Residual Stress Values Research Articles

Surface modification of fully austenitic stainless steel SMO 254 by laser shock peening to induce compressive residual stress

ABSTRACT The laser shock peening process was conducted with varying pulse densities on the SMO 254 material. The formation of an α martensitic layer from the austenitic structure was witnessed after conducting the laser shock peening process, with the migration of elements across the grains. The increase in the surface roughness value, measured by the Atomic force microscope and Mahr surface profilometer, is directly proportional to the rise in pulse density. An elevated value of compressive residual stress of −786 MPa and a higher Vickers micro hardness value of 365 HV were obtained in the specimen where a pulse density of 6000 pulse/cm2 was applied.

Determination of the Effect of Heat Input during Laser Welding on the Magnitude of Residual Stresses in the Refurbishment of Al Alloy Casting

The paper presents the results of research on the evaluation of the quality of coating layers made by a laser. The base material, which was Dievar steel (1.2343), was coated with a single layer using additional materials in the form of a wire with a diameter of ø 1.0 mm. As additional material, wires with chemistry corresponding to steels 1.2343 and 1.6356 were used. The primary objective was to verify the possibilities of innovative use of additive materials based on maraging steels, which were chosen from the production of two manufacturers with slightly different chemical compositions. The experiment verified the influence of the cladding parameters on the residual stress values around the fabricated maraging layers. Metallographic analysis by light microscopy was carried out in order to identify the individual structures as well as to assess the occurrence of internal defects in the coatings. The effect of the mixing of the coating metal with the base material was also assessed by means of a low-load hardness assessment, which was carried out in accordance with EN ISO 4063-2. Based on the results, it can be concluded that, in terms of residual stresses, the measured values were approximately the same for all the additive materials used; however, due to the desired mechanical properties of the additively formed layers, it is possible to recommend additive materials based on medium- and high-alloy steels for additive manufacturing.

Microstructure and residual stress analysis as heat treatment of additive manufactured A356.2 alloy by powder bed fusion

Aluminum alloys are commonly used in additive manufacturing (AM) because of their high specific strength and low weight. However, the high energy used in the AM process to overcome heat reflectivity induces thermal gradients and residual stress in the products. This study, A356.2 alloy was used for AM, and the residual stress and microstructure generated during this process were observed. X-ray diffraction (XRD) and nanoindentation were used to measure the surface residual stress, while the residual stress inside the material was measured using neutron diffraction. During the nanoindentation tests, we varied the indentation load conditions and compared the results with the residual stress values measured using XRD. To relieve the residual stress, we conducted a heat treatment and analyzed the changes. For surface residual stress, tensile residual stress (27∼91 MPa) in the as-built samples changed to compressive residual stress (‐28∼49 MPa) after heat treatment, with higher heat treatment temperatures producing stronger compressive residual stress. As for the internal residual stress, it was generally relaxed after heat treatment. As indentation depth increased, the residual stress results became similar to the residual stress values measured by XRD. In addition, the electron channeling contrast imaging (ECCI) technique was used for observation of lattice defects within precipitates generated and coarsened by heat treatment. We assessed the efficiency of each measurement method by comparing the results obtained through different techniques.

Stress Distribution of EH40 with Defects Considering Solid-State Phase Transformation

Residual stress of laser-welded marine steel EH40 was experimentally and numerically analyzed considering weld defects (collapse, hump, and unfitness) and solid-state phase transformation (SSPT). A double-cylindrical source model was used to simulate the temperature distribution. The mean prediction errors of the model without and with weld defects along the plate thickness were 9.2 and 3.5%. Based on the thermodynamics of SSPT, microstructure fractions were computed and verified by weld hardness test results. Under the effect of SSPT, residual stress changed from compressive stress to tensile stress with the increase of the distance from the weld center. Weld defects have an influence on the value of residual stress, and this effect was greater when SSPT was considered. The affected zone extended from the vicinity of weld defects to the whole weld. The variations of longitudinal residual stress (LRS) and transverse residual stress (TRS) caused by weld defects and SSPT both exceeded 150 MPa. LRS was mainly affected by the loss and increase of metal, while TRS was affected by the stress concentration caused by shape geometry changes. Thus, the influence of weld defects on TRS was greater than that on LRS. The proposed finite element model considering weld defects and SSPT can be used to accurately predict residual stress in laser welding of marine steel EH40 and provide a theoretical basis to reduce welding stress.

