Thermal Stress Relaxation Research Articles

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.

Relaxation of thermal mismatch stress due to plastic deformation in an Al/SiC p metal matrix composite

The neutron diffraction method was applied to determine the evolution of internal strains (and stresses) within an Al/SiC p metal matrix composite. The specimen was subjected to thermal treatment followed by different types of elastoplastic deformation. An Eshelby type model was used to study the contribution of different phenomena to the evolution of stress. The results of the experiment were compared with model predictions obtained using a self-consistent model of elastoplastic deformation. The validity of the use of this model for stress analysis was verified by comparison with a neutron diffraction measurement performed for an external load applied ‘in situ’. Hydrostatic phase stresses were experimentally found in the samples after thermal treatment. These stresses were modified due to plastic deformation, and significant relaxation of the microstresses was observed.

Specific Features of Changes in the Properties of One- and Two-Alkali Borate Glasses Containing Water: III. Thermal Expansion and the Structural and Mechanical Relaxation Parameters of Two-Alkali Borate Glasses

The thermal expansion and stress relaxation in mixed alkali borate glasses containing lithium, sodium, and potassium oxides with a total alkali oxide content of 15 mol % are measured on an inclined quartz dilatometer and a relaxometer. The experimental data obtained are used to determine the thermal expansion coefficients and the structural and mechanical relaxation parameters. No deviations from the additivity are found in the concentration dependences of the thermal expansion coefficient and the calculated parameters determining the width of the spectra of the structural and stress relaxation times. The IR absorption spectra of the studied glasses are recorded in the range of stretching vibrations of hydroxyl groups. Analysis of the IR spectra makes it possible to assume that the content of residual water in the structure of borate glasses affects the manifestation of the mixed alkali effect in the properties of these glasses.

Irreversing thermal expansivity of materials coated with adhesive thin films detected by modulated-temperature dilatometry and differential thermal analysis

Usability of simultaneous modulated-temperature dilatometry (MT DIL) and modulated-temperature differential thermal analysis (MT DTA) for the quantitative description of degradation kinetics of wear-resistant film adhesion to the substrate as a function of temperature are presented in this work. The reversing thermal expansion coefficient of materials as a parameter sensitive to the relaxation of mechanical thermal stresses in films tested was used for this purpose. Sample experimental results allowing the process of film degradation to be described as a function of increasing temperature are quoted. Usefulness of this method considering the films deposited at diversified process parameters is also substantiated.

Slit Structure as a Countermeasure for the Thermal Deformation of a Metal Mask

A metal mask used for the pattern formation of sputtered films is sometimes deformed during film deposition, because its temperature increases during deposition. In this study, a slit structure as a countermeasure for the deformation is proposed. The mask investigated is made of 0.3-mm-thick stainless steel and is composed of a frame with many beams running inside the frame. The slits in the structure absorb the thermal expansion of the beams, which results in the relaxation of thermal stress in the beams. The relaxation of the stress is analyzed using the finite element method as well as the theory of beam bending. It was experimentally confirmed that a mask furnished with well-designed slits was not deformed.

Thermal stresses and orientations in acrylic sheet

AbstractTwo copolymers of poly(methyl methacrylate) with 3% and 10% ethyl acrylate, respectively, were extruded and calendered, with the same line speed and roll temperatures. The residual stresses and anisotropies, induced by the complex processing deformations and temperature variations, were characterized by monitoring the dimensional changes and sample curvatures resulting from subsequent heat treatments. In both copolymers, two distinct recovery regimes were observed: heat treatments just below Tg caused relaxation of residual thermal stresses and at temperatures above Tg led to recovery of chain extended orientations. It was found that the similar processing conditions induced similar residual thermal stresses in the two copolymers, but the higher viscosity of the 3% EA sheet led to greater residual orientations. Across the width of the sheets, little variations were seen in the thermal stresses, but orientations were lower at the edges. Some curvature changes observed following heat treatment well below Tg, were interpreted as resulting from aging effects.

