Thermal Residual Stress Relaxation Research Articles

The effect of heat treatment on the strength and toughness of carbon fiber/silicon carbide composites with different pyrolytic carbon interphase thicknesses

The effect of heat treatment on the strength and toughness of carbon fiber/silicon carbide composites (C/SiC) with different pyrolytic carbon (PyC) interphase thicknesses was investigated. It was found that as the heat treatment temperature (HTT) increases to 1900°C, the strength and toughness of a low strength specimen (LSS, thin PyC ≈40nm) increase by as much as 43.2% and 274.0%, while those of a high strength specimen (HSS, thick PyC ≈140nm) show decreases of 25.1% and 14.8%, respectively. The elastic moduli of both LSS and HSS monotonically decreased with increasing HTT while the failure strains always became larger regardless of the initial interfacial bonding strengths (IBS). The mechanisms involved in the heat treatment of the C/SiCs were identified as (I) partial graphitization of the PyC that weakens the IBS, and (II) production of defects such as matrix cracks/delamination, interfacial debonding and fiber fracture/pull-out that lead to thermal residual stress relaxation. Thus heat treatment improves the strength and toughness of LSS with a relatively high IBS, but has a negative impact on both properties of HSS with a moderate IBS because the stress transfer efficiency onto the fibers is hindered by the too low IBS and the excessive stress relief.

Time-Dependent Deformation of CFRP Quasi-Isotropic Laminates Caused by Relaxation of Thermal Residual Stress and Physical Aging

Time-Dependent Deformation of CFRP Quasi-Isotropic Laminates Caused by Relaxation of Thermal Residual Stress and Physical Aging

Thermal relaxation of residual stress in laser shock peened Ti–6Al–4V alloy

Laser shock peening (LSP) induced residual stresses in Ti–6Al–4V, and their thermal relaxation due to short-term exposure at elevated temperatures are investigated by an integrated modeling/simulation and experimental approach. A rate and temperature-dependent plasticity model in the form of Johnson–Cook (JC) has been employed to represent the nonlinear constitutive behavior under both LSP and thermal loads. By comparing the simulation results with experimental data, model parameters for Ti–6Al–4V are first calibrated and subsequently applied in analyzing the thermal stability of the residual stress in LSP-treated Ti–6Al–4V. The analysis shows that the magnitude of stress relaxation increases with the increase of applied temperature due to material softening. Most of stress relaxation occurs before 10min to 20min exposure in this study, and stress distribution becomes more uniform after thermal exposure. An analytical model based on the Zener–Wert–Avrami formula is then developed based on the simulation results. The activation enthalpy of the relaxation process for laser shock peened Ti–6Al–4V is determined to be in the range of 0.71eV to 1.37eV.

Thermal Relaxation of Residual Stresses in Shot Peened Surface Layer of SiCw/Al Composite

The residual stress relaxation of the shot peened layer on the SiCw/Al composite during isothermal annealing was investigated. The results showed that the residual stresses relaxed in the whole deformation layer especially when the annealing temperature was higher than 200 °C. The relaxation process during isothermal annealing could be described precisely using Zener-Wert-Avrami function. Because of high intensity dislocation around reinforcements producing a large amount of stored energy, the residual stress relaxation activation enthalpy of shot peened SiCw/Al was smaller than self-diffusion activation enthalpy of pure aluminum. According to the analysis of full-width at half-maximum (FWHM) of the shot peened composite in different annealing temperatures, it can be concluded the recovery and recrystallization behavior became intensely when anneal temperature was larger than 200 °C. The small relaxation of residual stress in low annealing temperature was mainly due to partly recovery and recrystallization in a very low level.

Thermal relaxation of residual stresses in shot peened surface layer of (TiB+TiC)/Ti–6Al–4V composite at elevated temperatures

Abstract As an effective and important surface treatment method, shot peening can introduce high residual compressive stress and microstructure variation at near surface deformation layers. In this work, residual stresses relaxation behaviors of the shot peened layer of (TiB + TiC)/Ti–6Al–4V composite were investigated during thermal exposure, and the microstrain was calculated according to the integral breadth after isothermal annealing. The microstrain decreased fast and reached the minimum at 500 °C, which resulted from the thermal recovery and dynamic recrystallization. At elevated temperatures, the residual compressive stresses were relaxed in the whole deformation layers, which were caused by the thermally activated gliding of dislocations. The processes of relaxation can be described using a Zener–Wert–Avrami function and the activation energy of the residual stresses relaxation was higher than that of titanium self diffusion, which was ascribed to the hindrance effects of reinforcements as sink sources of dislocations during annealing.