Spatial and temporal crack initiation prediction in steels based on residual stress tensor distribution monitoring

We have developed a method and the corresponding instruments, able to provide the spatial and temporal determination of crack initiation in ferromagnetic steels and their welds. The method is based on the monitoring of the differential magnetic permeability µr along the length of the steel, since a sigmoid monotonical dependence of µr on residual stresses has been determined in the past. Thus, the magnetic stress calibration (MASC) curves can inform on the localized residual stresses. Therefore, the temporal stress monitoring at different areas of interest can inform about the status of residual stresses. Then, the tendency of the residual stress value can inform about reaching the positive (tensile) or negative (compressive) yield point of the steel. As an example, a quasi-parabolic temporal dependence of µr offers the tendency to determine the time, or the time window, required to reach yield point. This way, the temporal prediction of the crack initiation is provided for the given point in space, since reaching the yield point results in crack initiation.

Rolling Contact Fatigue Damage Analysis of G10CrNi3Mo Steel Bearing Inner Ring by X-ray Measurements

Contact fatigue is the main failure model for bearing systems in steel rolling mills. Characterizing the degree of contact fatigue damage is important for predicting its operating life. In this paper, the X-ray diffraction method (XRD) is used to measure the residual stress state and the diffraction peak width (FWHM, full width at half maximum) of six samples with different degrees of contact fatigue failure. The results show that surface residual stress values increased by more than 70% compared with the original state, while the diffraction peak width values decreased by more than 7% and were strongly correlated with the degree of contact fatigue damage. The XRD measurement of the bearing inner ring enables the characterization of the evolution of the residual stress state and grain distortion due to damage development. FWHM values may be considered an indicator for predicting the degree of contact fatigue.

Development of Maximum Residual Stress Prediction Technique for Shot-Peened Specimen Using Rayleigh Wave Dispersion Data Based on Convolutional Neural Network

Shot peening is a surface treatment process that improves the fatigue life of a material and suppresses cracks by generating residual stress on the surface. The injected small shots create a compressive residual stress layer on the material’s surface. Maximum compressive residual stress occurs at a certain depth, and tensile residual stress gradually occurs as the depth increases. This process is primarily used for nickel-based superalloy steel materials in certain environments, such as the aerospace industry and nuclear power fields. To prevent such a severe accident due to the high-temperature and high-pressure environment, evaluating the residual stress of shot-peened materials is essential in evaluating the soundness of the material. Representative methods for evaluating residual stress include perforation strain gauge analysis, X-ray diffraction (XRD), and ultrasonic testing. Among them, ultrasonic testing is a representative, non-destructive evaluation method, and residual stress can be estimated using a Rayleigh wave. Therefore, in this study, the maximum compressive residual stress value of the peened Inconel 718 specimen was predicted using a prediction convolutional neural network (CNN) based on the relationship between Rayleigh wave dispersion and stress distribution on the specimen. By analyzing the residual stress distribution in the depth direction generated in the model from various studies in the literature, 173 residual stress distributions were generated using the Gaussian function and factorial design approach. The distribution generated using the relationship was converted into 173 Rayleigh wave dispersion data to be used as a database for the CNN model. The CNN model was learned through this database, and performance was verified using validation data. The adopted Rayleigh wave dispersion and convolutional neural network procedures demonstrate the ability to predict the maximum compressive residual stress in the peened specimen.

Integrity Assessment of Stress Corrosion Cracking Susceptibility of Duplex UNS S32205 and Austenitic UNS S31653 Stainless Steel Reinforcements

Herein, the stress corrosion cracking (SCC) susceptibility of duplex (UNS S32205) and austenitic (UNS S31653) stainless steel (SS) reinforcements was evaluated using integrity assessment criteria. Mechanical properties were analyzed and compared by different SCC susceptibility factors. The integrity assessment was conducted applying Cosenza, Creazza, and Ortega ductility criteria, following three different standards (ACI 318-19, ASTM A615, and FIB). A conventional carbon steel (UNS G10080) reinforcement was also evaluated for comparative purposes, whose high residual stress value (>280 MPa) promoted a high corrosion growth rate. Duplex UNS S32205 SS grade showed a significant decrease in elongation, leading to failure after ductility assessment at high chloride concentrations. Fractographic analysis of both SS grades, duplex and austenitic, revealed less than 40% brittle areas at 8 wt.% Cl−, while UNS G10080 had over 85% at 4 wt.% Cl−.

Corrugated steel web I-girder welding deformation and residual stress research

The distribution law of residual stresses in the welding of corrugated steel web I-girders is still unclear. It is investigated by a combination of experiments and numerical simulations. The three-dimensional thermoelastic finite-element model of corrugated steel web and conventional flat web I-girders were established. Use the resistance strain gauge method to measure the residual stress in the welded corrugated steel web I-girders to verify the correctness of the established finite element model. Analysis of welding residual stress distribution and deformation of two types of I-girders through experimental data and numerical simulation data. The results show that the established finite-element model is correct, and the experimental residual stress values are matched with the simulated values. Two different web I-girders have significant differences in their welding residual stress distribution. At the same time by the two deformation curve can be seen, welding deformation and web shape related.

