Changes In Residual Stress Research Articles

Residual stress change with time of a segmented-in-series solid oxide fuel cell using an in situ X-ray stress measuring method

The changes with time of the residual stress on the electrolyte were measured in situ during re-oxidation under solid oxide fuel cell (SOFC) operation conditions using a segmented-in-series (SIS)-type SOFC and a conventional anode-supported planar (ASP)-type SOFC to understand the mechanical behaviour of the materials in the SOFC. In situ X-ray residual stress measurement was successful, and the real-time change with time of the residual stress of the electrolyte was revealed under SOFC operating conditions. In the ASP-type SOFC, the residual stress changed from compression to tensile stress, and destruction of the cell was confirmed 20 min after the air introduction. In contrast, in the case of the SIS-type SOFC, the residual stress was almost constant, even when the anode material was exposed to oxidation conditions for more than 4 h. These results indicate that the SIS-type SOFC has a high tolerance against reduction and oxidation (redox) compared with the ASP-type SOFC, which requires a conductive support material with a high Ni content. This is because the SIS-type SOFC has an electrically insulated support material that does not require a high Ni content.

Dependence of structural, optical and electrical properties on substrate temperature for hexagonal MgxZn1−xO films

Single hexagonal-phase MgxZn1−xO films were deposited on glass substrates by pulsed laser deposition from a ZnO target mixed with MgO. The effect of substrate temperature on the structural, electrical and optical properties was investigated by X-ray diffraction and the transmittance measurements. It was observed that Mg incorporation lead to a clear shift of the (002) peak position to lower angle with reference to pure ZnO films due to the residual stress change with deposition temperature. It was also found that Mg doping increased the resistivity by 2 orders of magnitude and the maximum resistivity was 0.072 Ω·cm at 550 °C with the carrier concentration of 1.1 × 1019 cm−3. The visible transmittance of above 80 % was obtain in the alloy films, which optical band gap was observed to increase with the substrate temperature, attaining 3.85 eV at 600 °C. The possible mechanism was discussed.

Effect of short-term tempering on microstructure and mechanical properties of high-strength FeCrMoVC

The present work describes a systematic investigation of the influence of short-term tempering on the microstructure and mechanical properties of a fast solidified Fe84.3Cr4.3Mo4.6V2.2C4.6 (at.%) alloy. The applied casting conditions promote the formation of non-equilibrium phases such as martensite, retained austenite and a complex network of fine carbides already in the as-cast state. Additional short-term tempering further increases the strength and hardness of the alloy along with significantly improved ductility under compressive and tensile loading. By this procedure an extremely high ultimate compression strength of almost 4500MPa combined with a compressive fracture strain of ∼22% and an ultimate tensile strength of over 1600MPa can be achieved. The interacting mechanisms appearing due to short-term tempering were investigated by different X-ray diffraction methods and Auger electron spectroscopy, and a transformation of austenite into martensite as well as the formation of nano-carbides and a change in residual stresses during tempering was detected. Altogether, the outstanding properties of the material combined with the energy-efficient manufacturing process for Fe84.3Cr4.3Mo4.6V2.2C4.6 open up a new possibility to obtain a high-strength and simultaneously adequately ductile alloy for advanced tool design.

Numerical simulation of welding temperature field, residual stress and deformation induced by electro slag welding

To increase productivity, welding process with large heat input such as electro slag welding (ESW) process has been used to connect the joints between the diaphragm and the column plate in high-rise steel building. However, the heat input of ESW is much higher than those of the other welding processes, and the high heat input not only largely alters the properties of steel but also results in large residual stresses. Consequently, the changes of steel properties and residual stresses induced by ESW have significantly effects on the safety of a structure. In this study, a three dimension (3-D) finite element model with considering moving heat source was developed to simulate the welding temperature field, Δt8/5 time, welding residual stress and distortion in a typical thick plate joint performed by ESW. The thermal cycles computed by finite element model were compared with experimental measurements. Meanwhile, the features of welding residual stress and distortion distributions in the ESW joint were investigated numerically. In addition, the influences of heat input on the size of heat affected-zone (HAZ), Δt8/5 time welding residual stress and distortion were examined. The thermal cycle curve and simulated by FEM model can be used to deduce the micro-structure as well as toughness of weld zone and HAZ, while the welding residual stress distribution estimated by numerical model can be helpful to assess the structural integrity.

Study of the high temperature oxidation performance of Thermal Barrier Coatings with HVOF sprayed bond coat and incorporating a PVD ceramic interlayer

The performance of an intermediate Cr3C2 ceramic layer applied by PVD between the bond coat and the ceramic top coat in a TBC system was evaluated. The thickness of the transitional layer was kept around 1–2μm. Two substrate materials and two distinct bond coats were combined in the tests. High Velocity Oxygen Fuel (HVOF) and Atmospheric Plasma Spraying (APS) were used respectively for bond coat and top coat deposition. Isothermal oxidation tests were performed at 1000°C in static air atmosphere. Thermal grown oxide (TGO) was measured and correlated to the exposition times. Results are discussed in terms of the TGO growth rate and changes in residual stresses. The results suggest an improvement in the oxidation resistance of the bond coat because of the presence of the intermediate layer.

