Relaxation Behavior Of Residual Stress Research Articles

Effect of Tensile Loading on the Residual Stress Relaxation Behavior of Induction Hardened SCM440 Steel with a Shallow Hardened Layer

Effect of Tensile Loading on the Residual Stress Relaxation Behavior of Induction Hardened SCM440 Steel with a Shallow Hardened Layer

Influence of residual stress and its relaxation on the corrosion bending fatigue resistance of EA4T axle steel treated by ultrasonic surface rolling

The fatigue properties and residual stress relaxation behavior of EA4T axle steel treated by ultrasonic surface rolling process (USRP) are investigated in air and corrosive environments. The result reveals that the surface roughness (Ra) is decreased from 1.42 to 0.17 μm after the USRP. A surface layer with ultrafine grains, work hardening, and compressive residual stress (CRS) is achieved by the USRP. Compared with the as-machined specimens, the USRP specimens exhibit slightly lower electrochemical corrosion resistance but superior fatigue performance in air and corrosive environments. The dislocation density is significantly decreased in the corrosive environment during fatigue loads, accompanied by a rapid relaxation of surface CRS. The influence of USRP on the corrosion fatigue performance is elucidated. The residual stress relaxation mechanism and its influence on fatigue resistance are also analyzed.

Fatigue Property and Residual Stress Relaxation Behavior of High-Energy Shot Peened Pure Zr

High-energy shot peening (HESP) was conducted on commercial pure Zr to generate a surface gradient nanostructured layer and compressive residual stress (CRS). The microstructure, residual stress, and fracture morphology were investigated by electron back scattering diffraction (EBSD), scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD), respectively. Tensile fatigue tests were conducted and the fatigue property was presented through S-N curve. By the XRD measurement, the residual stress relaxation and the microstructure evolution on the HESPed surface were studied under different stress amplitudes. The results indicated that the fatigue limit of the HESPed sample was 23% higher than that of the as-received. The relaxation of residual stress was observed during fatigue loading; the initial relaxation rate was fast and the later was slow, accompanied by a similar degree of nanocrystalline coarsening and dislocation density reduction. A linear relationship between the surface residual stress and the number of cycles for the HESPed sample was quantitatively described. The higher the applied stress amplitude was, the faster the residual stress relaxation (RSR) was. The stress amplitude had an important influence on the relaxation rate, the degree of nanocrystals coarsening, and dislocation density. Local plastic deformation caused grain coarsening and dislocation density reduction.

Residual Stress Measurement of Quenching Induction Hardened Axle Shaft by Contour Method and NumericalAnalysis of Residual Stress Relaxation behavior Induced by Bending Correction Process

Residual Stress Measurement of Quenching Induction Hardened Axle Shaft by Contour Method and NumericalAnalysis of Residual Stress Relaxation behavior Induced by Bending Correction Process

Evaluation of the Compressive Residual Stress Relaxation Behavior by <i>in situ</i> X-ray Stress Measurement

Evaluation of the Compressive Residual Stress Relaxation Behavior by <i>in situ</i> X-ray Stress Measurement

Mechanism for stress relaxation behavior of the residual stress improving treatments with water jet peening and buffing

In this study, the relaxation behavior of the compressive residual stress in nickel-based alloy 600 caused by water jet peening (WJP) and buffing stress improving treatments has been investigated, through the hardness reduction kinetic analysis, electron back scattered diffraction (EBSD) crystal orientation analysis and positron annihilation spectroscopy analysis. Hardness reduction behavior in WJP and buffing processed samples during thermal aging has been found to follow the Johnson-Mehl-Avrami equation and the rate constant for hardness reduction to be expressed by the Arrhenius equation. According to the result of EBSD crystal orientation analysis, it has been confirmed that the strain is introduced in the mainly surface region, which is corresponding to the hardness measurement results. Positron lifetime measurement using positron annihilation lifetime spectroscopy has revealed that the positron lifetime of the WJP and buffing processed samples is larger than that of solution heat-treated sample, indicating the lattice defects have been introduced with the stress improvement process. In addition, it becomes apparent that a large amount of vacancies introduced have disappeared after thermal aging, however some parts of dislocations have still remained. On the basis of the results, the mechanism for the stress relaxation behavior of the residual stress improving treatment effects with water jet peening and buffing has been discussed.