Coil Spring Failure Analysis Reviewed from Residual Stress, Crytal Orientation, and Texture

Crystal defects can be identified through the crystallographic characteristics of crystal orientation (lattice), microstrain, and texture. Identification of crystal defects on the atomic scale through crystallography is very important in analyzing the mechanism of material properties due to the influence of dislocations. The slip mechanism is analyzed to minimize coil spring failure. This study aims to analyze the causes of coil spring failure based on crystallography. XRD testing was carried out for analysis of residual stress, crystal orientation, and texture using MAUD 2.94 version software. Hardness testing was carried out on the surface of the coil spring with locations near and far from the fracture using micro Vickers. The macro fracture morphology was analyzed using a DSLR camera and the micro fracture morphology was analyzed using SEM. The XRD result shows that the coil spring material has a tensile residual stress value of "202.4 ± 15.9 MPa" with the resulting crystal orientation showing the hkl (100), (200), (211), (200) fields. The plane (200) has a texture characteristic that is oriented towards the Rolling direction along the spring axis. Texture oriented towards Rolling Direction can be shown with a maximum probability value of 1.191. A high probability will have an impact on the presence of material surface defects. Surface defects are indicated by the presence of pit corrosion on micro and macro fracture morphology observations. The pit corrosion defects that occur in the failed coil springs are the beginning of the formation of crack initiation and cause stress concentration. The stress concentration will increase with loading and cause crack propagation.

ANALYSIS OF ADDITIVELY MANUFACTURED AlSi10Mg ALLOY USING X-RAY DIFFRACTION

This research deals with the study of additively manufactured AlSi10Mg alloy samples by X-ray diffraction. The effect of sample orientation during 3D printing by Selective Laser Melting on the values of macroscopic residual stresses and microstructural parameters and their possible inhomogeneities of the cylindrical sample was investigated. Phase analysis identified the intermetallic phase Mg2Si in addition to the major phases (solid solutions of Al and Si). Tensile residual stresses weredetected in the surface layer for all samples. Inhomogeneities of the investigated parameters of all samples were observed along the circumference of the shank. These effects may be related to the direction of the layers relative to the axis of the sample. These inhomogeneities form so-called microstructural notches or weak spots that are prone to the formation of fatigue cracks, which have a major influence on the fatigue life.

Investigation of residual stresses and modeling of tensile deformation in wire-arc additive manufactured 6061 aluminum alloy: Diffraction and elastoplastic self-consistent model

The aim of this work is to study the mechanical behavior of 6061 aluminum walls produced by Wire Arc Additive Manufacturing at the different scales of the material. The residual stresses of the parts are characterized on the surface and in the bulk thanks to X-ray and neutron diffraction techniques, respectively. Although the residual stress values determined in the close-surface are low (40 MPa for the maximum value), the mechanical state is different in depth with significant maximum residual stress levels ( ± 100 MPa). Tensile tests carried out on samples extracted from a WAAM wall in three orientations reveal that the mechanical properties of the manufactured material are slightly better compared to conventional material in T6 state. In situ X-ray diffraction experiments have also been performed under uniaxial tensile testing in order to determine strain pole figures. An elasto-plastic self-consistent model considering the microstructural characteristics and the main physical phenomena governing the material behavior, is proposed. The model agrees with the experimental data and the simulations reproduce the main features observed at the scale of the diffracting volume.

Numerical simulation and experimental study of residual stress in dissimilar aluminum alloy laser composite welding

The study combined experimental and numerical simulation methods to investigate the distribution of residual stress in laser composite welding of dissimilar aluminum alloys 6063 and 5083. Using the Simufact Welding simulation software and a combined volume heat source, the distribution patterns of transverse and longitudinal residual stress fields at different welding speeds were analyzed. The blind hole method was used to test the residual stress after welding. The results showed that the use of a combined volume heat source model for heat source calibration yielded ideal results, and the thermal cycle curve was basically consistent with the simulation and experimental results of residual stress. As the welding speed decreased, the longitudinal residual stress of the parent material on both sides significantly decreased, while the transverse residual stress increased. The majority of tensile and compressive stresses on both sides of the 5083 and 6063 aluminum alloys decreased with a decrease in welding speed. The Von Mises equivalent stress indicated that the cooling process is the main stage for residual stress generation. When the welding speed decreased, the peak value of longitudinal residual stress on the 6063 aluminum alloy side decreased from 230 to 90 MPa, while that on the 5083 aluminum alloy side decreased from 304 to 150 MPa. These findings provide an important basis for controlling and reducing the residual stress and deformation of dissimilar aluminum alloy laser arc composite welded components.