Dynamics Simulation Analysis with Crankshaft Filled Rolling Based on ANSYS

With the platform of ANSYS finite element software, on the base of optimal residual stress theory established a crankshaft fillet rolling model under conditions of kinetic analysis and conducted a simulation test. The dynamic changes of residual stress and effective stress are given by different amounts of feed rate and the rolling pass,and comes to the conclusion that 480Q crankshaft when rolling at the depth of 0.66mm the effective rolling stress is the largest, residual stress will increase in the plastic deformation process,for the enhanced production of the actual crankshaft rolling provides quantitative guidance.

Effect of deposition conditions on thermo-mechanical properties of free standing silicon-rich silicon nitride thin film

Even small differences in gas composition in low pressure CVD deposition make substantial changes in residual stress and significant but smaller changes in the elastic modulus and thermal expansion coefficient of silicon-rich silicon nitride thin films. ► An investigation on the mechanical properties of the SiN x thin film was performed. ► The elastic modulus linearly depends on SiCl 2 H 2 /NH 3 gaseous ratio. ► Thermal expansion coefficient of the SiN x thin film for each SiCl 2 H 2 /NH 3 gaseous ratio was obtained. ► The SiCl 2 H 2 /NH 3 gaseous ratio has also an effect on the residual stress of each sample. Using resonance and bulge techniques, the mechanical properties of free standing Si-rich SiN x membranes were precisely measured to evaluate the effect of deposition conditions on them over a narrow range of particular technological interest. Values of the elastic modulus, the residual stress and the thermal expansion coefficient were obtained. It was found that even small differences in gas composition in low pressure CVD deposition make substantial changes in residual stress and significant but much smaller changes in the elastic modulus.

Lateral gradients of phases, residual stress and hardness in a laser heated Ti0.52Al0.48N coating on hard metal

The influence of a local thermal treatment on the properties of Ti–Al–N coatings is not understood. In the present work, a Ti0.52Al0.48N coating on a WC–Co substrate was heated with a diode laser up to 900°C for 30s and radially symmetric lateral gradients of phases, residual stress and hardness were characterized ex-situ using position-resolved synchrotron X-ray diffraction, Raman spectroscopy, transmission electron microscopy and nanoindentation. The results reveal (i) a residual stress relaxation at the edge of the irradiated area and (ii) a compressive stress increase of few GPa in the irradiated area center due to the Ti–Al–N decomposition, in particular due to the formation of small wurtzite (w) AlN domains. The coating hardness increased from 35 to 47GPa towards the center of the heated spot. In the underlying heated substrate, a residual stress change from about −200 to 500MPa down to a depth of 6μm is observed. Complementary, in-situ high-temperature X-ray diffraction analysis of stresses in a homogeneously heated Ti0.52Al0.48N coating on a WC–Co substrate was performed in the range of 25–1003°C. The in-situ experiment revealed the origin of the observed thermally-activated residual stress oscillation across the laser heated spot. Finally, it is demonstrated that the coupling of laser heating to produce lateral thermal gradients and position-resolved experimental techniques opens the possibility to perform fast screening of structure–property relationships in complex materials.

헬리컬기어 제조공정에 따른 특성 비교 -단조품과 기계가공품-

Although high productivity is possible, cold forged helical gears have not been widely used due to difficulty in achieving mechanical properties as well as dimensional accuracy of the product. Confidence in the gear characteristics also is very important in heavy-duty gear applications. Therefore, the properties of forged gears must be compared to the properties of conventional machined gears. The properties might be different due to the different fabrication processes. In this study, machined and forged products both before and after heat-treated have been compared by measuring the residual stress and involute curve of the tooth. Characteristics of hardness and microstructure were also compared. Additionally, tooth fracture strength was compared for the heat-treated products. Moreover, the tooth strength and the fracture pattern were compared between the machined and forged gears. The forged gear showed decreased changes in residual stress and decreased changes in dimensions when compared to the machined gear before and after heat treatment. The forged gear was over 10% better than the machined gear in tooth strength.

