

Consistent memory surface model for plateau and hardening regions

Mild steels are frequently used in building structures because of their high strength, productivity, processability, and weldability. One key feature of mild steels is their yield plateau, which is followed by a hardening region in the stress–strain relationship. During large earthquakes, building members can experience a large plastic strain whose amplitude is difficult to predict beforehand. Constitutive equations applicable to the full-range strain field are necessary for accurate structural safety evaluation. This study provides novel constitutive equations for the plateau region, capable of reproducing a yield plateau. A set of hardening constants was proposed to satisfy the consistency condition of the plastic multiplier under any loading pattern. The closed form of the stress–strain relationship was derived to calibrate the material constants. The material constants were calibrated using two types of material test results. The results of the proposed model were consistent with the material test results under cyclic loading at various strain amplitudes. This was validated by comparing the shear buckling and lateral torsional buckling test results of an H-shaped beam with the finite element analysis (FEA) results. The numerical demonstration also highlighted the significance of not only material constitutive laws but also the introduction of residual stress and initial imperfections in reproducing the pre- and post-buckling behaviors. The convergence of the residual force for the proposed model was equivalent to those of the authors’ previous model and the Chaboche model. These results indicate that the proposed model can predict hardening phenomena at the material and structural levels in the plateau and hardening regions.

Effect of heat treatment on microstructure and mechanical properties for laser powder bed fusion of nickel-based superalloy: A review

Laser powder bed fusion (LPBF) is most widely used method for presenting an innovative manufacturing approach that operates layer by layer. This technique relies on a geometrical model and offers a viable substitute for material processing. The utilization of LPBF for producing nickel alloys has garnered significant interest across various domains due to their exceptional attributes. These attributes include excellent corrosion resistance, favorable mechanical properties, and the quality of the manufactured alloys. The particular solidification conditions arising from the metal fusion in the selective laser fusion process, combined with layer-by-layer deposition, give rise to unique microstructural characteristics. These include the development of supersaturated solid solutions, significant microstructural refinement, and the introduction of residual stresses. As a result, adjustments might be necessary for heat treatment and hot isostatic pressing, practices commonly employed with conventionally manufactured nickel alloys. These adaptations would accommodate the metallurgical nuances specific to Ni alloys produced through direct metal laser deposition, effectively addressing issues arising from the inherent characteristics of the process. This review paper compiles the most recent scientific discoveries concerning thermal treatment applied to additively manufactured nickel alloys using the selective laser sintering process.

Improved adhesion of cathodic arc PVD AlCrSiN coating on ion-implanted WC-Co substrates

Ion implantation has been shown to improve adhesion strength of AlCrSiN coatings due to a synergic enhancement on fracture toughness and load bearing capability of the substrate that can potentially increase the in-service efficiency of coated cutting tools. In this work, AlCrSiN coatings deposited by PVD on WC-Co substrates implanted with Ti, Cr and N ion species have been processed. The mechanical properties and adhesion have been characterized by contact techniques and the residual stress of the coatings and substrates have been evaluated using FIB-DIC technique and Vickers indentation tests, respectively. An improvement of adhesion strength is obtained for treated substrates, especially for those implanted with titanium and chromium ions. This improvement is attributed to the introduction of residual stresses in the substrate, which increases its fracture toughness and enhances its load bearing capability.

Numerical Simulation on Laser Shock Peening of B4C-TiB2 Composite Ceramics.

The introduction of residual stresses using laser shock peening (LSP) is an effective means of improving the mechanical properties of ceramics. Numerical simulations offer greater convenience and efficiency than in-lab experiments when testing the effects of different processing techniques on residual stress distribution. In this work, a B4C-TiB2 ceramic model based on the extended Drucker-Prager model was established to investigate the effects of laser power density, the number of impacts and laser spot overlapping rate on the residual stress distribution, and the reliability of the simulation method was verified by experimental data. The following results are obtained: increasing the laser power density and the number of impacts can increase the surface residual compressive stress and reduce the depth of the residual compressive stress; the presence of multiple impacts will significantly reduce the depth of the residual compressive stress layer; with the increase in the laser spot overlapping rate, the compressive residual stress in the processed area gradually increases and is more uniformly distributed; the best processing effect can be achieved by using a spot overlapping rate of 50%.