Thermal Residual Stress Relaxation in Sputtered ZnO Film on (100) Si Substrate Studied <i>In Situ</i> by Synchrotron X-Ray Diffraction

Residual stress relaxation in sputtered ZnO films has been studied in-situ by synchrotron x-ray diffraction. The films deposited on (001) Si substrates were thermally treated from 25°C to 700°C. X-ray diffraction 2D patterns were captured continuously during the heating, plateau and cooling ramps. The corrections carried out for compensating the furnace drift are discussed. We first observe an increase of the intrinsic compressive stresses before stress relaxation starts to operate around 370°C. Then, thermal contraction upon cooling dominates so that overall, the large initial compressive film stresses turn to tensile after thermal treatment. The overall behaviour is discussed in terms of structural changes induced by the heat treatment.

A finite element study of thermal relaxation of residual stress in laser shock peened IN718 superalloy

The residual stresses in laser shock peened (LSP) Inconel 718 Ni-base superalloy and their thermal relaxation behavior were investigated based on three-dimensional nonlinear finite element analysis. To account for the nonlinear constitutive behavior, the Johnson–Cook model has been employed and the model parameters for high strain rate response of IN718 are calibrated by comparison with recent experimental results. Based on the LSP simulation, the thermal relaxation behavior was studied through coupled thermal-structure analysis in LS-DYNA. More specifically, the effects of test temperature, exposure time and degree of initial plastic deformation are analyzed and discussed. It is observed that stress relaxation mainly occurs during the initial period of exposure, and the relaxation amplitude increases with the increase of applied temperature and as-peened plastic deformation. Based on the simulation results, an analytical model based on Zener–Wert–Avrami function is proposed to model the thermal residual stress relaxation.

Thermal Relaxation of Residual Stresses in Nickel-Based Superalloy Inertia Friction Welds

This article describes an experimental study aimed at characterizing the extent of residual stress relaxation during thermal treatment of inertia friction-welded alloy 720Li nickel-based superalloy welded tubular rings. In the as-welded condition, yield level tensile hoop stresses were found by neutron diffraction in the weld region along with axial bending stresses (tensile toward the inner diameter (ID)/compressive toward the outer). The evolution of these residual stress levels during postweld heat treatment (PWHT) was mapped experimentally over the weld cross section. After 8 hours of PWHT, the axial stresses relaxed by 70 pct, whereas the hoop stresses reduced by only 50 pct. Some scatter of residual stress evolution was found between samples, particularly for the axial stress direction. This was attributed to substandard tooling to grip the rings. The results on subscale samples were transferred to a full-scale aeroengine (650-mm diameter) compressor drum assembly that was postweld heat treated for 8 hours. It was found that the residual stresses, particularly in the axial direction, were noticeably lower in this full-scale weld component compared to the subscale weld heat treated for the same time. The differences seem to be best rationalized by the different standards of jigging used during joining these two types of welds.

Prediction of Time-Dependent Dimensional Change Induced by Thermal Residual Stress Relaxation in CFRP Cross-Ply Laminates

In this paper, time-dependent dimensional change in a symmetrical cross-ply laminates was predicted by transverse properties of the CFRP laminates. CFRP with pitch-based carbon fiber and cyanate ester resin was chosen for the study. Viscoelastic property was obtained by performing tensile creep test for unidirectional laminates in the transverse direction. In addition, shrinkage caused by physical aging was obtained by measuring the strain change for unidirectional laminates as well. Experimental results were applied to the classical lamination theory in order to predict the time-dependent dimensional change of a symmetrical cross-ply laminates. The strain change in a symmetrical cross-ply laminates was obtained experimentally using an extensometer, and the result was compared with the prediction. From the comparison, it was concluded that the proposed prediction method is appropriate. It was also found that physical aging shrinkage must be compensated in order to evaluate the relaxation modulus from tensile creep test result. The effect of physical aging shrinkage must also be considered in prediction of time-dependent deformation in cross-ply laminates.