Relaxation Behavior of Residual Stress on Deck-to-Rib Welded Joints by Fatigue Loading in an Orthotropic Bridge Deck

To accurately evaluate the influence of the actual tension and compression state and stress ratio at the deck-to-rib welding seam position on the fatigue life of a bridge deck, this paper establishes a coupled stress analysis model that considers the welding residual stress and vehicle stress. Taking the Jiangyin Bridge as an example, a qualitative analysis of the fatigue life under the vehicle load and residual stress field is carried out using the proposed method. A case analysis showed that when the residual tensile stress in the welding seam position is superimposed on the mainly tensile cyclic vehicle load stress, the longitudinal stress relaxation exceeds the peak vehicle load stress; significant longitudinal stress relaxation occurred, while the transverse stress relaxation is not significant. However, when the residual tensile stress is superimposed on the mainly compressive cyclic vehicle load stress, the relaxations of both the longitudinal and transverse stresses are not obvious. Compared with the stress state of the welding point under the action of only the vehicle stress, when the coupling effect of the residual stress and vehicle stress is considered, i.e., the loading condition, the fatigue stress state of the weld point has undergone an essential change under cyclic compressive stress, that is, the compressive stress state that does not require a fatigue check is changed to the tensile stress state. Although the fatigue state of the tensile stress cycle condition has not changed, the fatigue life is reduced by varying degrees under either the compressive or tensile condition.

Effect of thermal relaxation on residual stress and microstructure in the near-surface layers of dual shot peened Inconel 625

Thermal relaxation behavior of residual stress and microstructure in the near-surface layers of dual shot peened Inconel alloy 625 was investigated by X-ray diffraction method. Residual stress on the top surface layer was significantly relaxed in the first 15 min at the elevated temperatures of 500°C, 600°C, and 700°C. However, there was still high maximum compressive residual stress in subsurface layers. The relaxation behavior of residual stress has contributed to the thermally activated process. The activation enthalpy Δ H and m were calculated according to the Zener–Wert–Avrami method, the values of which were 1.59 eV and 0.4934, respectively. Microstructural evaluation revealed that it was slightly changed in the near-surface layers after various isothermal treatments. Accordingly, high level of compressive residual stress and dislocation density resulted in the retained mechanical properties of dual shot peened Inconel 625, which was discussed based on the relaxation of microstructure and microhardness.

Consequences of deep rolling on the fatigue behavior of steel SAE 1045 at high loading amplitudes

Near surface sample volumes play an important role in terms of safety and reliability of technical components especially in the case of fatigue loading. By applying mechanical surface treatment methods such as shot peening, deep rolling or laser shock peening, near surface layers can be tailored resulting in increased fatigue strength especially in the high-cycle fatigue regime. For higher loading amplitudes, increase in fatigue strength, however, is less pronounced and even detrimental consequences of deep rolling treatments have been observed. To identify the reasons for these observations, the cyclic deformation behavior of differently deep rolled, quenched and tempered sample conditions of steel SAE 1045 under high loading amplitudes has been studied and assessed with a focus on the stability of near surface residual stresses. Based on the results, it is shown that the residual stress relaxation behavior in deep rolled material conditions is strongly affected by the cyclic yield strength of each material state and, thus, is related to cyclic plastic deformation. Furthermore, residual stress stability and plastic strain depend on the stress amplitude and are closely related to each other.

レーザピーニング施工面の圧縮残留応力に及ぼす外部応力負荷の影響

Peening is the process which is able to be generated compressive residual stress and is known to be effective for preventing SCC initiation and improvement of fatigue strength. Laser peening is used for the nuclear power plant components in order to prevent SCC initiation. Although it is reported that the compressive residual stress decreases due to applied stresses under general operating condition, the change of residual stress might be large under excessive loading such as an earthquake. The objectives of this study are to evaluate the relaxation behavior of the compressive residual stress due to laser peening and to confirm the surface residual stress after loading. Therefore laser peened round bar test specimens of SUS316L which is used for the reactor internals of nuclear power plant were loaded at room temperature and elevated temperature and then surface residual stresses were measured by X-ray diffraction method. In the results of this test, it was confirmed that the compressive residual stress remained after applying uniform stress larger than 0.2 % proof stress, and the effect of cyclic loading on the residual stress was small. The effect of applying compressive stress on the residual stress relaxation was confirmed to be less than that of applying tensile stress. Plastic deformation through a whole cross section causes the change in the residual stress distribution. As a result, the surface compressive residual stress is released. It was shown that the effect of specimen size on residual stress relaxation and the residual stress relaxation behavior in the stress concentration region can be explained by assumed stress relaxation mechanism.