Investigation on Residual Compressive Distribution of High-Strength Steel for Bridges by Base Metal Hammer Impact Peening

Various peening techniques have been used to improve the fatigue strength of steel structures. Among them, base metal impact hammer peening shows significant improvement in fatigue strength in ordinary steel, but the effect on high-strength steel has not been sufficiently studied. Accordingly, this study applied base material hammer impact peening to test specimens of 780 MPa grade high-strength steel (HT780) and 490 MPa grade ordinary steel (SM490), and the residual stress was measured and simulated. The experimental results clarified that a large compressive residual stress was introduced into the inner part of the plate thickness near the indentation in the high-strength steel, although the range of introduction of residual stress was equivalent in both the ordinary steel and high-strength steel.

Galvanic Corrosion of Copper/Carbon Steel Couples Under Simulated Disposal Conditions for Used Nuclear Fuel

Deep geological containment of used nuclear fuel in Canada will rely on both engineered and natural barriers. The engineered barrier system consists of copper-coated used fuel containers and the compacted bentonite clay buffer boxes in which the containers will rest. This work focuses on a possible degradation mode known as galvanic corrosion, between the Cu coating and the carbon steel (CS) substrate of the container, which may occur at a hypothetical through-coating defect. Corrosion of the Cu/CS couple was studied in the presence of various amounts of chloride, bentonite, and oxygen, using electrochemical tests complemented by surface characterization and 3D X-ray imaging. Cu-coated CS specimens with small holes drilled through the coatings (to simulate defects) were galvanically corroded, and corrosion potential and linear polarization resistance measurements, coupled with in situ X-ray micro-computed tomography and post-mortem Raman spectroscopy and scanning electron microscopy/energy dispersive X-ray analysis, were used to evaluate the nature and extent of CS corrosion.In the absence of bentonite, the CS demonstrated the ability to form a protective oxide barrier. Formation of a protective film was associated with higher polarization resistance values, though the linear increase in corrosion volume over time suggests that the protection was not effective, and asymmetric growth of the corroded volume suggests that the film coverage was not uniform. The oxide layer, when cross-sectioned and viewed by scanning electron microscopy, was observed to be thick but porous, and composed largely of lepidocrocite (γ-FeO(OH)).In the presence of bentonite, the very negative corrosion potential and high polarization resistance values observed suggest that the bentonite was acting as a barrier to O2 diffusion to both the Cu and the CS surfaces. Such benign conditions were also reflected in the X-ray micro-computed tomography analysis, which showed minimal corrosion damage and >80% reduction in corrosion rates over bentonite-free conditions. The bentonite also acted as a barrier to transport of aqueous ferric and ferrous species, which allowed the formation of solid corrosion products on the CS at the base of the hole by preventing their upward transport and deposition atop the Cu coating.The results also provide a comparison of the corrosion susceptibility of the Cu/CS interfaces created by cold spray and electrodeposition techniques. In all cases, the Cu/CS interface was more susceptible to corrosion than the bulk CS, due to residual stress and plastic deformation induced by CS surface modification before or during coating application. The lower adhesion of cold-sprayed coatings made the Cu/CS interface of cold-sprayed specimens slightly more susceptible to corrosion than that of electrodeposited samples. The progression of corrosion at an artificial defect in cold spray Cu-coated CS observed by X-ray micro-computed tomography is shown in Figure 1 as an example. In cold-sprayed specimens, interfacial corrosion occurred symmetrically around the drilled hole and corrosion propagated preferentially around Cu splats at the Cu/CS interface. The machining grooves at the interface of electrodeposited specimens caused some preference for interfacial corrosion parallel to those lines, due to introduction of residual stress from plastic deformation. When interfacial corrosion was less extensive, as in the presence of bentonite, corrosion occurred symmetrically around the hole in both electrodeposited and cold-sprayed specimens.These experiments also demonstrated the effectiveness of bentonite slurry in suppressing galvanic corrosion in the Cu/CS couple by creating benign corrosion conditions in the through-coating defect. Figure 2 shows the suppression of corrosion rates by the presence of bentonite.This work provides insight into the conditions which may exacerbate or mitigate galvanic corrosion in the deep geological repository, contributing to the body of research which will support prediction of the long-term performance of the engineered barrier system. Figure 1