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.

Thermal Relaxation of Residual Stresses in Shot Peened Surface Layer on TiB<SUB>2</SUB>/Al Composite at Elevated Temperatures

The residual stresses and work hardening relaxations of the shot peened layer on the TiB2/6351Al composite during thermal exposure were investigated. The results showed that the residual stresses were relaxed in the whole deformation layers especially under higher temperatures. The relaxation processes during isothermal annealing can be described using a Zener-Wert-Avrami function. The thermal stability of work hardening is higher than that of residual stresses. And both the activation enthalpies of the residual stresses and work hardening relaxations are higher than the enthalpy of aluminum self diffusion. For residual stresses relaxation, the enthalpy increment was caused by the hindrance effects of reinforcements. While for the work hardening relaxation, the increment was caused by the combination of hindrance effects of the reinforcements and the precipitates.

S0406-1-2 非対称CFRP積層板の形状変化挙動における熱残留応力緩和の影響(プラスチック基複合材料の加工と評価(1))

S0406-1-2 非対称CFRP積層板の形状変化挙動における熱残留応力緩和の影響(プラスチック基複合材料の加工と評価(1))

Thermal Relaxation of Residual Stresses in Multi Hard Films Deposited by Arc Ion Plating

The present study investigates crystal orientations and residual stresses in multi hard layer films deposited by arc ion plating. TiN and CrN films approximately 1.0μm thick in single layer were deposited on a stainless steel substrate. With a bias voltage of 0V, the TiN film exhibited strong {110} texture, whereas the dominant orientation of the film deposited at –100V was {111}. On the other hand, CrN films exhibited strong {110} texture with a bias voltage of –100V. The crystal structure of double-layer film had the same tendency as those for single-layer films. TiN films had very high compressive residual stresses : –8.6GPa in the {110} textured film and –10.0GPa in the {111} textured film. These residual stresses decreased with increasing annealing temperature and the reduction rate was greater for the {111} than for the {110} film. The behavior of residual stresses in the {111} and {110} textured layers of {111}/{110} textured double-layer film was identical to that for single-layer films. The CrN films had very high compressive residual stresses of –8.4GPa. These residual stresses decreased with increasing annealing temperature. However, Annealing of temperatures at 600°C showed change in peak intensities of CrN 220 diffraction.

Thermal relaxation of residual stresses in TiN films deposited by arc ion plating

Abstract The present study investigates crystal orientations and residual stresses in TiN films deposited by arc ion plating. TiN films approximately 2.0 μm thick were deposited on a steel substrate. With a bias voltage of 0 V, the TiN film exhibited strong {110} texture, whereas the dominant orientation of the film deposited at −100V was {111}. TiN films had very high compressive residual stresses: −8.6 GPa in the {110} textured film and −10.0 GPa in the {111} textured film. These residual stresses decreased with increasing annealing temperature and the reduction rate was greater for the {111} than for the {100} film. The behavior of residual stresses in the {111} and {110} textured layers of {111}/{110} textured double-layer film was identical to that for single-layer films.

Effect of temperature on cyclic deformation behavior and residual stress relaxation of deep rolled under-aged aluminium alloy AA6110

Mechanical surface treatment (deep rolling) was performed at room temperature on the under-aged aluminium wrought alloy AA6110 (Al–Mg–Si–Cu). Afterwards, specimens were cyclically deformed at room and elevated temperatures up to 250 °C. The cyclic deformation behavior and s/n-curves of deep rolled under-aged AA6110 were investigated by stress-controlled fatigue tests and compared to the as-polished condition as a reference. The stability of residual stresses as well as diffraction peak broadening under high-loading and/or elevated-temperature conditions was investigated by X-ray diffraction methods before and after fatigue tests. Depth profiles of near-surface residual stresses as well as full width at half maximum (FWHM) values before and after fatigue tests at elevated temperatures are presented. Thermal residual stress relaxation of deep rolled under-aged AA6110 was investigated and analyzed by applying a Zener-Wert-Avrami function. Thermomechanical residual stress relaxation was analyzed through thermal residual stress relaxation and depth profiles of residual stresses before and after fatigue tests. Finally, an effective border line for the deep rolling treatment due to instability of near-surface work hardening was found and established in a stress amplitude–temperature diagram.