The Effect of Specimen Dimension on Residual Stress Relaxation of the Weldments

The purpose of this study is to evaluate the residual stress relaxation behavior in weldments. The stress relaxation is studied while successively reducing the size of weld specimens. Finite-element modeling was used to simulate the stress relaxation, and then an empirical model was derived based on the experimental and modeling results. The results of this study shall encourage industry users to utilize more plentiful conventional X-ray diffractometers for residual stress measurement of large weld components.

Fatigue Life Numerical Prediction of Butt Welded Plate under Cyclic Loading

Fatigue failure of welded structure has been highly concerned in structural engineering field. At present, the numerical simulation method has been actively applied on fatigue life prediction of welded structures. In this paper, welding residual stress of a butt welded plate was simulated by thermal elastic-plastic finite element method, and welding residual stress relaxation behavior under overload was analyzed. Then, the fatigue life of the welding plate under cyclic loading was numerically predicted with considering the welding residual stress and welding residual stress relaxation, and the result was compared with that calculated according to current steel structures design code of China. The results show that, considering fatigue reliability, the fatigue life calculated based on design formulas of the steel design code is more conservative, and numerical method for fatigue life prediction of welded structures, considering the welding residual stress and welding residual stress relaxation, is a feasible method.

The Evolution of Residual Stress and Microstructure in Shot Peened S30432 Austenitic Stainless Steel at High Temperatures

The thermal relaxation behavior of residual stress and microstructure at high temperatures in S30432 austenitic stainless steel after shot peening was investigated by X-ray residual stress analyzer. The effects of exposure time and applied temperature on the residual stress and microstructure relaxation were particularly analyzed and discussed. A significant decrease of the residual stress values were observed in the first period of exposure time, followed by slowing down and then stabilization. It was also observed that a higher applied temperature produced greater relaxation. In terms of microstructure, the domain size and micro-strain were calculated by Voigt method, the results showed that the refined domain size and high micro-strain induced by shot peening were greatly relaxed at the first stage of annealing, then stabilized. With higher annealing temperature, the recrystallization behavior in the shot peened deformed layer was more obvious. Based on the results of line profile analysis, the recrystallization activation energy and micro-strain relaxation energy were calculated, respectively.

The Residual Stress Relaxation Behavior of Weldments During Cyclic Loading

Accurate measurement of residual stress is necessary to obtain reliable predictions of fatigue lifetime and enable estimation of time-to-facture for any given stress level. In this article, relaxation of welding residual stresses as a function of cyclic loading was documented on three common steels: AISI 1008, ASTM A572, and AISI 4142. Welded specimens were subjected to cyclic bending (R = 0.1) at different applied stresses, and the residual stress relaxation existing near the welds was measured as a function of cycles. The steels exhibited very different stress relaxation behaviors during cyclic loadings, which can be related to the differences in the microstructures of the specimens. A phenomenological model, which treats dislocation motion during cyclic loading as being analogous to creep of dislocations, is proposed for estimation of the residual stress relaxation.

Thermal Relaxation Behavior of Residual Stress and Microstructure in Shot Peened S30432 Steel at Elevated Temperatures

The thermal relaxation behavior of residual stress and microstructure at elevated temperatures in S30432 austenite steel after shot peeningwas investigated by X-ray residual stress analyzer. The effect of the exposure time and the applied temperature on the residual stress andmicrostructure relaxation was particularly analyzed and discussed. A significant decrease of the residual stress values and peak breadth wasobserved in the first period of exposure time, followed by slowing down and then stabilization. It was also observed that a higher appliedtemperature produced greater relaxation. The relaxation behavior could be described by Zener­Wert­Avrami function. The thermal stability ofmicrostructure was higher than that of the residual stress. Both of the activation enthalpy of residual stress and microstructure relaxation werehigher than that of iron self-diffusion in £-Fe. [doi:10.2320/matertrans.M2012058](Received February 15, 2012; Accepted March 26, 2012; Published May 25, 2012)Keywords: thermal relaxation, residual stress, microstructure, S30432 austenite steel

Thermal relaxation behavior of residual stress in laser hardened 17-4PH steel after shot peening treatment

In order to investigate the residual stress relaxations of shot peened layer, isothermal annealing treatments were carried out on tempered and laser hardened 17-4PH steel after shot peening with different temperatures from 300°C to 600°C. The results showed that the residual stresses were relaxed in the whole deformation layer especially under higher temperature. The maximum rates of stress relaxation took place at the initial stage of annealing process in all conditions. The relaxation process during isothermal annealing could be described by Zener–Wert–Avrami function. The thermal stability of residual stress in tempered 17-4PH was higher than that in laser hardened 17-4PH as well as that in α-iron, which was due to the pinning effects of ɛ-Cu precipitates on the dislocation movement. As massive ɛ-Cu precipitates formed in the temperature about 480°C, the activation enthalpies for stress relaxation in laser hardened 17-4PH were the same as that in tempered 17-4PH in the conditions of isothermal annealing temperatures of 500°C and 600°C.