Impact of residual stress evoked by pyramidal embossing on the magnetic material properties of non-oriented electrical steel

Targeted magnetic flux guidance in the rotor cross section of rotational electrical machines is crucial for the machine’s efficiency. Cutouts in the electrical steel sheets are integrated in the rotor sheets for magnetic flux guidance. These cutouts create thin structures in the rotor sheets which limit the maximum achievable rotational speed under centrifugal forces and the maximum energy density of the rotating electrical machine. In this paper, embossing-induced residual stress, employing the magneto-mechanical Villari effect, is studied as an innovative and alternative flux barrier design with negligible mechanical material deterioration. The overall objective is to replace cutouts by embossings, increasing the mechanical strength of the rotor. The identification of suitable embossing geometries, distributions and methodologies for the local introduction of residual stress is a major challenge. This paper examines finely distributed pyramidal embossings and their effect on the magnetic material behavior. The study is based on simulation and measurements of specimen with a single line of twenty embossing points performed with different punch forces. The magnetic material behavior is analyzed using neutron grating interferometry and a single sheet tester. Numerical examinations using finite element analysis and microhardness measurements provide a more detailed understanding of the interaction of residual stress distribution and magnetic material properties. The results reveal that residual stress induced by embossing affects magnetic material properties. Process parameters can be applied to adjust the magnetic material deterioration and the effect of magnetic flux guidance.

Finite Element Simulation of Residual Stress Determination Based on Spherical Indentation Accumulation Morphology

The introduction of residual stress during the processing of materials has an important impact on the properties of the materials, so it is important to accurately measure the residual stress of the material. This paper established a finite element model of spherical indentation under the action of non-equivalent biaxial residual stress. Then we extracted the full-field accumulation state near the indentation under different stress states from the simulation results and summarized the pile height distribution near the indentation under different stress states. From the simulation, we found that the maximum pile-up height near the indentation point presented a regular trend.

Recent advantages in laser fabrication of micro‐channel heat exchangers

Micro‐channel heat exchangers transfer more heat because of having a greater surface area compared to the conventional generation. This principle advantage can be applied widely in various industries for waste heat recovery purposes. Laser micromachining is a unique fabrication process, which presents some challenges. The main drawback of laser processes is introduction of residual stresses, which create distortion on the surface of heat‐affected areas. This study investigates some recent improvement in the fabrication methods of micro‐channel heat exchangers and concludes the strategies to control the distortion.

Investigation on femto-second laser irradiation assisted shock peening of medium carbon (0.4% C) steel

In the present study, the effect of femtosecond laser irradiation on the peening behavior of 0.4% C steel has been evaluated. Laser irradiation has been conducted with a 100μJ and 300fs laser with multiple pulses under varied energy. Followed by laser irradiation, a detailed characterization of the processed zone was undertaken by scanning electron microscopy, and X-ray diffraction technique. Finally, the residual stress distribution, microhardness and wear resistance properties of the processed zone were also evaluated. Laser processing leads to shock peening associated with plasma formation and its expansion, formation of martensite and ferrito–pearlitic phase in the microstructure. Due to laser processing, there is introduction of residual stress on the surface which varies from high tensile (140MPa) to compressive (−335MPa) as compared to 152MPa of the substrate. There is a significant increase in microhardness to 350–500VHN as compared to 250VHN of substrate. The fretting wear behavior against hardened steel ball shows a significant reduction in wear depth due to laser processing. Finally, a conclusion of the mechanism of wear has been established.