Abnormal mechanical hysteresis behavior of Tyranno-ZMI SiC/SiC containing Ti3Si(Al)C2

This work studied the effect of tough phase Ti3Si(Al)C2 on the mechanical hysteresis behavior of SiC/SiC. Different from continuous fibers reinforced brittle ceramic matrix composites, the mechanical hysteresis behavior of SiC/SiC containing Ti3Si(Al)C2 shows some abnormal phenomena: as peak applied stress increases during cyclic loading-unloading-reloading tests, the thermal residual stress values exhibit highly dispersion and the thermal misfit relief strain shows abnormally slow growth. These abnormal phenomena are caused by the reduction of transvers cracks (perpendicular to loading fibers) and the generation of hoop cracks (parallel to loading fibers). The plastic deformations of Ti3Si(Al)C2 prevents the transverse cracking of modified matrix, while promoting the hoop cracking of SiC matrix prepared by chemical vapor infiltration (CVI-SiC). Hoop cracking occurs within the transition zone containing amorphous SiO2 layer and carbon layer in CVI-SiC matrix. The combination of weak transition zone and strong modified matrix finally leads to the occurrence of hoop cracking.

Hybrid surface implants: Influence of residual stress on mechanical behavior, evaluated by finite element analysis and validation by fatigue tests

ObjectivesTo determine the influence of different surface roughness and residual stress of hybrid surface implants on their behavior and mechanical failure. MethodsThree types of implants with different surface roughness were used as specimens: smooth, rough, and hybrid. A diffractometer was used to determine the residual stress of the implants according to their different surface treatment. These results were used as an independent variable in a finite element analysis that compared the three specimens to determine the von Mises stress transferred to the implants and supporting bone and the resulting microdeformations. Flexural strength and fatigue behavior tests were performed to compare the results of the three types of implants. ResultsHigher residual stress values were found for rough surfaces (p < 0.05, Student’s t-test) compared to smooth surfaces, and both types of stress were different for the two types of hybrid implant surfaces. Finite element analysis found different von Mises stress and microdeformation results, both at the level of the implant and the bone, for the three types of implants under study. These results were correlated with the different flexural strength behaviors (lower resistance for hybrids and higher for rough surfaces, p < 0.05) and fatigue behavior (the rough implant had the longest fatigue life, while the hybrid implant exhibited the worst fatigue behavior). SignificanceThe results show a trend toward a less favorable mechanical behavior of the hybrid implants related to the retention of different residual stresses caused by the surface treatment.

Residual stresses in circular steel tubular columns repaired by laser-cladding additive manufacturing

This paper presents a study that investigates the magnitude and distribution of residual stress (RS) in laser cladding (LC) repaired circular steel tubular columns. The study involves experimental tests and numerical simulation. The familiar blind-hole method is employed in the experimental investigation for two RS measurement tests, while the finite element method is used for numerical thermal-mechanical analysis to obtain the temperature field and RS field. The results indicate the presence of residual tensile stress in the LC sheet and its surrounding area. The RS in the LC sheet area and in the vicinity of the LC sheet-substrate boundary is much greater than that in the substrate area located far away from the LC sheet. Additionally, the RS in the LC sheet along the scanning direction is larger than that perpendicular to the scanning direction. Nevertheless, the RS values in both the LC sheet and substrate are less than their respective yield strength values. The temperature-time cooling curves obtained from the finite element analysis, which simulate the laser cladding process for repairing the circular steel tubular column, are used to develop a theoretical model for predicting the RS in the LC sheet. A simplified RS model is proposed based on the thermal-mechanical theory, utilising the linear-exponential two-stage cooling curve. Comparisons between the experimental results and the theoretical results that are predicted using the proposed simplified RS model show both results to be in good agreement. Therefore, the simplified RS model proposed in this paper is suitable for efficiently and accurately predicting the RS in LC sheet for circular steel tubular columns repaired by LC.