The Change of Residual Stress with Two-Wire Spacing of Twin-Wire Submerged Arc Welding

Finite element software MSC.MARC was used to analyze the residual stress of high-strength low-alloy steel suffered twin-wire SAW. The numerical simulation of the residual stress field with different twin-wire spacing was conducted. The residual stress test results under twin-wire SAW at twin-wire of 50 mm welding were compared to the simulation results, which verified the numerical simulation. The results showed that in the single-channel and twin-wire welding, the largest welding residual stress of the joints is located near the weld toe. At certain wire distances (20-100 mm) in the twin-wire welding process, increasing distance only minimally reduces welding residual stress. Thus, the effects of residual stress on two-wire spacing have been neglected in studies on the twin-wire welding process,More studies should focus on the impact of the performance and forming of the weld joint.

OS0110 レーザ・ピーニング処理による改良9Cr-1Mo鋼の残留応力分布とクリープ寿命の変化

The present paper has investigated the effects of the laser peening treatment on the changes in residual stress, creep life and microstructure in modified 9Cr-1Mo steel. The X-ray diffraction analysis revealed that the peening treatment can change subsurface residual stress from tensile to compressive at an output laser power of 5.6〜22GW/cm^2. The creep life of the steel can be doubled by the peening treatment for σ=240MPa at 823 K in air. The EBSD/SEM analysis also revealed that laser treatment can coarsen crystal grains in the crept steel. This effect may have brought about longer creep life of the steel.

The Stress and Microstructure analysis of Polycrystalline Silicon Films Deposited by LPCVD

ABSTRACTAmorphous (a-Si) and polycrystalline silicon(c-Si) films have been obtained by low pressure chemical vapor deposition (LPCVD) in fixed silane flow at low pressure (200 mtorr) with variable growth temperature. Measurement of residual stress of polysilicon films growth between 570°C to 620°C was reported. Residual stress of polycrystalline silicon depends on film microstructure. The poly-silicon microstructure is a strong function of LPCVD growth temperature and pressure. In this work, Raman Scattering and X-ray diffraction (XRD) were used to study the film structure and composition. The multilayer optical model of Spectroscopic ellipsometry (SE) was used to crosscheck the crystallinity fraction. The surface roughness was identified by Atomic force microscopy (AFM) and SE. The residual stress changed from compressive to tensile and back to compressive for deposition temperature between 570°C and 620°C. Film’s c-Si fraction increased as a function of deposition temperature. The roughness surface was found at deposition temperature of 580°C. For deposition temperature larger then 580°C, all films shown (200) texture. The (220) grain size increased from 18.6 nm to 25 nm when deposition temperature increased from 580°C to 620°C. The film residual stress change can be explained by grain structure, surface stress and volume stress. At deposition temperature from 580°C to 587°C, grain is equi-axes type and volume stress dominate which cause the tensile stress. For temperature higher then 587°C inverse conical grain formed from oxide interface to surface and surface stress dominate cause the stress back to compressive. The columnar structure formed when deposition temperature > 600°C, grain growth push the compressive stress decrease again.

Investigation of laser shock peening effects on residual stress state and fatigue performance of titanium alloys

Abstract Laser shock peening can potentially enhance fatigue life of titanium components by inducing compressive residual stresses in surface layers much deeper than caused by traditional shot peening (SP). In the present study, the high cycle fatigue (HCF) performance of α Ti-alloy Ti–2.5Cu, (α + β) Ti-alloy TIMETAL 54M and the metastable β Ti-alloy TIMETAL LCB was investigated after laser shock peening without coating (LPwC). The fatigue results were interpreted by examining the changes of surface morphology, microhardness and residual stress generated in the surface layer. Furthermore, thermal stability of residual stresses in aged Ti–2.5Cu, as an example, was evaluated after annealing LPwC-treated material at various elevated temperatures and exposure times by applying a Zener–Wert–Avrami approach. The depth profiles of residual stresses were obtained by means of synchrotron X-ray diffraction or by incremental hole drilling method. Results revealed that the HCF performance of Ti–2.5Cu and TIMETAL LCB was markedly improved after LPwC, while it was deteriorated in TIMETAL 54M. Compared to LPwC, better 10 7 fatigue strength of Ti–2.5Cu was obtained after ball-burnishing (BB). Moreover, LPwC-induced residual stresses are thermally more stable than shot peening-induced ones.

Sensitivity analysis of bi-layered ceramic dental restorations

Objectives The reliability and longevity of ceramic prostheses have become a major concern. The existing studies have focused on some critical issues from clinical perspectives, but more researches are needed to address fundamental sciences and fabrication issues to ensure the longevity and durability of ceramic prostheses. The aim of this paper was to explore how “sensitive” the thermal and mechanical responses, in terms of changes in temperature and thermal residual stress of the bi-layered ceramic systems and crown models will be with respect to the perturbation of the design variables chosen (e.g. layer thickness and heat transfer coefficient) in a quantitative way. Methods In this study, three bi-layered ceramic models with different geometries are considered: (i) a simple bi-layered plate, (ii) a simple bi-layer triangle, and (iii) an axisymmetric bi-layered crown. Results The layer thickness and convective heat transfer coefficient (or cooling rate) seem to be more sensitive for the porcelain fused on zirconia substrate models. Significance The resultant sensitivities indicate a critical importance of the heat transfer coefficient and thickness ratio of core to veneer on the temperature distributions and residual stresses in each model. The findings provide a quantitative basis for assessing the effects of fabrication uncertainties and optimizing the design of ceramic prostheses.