Application of Vibropeening on Aero – Engine Component

The ball pressure polishing or Vibropeening method is one of famous polishing methods mainly used for treatment of car wheels or various types of furniture and cutlery. Together with the surfaces improvement without material removal as an optical embellishment this method enables hardening of component surfaces due to introduction of residual stresses by the “knock” effect of the media vibration. The hardening effect has not been studied in detail so far.Vibropeening could be used on aero-engine components as an alternative technology to shot peening and vibropolishing, which allows reduction of cost especially on complex geometry parts such as blisk.This paper describes the treatment of test components for understanding of key process variables and the method applied for process evaluation. Special attention was paid on investigating the correlation of process parameters and surface properties of compressor blades.Variation of process variables in vibropeening achieved a significant increase of residual stress level - comparable with shot peening - on compressor blades.

Evaluation of the Impact of Residual Stresses in Crack Initiation with the Application of the Crack Compliance Method Part I, Numerical Analysis

The understanding of how materials fail is still today a fundamental research problem for scientist and engineers. The main concern is the assessment of the necessary conditions to propagate a crack that will eventually lead to failure. Nevertheless, this kind of analysis tends to be more complicated, when a prior history in the material is taken into consideration and it will be extremely important to recognize all the factors involved in this process. In this work, a numerical simulation of the introduction of residual stresses, which change the crack initiation conditions, in a modified compact tensile specimen to change the condition of crack initiation is presented. Four numerical analyses were carried out; an initial evaluation was performed in a specimen without a crack and it was used for the estimation of a residual stress field produced by an overload; three more cases were simulated and a crack was introduced in each specimen (1 mm, 5 mm and 10 mm, respectively). The overload was then applied to set up a residual stress field into the component; furthermore, in each case the crack compliance method (CCM) was applied to measure the induced residual stress field. By performing this numerical simulation, the accuracy of the crack compliance method can be evaluated. On the other hand, elastic-plastic finite element analysis was utilized for the residual stress estimation. The numerical analysis was based on the mechanical properties of a biocompatible material (AISI 316L). The obtained results provided significant data about diverse factors, like; the manner in which a residual stress field could modify the crack initiation conditions, the convenient set up for induction of a beneficial residual stresses field, as well as useful information that can be applied for the experimental implementation of this research.

Assessment of the Crack Compliance Method and the Introduction of Residual Stresses by Shot Peening Using the Finite Element Method

The interest on the application of the shot peening process to arrest and/or delay crack growth is rising. The main effect of the shot peening technique is to introduce a residual stress field that increases the working life of mechanical components. In this paper, it is presented the numerical simulation (FEM) of the shot peening process and the effect of introducing a residual stress field. Besides, the consequence of changing the sizes of the impacting ball is analyzed. This work also used the Crack Compliance Method (CCM) for the determination of residual stresses in beams subjected to a numerical simulation of a shot peening process. The numerical results obtained provide a quantitative demonstration of the effect of shot peening on the introduction of residual stresses by using different sizes of impacting balls and assess the efficiency of the CCM.

Fatigue crack growth through a residual stress field introduced by plastic beam bending

ABSTRACTWe present predictions and measurements of fatigue crack growth rates in plastically bent aluminium 2024‐T351 beams. Beam bending and fatigue were carefully controlled to minimize factors other than residual stress that could affect the fatigue crack growth rate, such as large plastic strains or residual stress relaxation. The residual stress introduced by bending was characterized by a bending method and by the slitting method, with excellent agreement between the two methods. Crack growth rates were predicted by three linear elastic fracture mechanics (LEFM) superposition based methods and compared to experimental measurements. The prediction that included the effects of partial crack closure correlated with experimental data to within the variability normally observed in fatigue crack growth rate testing of nominally residual stress free material. Therefore, we conclude that crack growth through residual stress fields may be predicted using the concept of superposition as accurately as crack growth through residual stress free material, provided that the residual stress is accurately known, the residual stress remains stable during fatigue, the material properties are not changed by the introduction of residual stress, and that the effect, if any, of partial crack closure is taken into account.

Effect of strain hardening on residual stress distribution in beams determined using the crack compliance method

This work used the crack compliance method for the determination of residual stresses in beams subjected to prior straining before the introduction of residual stresses through bending. The paper also introduces a support system that allows free movement of specimens during cutting by electric discharge machining. The experimental testing and verification procedure considered factors such as different materials and strain hardening levels. The results obtained provide a quantitative demonstration of the effect of prior strain hardening on residual stress distribution in beams.