Nitriding layer characteristics of modified AISI422 martensitic stainless steel in tempered state

In this study, the nitriding layer of the modified AISI422 martensitic stainless steel was characterized by several method, including optical microscopy (OM), micro-hardness tester, X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM), to study the phase transformation at the whole nitriding layer during the plasma nitriding. In order to investigate the evolution of the nitriding process the TEM samples of the nitriding layer has been prepared from the white layer to the un-nitriding zone by the focus ion beam method. With nearly 20 h nitriding process, the white layer, vein-like structure and the diffusion zone was clearly observed though the OM. Together, the TEM results show that the γ′-Fe4N and the micro holes existed in the white layer and the thick vein-like structure. And the morphology of the continuous precipitation of CrN was highly related with the depth of the nitriding layer. Excepted the normal coarsening mechanism, the EDS results indicate that the discontinuous precipitation of CrN may also originate from the transformation of the M23C6(M=Cr) during the nitriding process. Meanwhile, the residual stress value is not directly proportionate to the nitriding depth or the N contents. Furthermore, it could be affected by the N contents and the degree of the CrN spinodal decomposition, and these two factors lead the maximum value of the compress stress appears at the depth of 120μm.

Estimation of residual stress relaxation in low alloy steel with different hardness during fatigue by in situ X-ray measurement

In situ X-ray stress measurements were conducted to investigate the relaxation of compressive residual stress induced by fine particle peening during fatigue. To quantitatively assess the stability of the compressive residual stress, a concept of relaxation threshold stress was proposed. The relaxation threshold stress, which indicates the stability of the compressive residual stress, showed a direct correlation with specimen hardness. If the combined value of the compressive residual stress and compressive applied stress surpass the relaxation threshold stress, then the compressive residual stress relaxes. The relaxation threshold stress can be used to estimate the relaxation that occurs during fatigue.

Oxidation resistance and mechanical properties of AlTiZrHfTa(-N) high entropy films deposited by reactive magnetron sputtering

(AlTiZrHfTa)1−xNx refractory high entropy films (RHEFs) were deposited by direct current magnetron sputtering in various nitrogen ratios (RN2 = N2/(Ar+N2)) on flat glass, silicon and sapphire substrates. The nitrogen-free film is amorphous while the nitrides are single-phased solid solutions with Face-Centered Cubic (FCC) structures. The hardness increases from 6.4 GPa for the nitrogen-free film to 25.3 GPa for the film obtained at RN2 = 20%. A preferred orientation from (111) to (200) occurs when RN2 increases from 5% to 50%. H/E and H3/H2 reports show high values for the film deposited at RN2 = 20% compared to that at 10%. However, this latter has the best compromise in terms of mechanical properties related to a lower residual stress value. The nitrides films obtained with RN2 ≥ 5%, are thermally stable at 800 °C for 3 h under vacuum. Compared to the metallic film they show an improved oxidation resistance. In fact, the Kp constant of the nitride (RN2=20%) is lower (1.22 10−7 g2 cm−4 h−1) than that of the nitrogen-free film (1.77 10−6 g2 cm−4 h−1). The corresponding activation energies (Ea) are respectively calculated at 94.8 KJ. mol−1 and 45.5 KJ.mol−1. After oxidation process, TEM analysis reveal the formation of homogeneous mixed oxide.

2D X-ray diffraction method for evaluating the local crystallization of Fe-based amorphous alloy ribbon induced by ultrashort pulsed laser local heating

Fe-based amorphous alloys, which exhibit excellent soft magnetic properties, are difficult to machine, owing to their high strength, toughness, and hardness resulting from their unique structures. The authors proposed a novel blanking method that improves the machinability by crystallizing only the local regions involved in machining, thereby reducing the local strength and toughness. Because the micro-region mechanical properties of amorphous alloys vary greatly depending on the precipitated crystal species and volume fraction, it is necessary to nondestructively investigate the type of microstructure achieved by local heat treatment to determine the appropriate blanking conditions. However, an appropriate method for investigating crystals precipitated locally in an amorphous matrix is yet to be established. In this study, we used the 2D X-ray diffraction method to investigate the local crystallization of an Fe-based amorphous alloy ribbon after local heat treatment using an ultrashort pulsed laser. Furthermore, the 2D method was used to investigate the residual stresses in the fully crystallized amorphous alloy ribbons, and the results were compared using the sin2(ψ) method. The 2D method detected the slightly precipitated crystals in a local area with a radius of about 40 µm in the amorphous matrix. The integrated intensity of the diffraction peaks can be used to predict the internal structure after local heat treatment. Furthermore, the 2D method could measure residual stress with smaller error than the sin2(ψ) method. The core-shell crystals precipitated by heat treatment exhibited a compressive residual stress of −82 MPa to −67 MPa in the core Fe3B crystals and tensile residual stress of 39–60 MPa in the shell α-Fe crystals, approximately. The residual stress values of the precipitated crystals depended on the direction of rotation of the quenching roll used in the production of the amorphous alloy ribbons.