Influence of deposition parameters on hard Cr–Al–N coatings deposited by multi-arc ion plating

The Cr–Al–N coatings were synthesized at various substrate bias voltages and nitrogen partial pressures by multi-arc ion plating (M-AIP). The relationships between deposition parameters and coating properties were investigated. Morphologies, phase structures, hardness and adhesion strength of the coatings were analyzed by SEM, XRD, XPS, nano-indenter and scratch tester. The results indicated that with the increase of substrate bias voltages, the surface macroparticles and deposition rate reduced mainly for the resputtering phenomenon. The (Cr, Al)N solid-solution phase kept unchanged, but the Cr2N and AlN phases disappeared gradually. Due to the change of phase structures and residual compressive stress, the hardness values decreased and the adhesion strength decreased initially and then increased. Similarly, with the increase of nitrogen partial pressures, the phase structures of CrAlN coatings varied from Cr+Cr2N+(Cr,Al)N to Cr2N+(Cr,Al)N. The surface macroparticles increased due to the decreasing resputtering efficiency, and the deposition rate increased initially and then decreased due to the resputtering phenomenon. With increasing nitrogen partial pressures, adhesion strength decreased initially and then increased. The microhardness increased mainly due to the increase of Cr2N contents and decrease of metal macroparticles.

Surface Integrity in Notches Machining

Precision machining of soft and hardened materials is a topic of high interest to substitute some traditional operations. This paper deals with some aspects of the precision machining of notches. All machining processes result in changes of surface layer properties. There are changes in residual stresses, in harness, changes in material structure etc. and also in surface accuracy and surface roughness. All these characteristics may affect fatigue cracks in machined parts.

Effect of Crystallization Process at Cryogenic Conditions on the Functional Properties of the SUPERSTON Alloy Used in Production the Ship’s Propellers

The purpose of this paper is to show results of laser treatment at cryogenic conditions of the SUPERSTON alloy used for ship’s propellers. That modification process ought to bring beneficial changes of microstructure and residual stresses in the surface layer. During the laser remelting at cryogenic conditions the microstructure changes significantly. This is related to synergistic effects of the solidification rate, phase transformations in the solid state and laser treatment parameters. That crystallization process had influence on functional properties such as corrosion and cavitation resistance of the SUPERSTON alloy which were tested during researches.

Changes in the axial residual stresses in AISI 1045 steel bars resulting from a combined drawing process chain

The present paper investigates the redistribution of residual stresses resulting from manufacturing steps in the production of cold-drawn AISI 1045 steel bars. The main steps in this process chain are the pre-straightening of coiled material, shot-blasting, cold-drawing, cutting, and final straightening with crossed rolls. Drawing and final straightening parameters were changed to evaluate their influence on the residual stress distributions as measured by X-ray diffraction and hole-drilling techniques after the different manufacturing steps. It was found that, depending on the manufacturing parameters, the pre-straightened material generates non-homogeneity of residual stresses which can remain even after the last manufacturing steps. The angle between the crossed rolls in the final straightening has a high influence on the homogeneity of the surface residual stresses. Both the drawing angle and the angle between the crossed rolls significantly affect the residual stress depth distribution.

Nanoscale planar faulting in nanocrystalline Ni–W thin films: Grain growth, segregation, and residual stress

Abstract

The Magnitude and Origin of Residual Stress in Ti-6Al-4V Linear Friction Welds: An Investigation by Validated Numerical Modeling

The linear friction welding (LFW) process—of the type required for production of bladed discs for the next-generation aeroengines—was modeled using numerical methods developed previously. An elastic–viscoplastic material formulation was considered to allow for residual stress calculations to be included in the numerical solution. A study of the evolution of residual stress during the welding and cooling processes was made. It was evident that residual stresses arose primarily as a consequence of the cooling of the part after joining is completed. The sensitivity of predicted residual stress to the applied forge load was investigated and compared with measurements from X-ray diffraction methods. Only small changes in residual stress were predicted for large changes in forge load, supporting the hypothesis that the welding process is only of secondary importance to residual stress formation, after the cooling process. Finally, a sensitivity study was carried out investigating the accuracy of modeling the welding process with a simpler, viscoplastic material law, and only switching to the more computationally demanding elastic–viscoplastic law for the cooling modeling. Predictions suggested that this was a sufficient modeling method, given that stress during the welding stage is almost uncorrelated to that present once ambient temperature is reached.