The modelling of residual stresses due to surface peening using eigenstrain distributions

The beneficial effect of surface peening (including shot peening, laser shock peening, low plasticity burnishing, etc.) on fatigue resistance of structural alloys is well documented and widely used in industry to improve component life. It is perhaps the most widely used technique that relies on the introduction of residual stresses into the component by direct mechanical means. The resulting stress states are usually evaluated experimentally by X-ray diffraction or other stress measurement techniques. In order for shot peening operations to be effective and reliable, the process of introducing residual stresses and strains into peened components must not only be controlled but also be predictable and quantifiable. The present paper establishes a framework for predictive modelling of the residual stress states due to surface peening. Firstly, uniform (within planes parallel to the surface) plastic deformation of the surface layer taking place during shot peening of a thin plate is simulated using the concept of eigenstrain. As a further demonstration of the capabilities of the proposed approach, flexible plate theory is applied to the analysis of stresses and deformations arising due to local peening within a circular area. The results are of considerable use and significance for the analysis of shot peening and peen forming operations.

3D Photoelasticity And Numerical AnalysisOf A Cylinder/half-space Contact Problem

The three-dimensional analysis of contact mechanics is still not an easy task. Frozen stress techniques in photoelasticity have been used very much to obtain the stress fields developed in the models. Although the means to avoid the introduction of residual stresses are well established, these techniques remain time consuming. Owing to the recent developments in technology of image recording and processing, new non-destructive methods have been developed to circumvent these difficulties. In this paper, a new non-destructive method of optical slicing of a photoelastic model was used to analyse stresses developed in a half space by a rigid cylinder. The basic idea is to use the properties of polarization of the scattered light. The slice is isolated in the model by two laser sheets. A speckle pattern due to the interference of the light beams of each section in the direction perpendicular to these plans can be observed. The possibility of interference depends on the birefringence of the isolated slice. A high resolution CCD camera is used to take pictures of the two illuminated sections. The stress field can then be analyzed using software. This technique allows us to visualise photoelastic fringes at any given position within the model. Comparisons are made between experimental fringes and calculated fringes obtained by a numerical analysis using “Castem” package. The obtained results show close agreement between numerical predictions and the experimental results.

Residual stresses in LENS ® components using neutron diffraction and contour method

During manufacturing of components by laser engineered net shaping (LENS ®), a solid freeform fabrication process, the introduction of residual stresses causes deformation or in the worst case, cracking. The origin is attributed to thermal transients encountered during solidification. In the absence of reliable predictive models for the residual stresses, measurements are necessary. Residual stresses were measured in LENS ® samples of 316 stainless steel and Inconel 718 having simple geometrical shapes by both neutron diffraction and the contour methods. The results by the two methods are compared and discussed in the context of the growth direction during the LENS ® process. Surprisingly, the residual stresses are practically uni-axial, with high stresses in the growth direction.

Effect of Cavitation Number on the Improvement of Fatigue Strength of Carburized Steel Using Cavitation Shotless Peening

Peening can be used to produce a layer of compressive residual stress at the surface of components which are subject to fatigue or stress corrosion, thereby retarding crack initiation and/or impeding the development of new cracks and hence improving their fatigue life. We have developed a new peening method, Cavitation Shotless Peening (CSP), which makes use of cavitation impacts induced by the collapse of the cavitation bubbles to produce compressive residual stress and work hardening on the material surface. CSP is a surface enhancement technique which differs with shot peening in that shots are not used. CSP uses a submerged high-speed water jet with cavitation, herein referred to as a cavitating jet, whose intensity and occurring region can be controlled by parameters such as upstream pressure and nozzle size. Cavitation number , which is defined by the ratio of upstream pressure to downstream pressure, is the main parameter of the cavitating jet. In this paper, the pit distribution on the specimen was observed with cavitating numbers  = 0.0057 and  = 0.0142. The improvement of fatigue strength and introduction of residual stress were investigated for both conditions using carburized alloy steel (JIS SCM415). It was evident from a comparison between non-peened and cavitation shotless peened specimens that the cavitation number has influence on the fatigue strength of metallic materials. Comparison of shot peened and CSP specimens has also been discussed.