A finite-element analysis of the inelastic relaxation of thermal residual stress in continuous-fiber-reinforced composites

In an effort to develop a methodology for interpreting in situ high-temperature neutron diffraction measurements of thermal residual stresses in composites, a finite-element model was developed and the implications of various material and experimental parameters on the residual stress evolution were studied. The model composite comprised a continuous Al 2O 3 fiber, unidirectionally aligned in a NiAl matrix. The effects of temperature-dependent elastic, plastic or creep properties, fiber volume fraction and cooling/heating rates were explored on the relaxation mechanisms of the residual stress during an initial cooling and a subsequent heating. Thermal path-dependency in the stress evolution was investigated by comparing the cooling and re-heat cycles. The result shows that the effect of the time-dependent deformation (creep) becomes more significant as the fiber content increases and the cooling/heating rate decreases. Furthermore, the path-dependency in stress evolution becomes stronger (i.e. considering the actual thermal history in the model becomes more important) as the total inelastic relaxation increases during the cooling and/or the subsequent re-heating cycles due to; (i) the presence of creep in addition to plastic deformation, (ii) increased fiber volume fraction, and (iii) slower cooling/heating rates. It was also demonstrated that using an estimated stress-free temperature in elastic–plastic models can be problematic in predicting the high-temperature behavior due to; (i) the simple assumption of reduced Δ T, and (ii) the thermal path-dependency.

Transient Thermal Stresses in a Superelastic Shape Memory Alloy Strip.

The austenitic Shape Memory Alloy (SMA) can be loaded up to a large strain without any plastic deformation and behaves superelastically (pseudelastically) above its characteristic transition temperature. When loaded, the superelastic SMA undergoes a stress-induced martensitic transformation that will result in a large recoverable strain up to 8%. On unloading, the superelastic SMA experiences a large hysteresis loop that makes the alloy an useful candidate for strain energy absorption. By taking advantage of this effect, SMA is used in various fields. The SMA can be used to improve the impact damage tolerance of composite materials and to induce the relaxation of stress distribution. This investigation deals with the transient thermoelastic problem for a superelastic SMA strip under the heat exchange. In order to simplify the SMA model, a linearization of one dimensional constitutive equations is made. The piecewise linear stress-strain relation is separated into two parts : before and after the stress-induced martensitic phase transformation. Another assumption is the identical SMA stress-strain relation in tension and in compression. Results for the temperature and stresses distributions are obtained numerically. We discuss about the variation of the martensitic phase and the thermal stress relaxation.

Solid State Bonding of Graphite to Nickel

Graphite was bonded to nickel under joining compressive stress of 3 to 33 MPa in a vacuum at temperatures within the range of 973 to 1273 K using an RF-induction furnace. The influence of joining conditions on the bending strength of the graphite/nickel joint, and changes in the microstructure and hardness of nickel near the joining interface, were investigated. Thermal stress induced in the joint was estimated using the finite element method. On the basis of these results, the influence of thermal stress on the bending strength of the joint was examined Completion of the graphite/nickel joint depends on both joining compressive stress and joining temperature. At high joining temperature, good solid-state bonding under relatively low joining compressive stress becomes feasible. Axisymmetric thermoelastic finite element analysis suggests that the maximum tensile thermal stress is induced at a distance of 0.64 mm from the joining interface on the surface of graphite anal is increased with increasing joining temperature. The position of fracture in a bending test corresponds approximately to that of the maximum tensile thermal stress. Part of the thermal stress in practical joints is relaxed and less than that calculated using the finite element method. The bending strength of the joint increases with decreasing residual tensile stress on the surface of graphite. Relaxation of the maximum tensile thermal stress depends on the amount of carbon which diffuse into nickel. This may be related to changes in plasticity of both nickel and graphite, that is, changes in the amount of carbon that dissolves in nickel to supersaturation and the point defects introduced in graphite.