Influence of ageing on cyclic deformation behavior and residual stress relaxation of deep rolled as-quenched aluminium alloy AA6110

Deep rolling was applied to solution-heat-treated (as-quenched) AA6110 at room temperature. Subsequently, the deep rolled as-quenched specimens were aged at different temperatures and times. Push–pull fatigue tests were performed at room temperature to evaluate the optimized ageing condition. Cyclic deformation behavior, s/n-curves and depth profiles of near-surface residual stresses and full width at half maximum (FWHM) values of X-ray diffraction peaks as well as hardnesses are presented as compared to the conventional mechanical surface treatment (ageing followed by deep rolling). Thermal residual stress relaxation was investigated by applying a Zener–Wert–Avrami function. It was found that fatigue lifetimes of deep rolled as-quenched AA6110 after ageing were governed by near-surface hardness. Work- as well as precipitation hardening in near-surface regions enhances the fatigue lifetime significantly. Deep rolling after optimized ageing treatment can combine the work- and precipitation hardening in near surface regions and thus results in excellent fatigue strength of AA6110.

Residual stress relaxation of deep-rolled Al–Mg–Si–Cu alloy during cyclic loading at elevated temperatures

Near-surface macroscopic compressive residual stresses in a deep-rolled aluminium alloy AA6110-T6 (Al–Mg–Si–Cu) were measured during cyclic loading at elevated temperatures as a function of loading cycle. Thermal residual stress relaxation was investigated and analyzed by applying the Zener–Wert–Avrami function. The effects of stress amplitude as well as temperature on residual stress relaxation during stress-controlled cyclic loading at elevated temperatures were systematically investigated and analyzed using separate assessment of mechanical and thermal residual stress relaxation.

Thermal Residual Stress Relaxation in Powder Metal IN100 Superalloy

Abstract Relaxation of shot peen induced compressive residual stresses due to thermal exposure was measured using X-ray diffraction. The material used in this study was a hot isostatically pressed (HIP) powder metal (PM) IN100 nickel base superalloy. A total of 14 IN100 samples were shot peened to an Almen intensity of 6A using MI-170-R shot with 125 % coverage. The sample dimensions were nominally 16×13×4-mm thick with an irradiated X-ray region of 8×5 mm. Residual stress measurements were made at the surface and at nominal depths of 12, 25, 50, 75, 125, 175, 250, and 350 microns. The shot peened samples were thermal exposed at two temperatures (650, 704°C) and a range of exposure times (0.5–300 h). Residual stress measurements on shot peened samples without thermal exposure were used as a basis for comparison. The relaxation of shot peened compressive residual stresses under purely thermal loading was examined. The residual stresses exhibited an initial rapid decrease on the surface and in the depth at both temperatures. However, continued thermal exposure produced little or no change in surface residual stresses while peak compressive stresses in the depth continued to relax with time at both temperatures. In all cases of this study the retained peak compressive residual stress after thermal exposure was greater than 50 % of the baseline value.

Residual Stress Stability and Alternating Bending Strength of AISI 4140 after Shot Peening and Successive Annealing

Increases of residual stress stability and alternating bending strength of shot peened AISI 4140 are obtained by successive annealing treatments. This is caused by static strain aging effects, which lead to pinning of dislocations by carbon atoms and finest carbides. It will be shown that by short-time annealing of a quenched and tempered AISI 4140 it is possible to maximize the positive effect of static strain aging, while minimizing the detrimental effect of thermal residual stress relaxation, which was measured by X-ray diffraction method. Static strain aging effects were also found to be responsible for an increase of the quasi static and cyclic surface yield strengths.

Effects of static strain aging on residual stress stability and alternating bending strength of shot peened AISI 4140

Abstract Increases of residual stress stability and alternating bending strength of shot peened AISI 4140 are obtained by successive annealing treatments. This is caused by static strain aging effects, which lead to pinning of dislocations by carbon atoms and very small carbides. It will be shown that by well directed annealing of a quenched and tempered AISI 4140 it is possible to maximize the positive effects of statac strain aging, without causing extended thermal residual stress relaxation. The amount of yield stress increases caused by static strain aging is quantified using tensile tests. Static strain aging is also found to be responsible for an increase of the quasi static and cyclac surface yield strength present after shot peening.