Relaxation Behaviour of Laser Peening Residual Stress due to Mechanical Loading on Aluminum Alloy

The relaxation behavior of residual stress induced by laser peening during mechanical loading was investigated on an aluminum alloy A2024. The residual stress relaxation process was measured by x-ray diffraction method and analyzed by a finite element method (FEM). The plastic deformation behavior was evaluated from the x-ray diffraction peak width and the FEM. The surface residual stress relaxation under tensile loading occurred when the plastic-deformation started at the inside of material where the balancing tensile residual stress existed. Under the compressive loading, the surface residual stress relaxation started due to the plastic deformation beneath the surface where the maximum compressive residual stress existed. The plastic deformation at the inside of material caused the redistribution of the residual stress and resulted in the relaxation of the surface residual stress. For both tensile and compressive loading, the surface compressive residual stress relaxation occurred before the total stress ( = (residual stress) + (applied stress)) at the surface reached the yield condition. All discussions in this study based on the mechanical deformation behaviour of the material. Therefore, the conclusions of this study are thought to be able to apply to the behavior of the residual stress under the mechanical loading on metallic materials treated by any mechanical surface treatment.

Residual stress relaxation during heating of bearing rings produced in two different manufacturing chains

Bearing rings produced in two different manufacturing chains have been investigated in terms of residual stress relaxation behavior during heating. Cold rolled rings present almost constant compressive residual stresses at the external periphery and completely affected cross sections. Machined rings show high tensile residual stress with periodic variations along the outer periphery caused by clamping during machining. Residual stress states then are confined in a very thin layer. With increasing temperature residual stresses relax. Machined rings present a progressive loss of the residual stress periodicity with increasing temperature. The cold rolled rings show a different relaxation behavior between surface and core. Complementary investigations revealed that recrystallization occurs at a higher temperature in the core compared to the surface. The surface of cold rolled rings and machined rings present a similar behavior: recovery processes induce a decrease of residual stresses at temperatures up to 500 °C and recrystallization starts above 500 °C which causes a complete residual stress relaxation. In the core of cold rolled rings, recovery processes are still active until 600 °C where recrystallization begins. However, residual stresses in the core are already completely relaxed at 600 °C.

Residual stress field and thermal relaxation behavior of shot-peened TC4-DT titanium alloy

Shot peening is an effective surface treatment method, which can improve the fatigue properties of metallic materials. In the present paper, the residual compressive stress field induced in TC4-DT titanium alloy under different shot peening conditions and the thermal relaxation behaviors of shot-peened TC4-DT were discussed. The shot peening can cause residual compressive stress on the material surface compared to un-peened materials. The subsurface residual stress distributions of original and shot-peened specimens were measured by an X-ray diffraction method. The residual compressive stress profiles accord with the characteristic curve of residual stress field. The maximum residual compressive stress is located at subsurface layer. Surface roughness also increases with increasing shot peening intensity. There is relaxation of residual compressive stress during temperature. Thermal relaxation behavior of residual stress was studied at 150 and 300 °C with different ageing time. The residual stress relaxation is influenced by temperature and time during ageing. Thermal relaxation of residual stress is a thermal recovery process. The relaxation process of thermal residual stress is analyzed by applying the Zener–Wert–Avrami function.

Stress relaxation behavior of shot-peened Ti–6Al–4V under fretting fatigue at elevated temperature

Relaxation behavior of residual stress in a shot-peened titanium alloy, Ti–6Al–4V subjected to fretting fatigue was investigated at room and elevated temperatures. Constant amplitude fretting fatigue tests were conducted at several maximum stress levels, σ max ranging from 333 to 666 MPa with a stress ratio of 0.1. Two heaters, placed at the front and back of specimen, were used to heat and maintain the temperature in the gage section of specimen at 100 and 260 °C. Residual stress was measured using the X-ray diffraction method. There was relaxation of residual compressive stress during fretting fatigue at room and elevated temperatures, which in turn manifested in the reduction of fretting fatigue life. Greater stress relaxation occurred when higher temperature, stress range and contact load were applied, however, contact load had a considerably smaller effect. Stress relaxations due to elevated temperature and mechanical load (i.e. fretting fatigue) were found to be independent processes within the test conditions of this study, such that they can be linearly superimposed to predict the total stress relaxation from fretting fatigue at elevated temperature.