K-0612 回転円板の熱応力緩和を目指した最適熱伝達率分布の遺伝的アルゴリズムによる探索(S05-4 複合材料システムの弾性数理モデリング(4))(S05 複合材料システムの弾性数理モデリング)

An optimized heat-transfer coefficient distribution from the point of the relaxation of Mises equivalent thermal stress in a rotating disk subjected to local heat generation near the outer boundary and with arbitrary variations in heat-transfer coefficient along the radial position on the upper and lower surfaces of the disk, is proposed based on the analytical solutions to same heat conduction and thermal stress problems derived by the same authors and by using genetic algorithm.

103 傾斜機能材料からなる変厚回転円板の熱応力緩和最適設計(材料力学I)

103 傾斜機能材料からなる変厚回転円板の熱応力緩和最適設計(材料力学I)

Micromechanical Analysis of Inelastic Thermal Stress Relaxation in a Functionally Graded Laminate. Effects of Graded Compositional Distributions and Number of Layers.

In this paper, transient thermal stresses in an Al2O3-Ni functionally graded material (FGM) plate subjected to through-thickness heat flow have been numerically analyzed under three different mechanical boundary conditions by taking account of time dependent inelastic deformation due to interfacial diffusion between ceramic and metal phases as well as creep of both phases. First, an outline of the analytical method, which consists of micromechanical and macromechanical approaches, is briefly represented. The micromechanical approach stems from Eshelby's equivalent inclusion method and Mori-Tanaka's mean-field approximation, and the macromechanical one is based on the classical laminated plate theory. Second, we have systematically examined the effects of graded compositional distributions and the number of layers on the thermal stresses in the FGM plate in detail.

Mechanical spectroscopy of thermal stress relaxation at metal–ceramic interfaces in Aluminium-based composites

The micromechanisms of thermal stress relaxation in aluminum-based metal-matrix composites (MMCs) have been investigated by mechanical loss and dynamic shear modulus measurements during thermal cycling between 100 and 500 K. A transient mechanical loss maximum, which is absent in the monolithic material, appears during cooling. This damping maximum is strongly dependent on the measurement parameters: oscillation frequency, oscillation amplitude and cooling rate. In addition, it increases with the volumetric reinforcement content and decreases if the matrix strength is improved. The shear modulus evolution during thermal cycling shows that no detectable interfacial debonding occurs. Compared with alloyed MMCs, Al4N-based MMCs show the highest damping maximum simultaneously with a plateau in the elastic shear modulus. The mechanical loss maximum is attributed to dislocation generation and motion near the interfaces, resulting from the differential thermal contraction of matrix and reinforcement. A new model is proposed which describes this specific mechanical behavior of MMCs in terms of the development of microplastic zones in the matrix near the metal–ceramic interfaces.

Production of preset quality large Na(I)(Tl) single crystals for detectors used in medical instrument building

This study considers bending of the (001) planes perpendicular to the growth axis, as a result of thermal stress relaxation in the process of single crystal growth of NaI in various temperature fields. The possibility of introducing lattice bending of different signs was experimentally confirmed, for the first time, on NaI(Tl) single crystals. For the example of NaI(Tl) single crystals, 500 mm in diameter and up to 0.5 ton by weight, the possibility is shown of controlling the integral parameter of the structural perfection-bending of (001) crystallographic planes at an axial temperature gradient of 10–15° cm −1.

355 傾斜機能材料を中間層とする複合中空半球の熱応力緩和と GA による組成最適化

355 傾斜機能材料を中間層とする複合中空半球の熱応力緩和と GA による組成最適化

618 傾斜機能材料の製造時の熱応力緩和解析 : 相変態に適した冷却過程

618 傾斜機能材料の製造時の熱応力緩和解析 : 相変態に適した冷却過程

Combustion Synthesis and Thermal Stress Analysis of TiC–Ni Functionally Graded Materials

Simultaneous combustion synthesis reaction and compaction of Ti, C, and Ni powders under a hydrostatic pressure was carried out to fabricate dense TiC–Ni functionally graded materials (FGMs) in a single processing operation. Scanning-electron microscope (SEM) and microprobe analysis (EPMA) was employed to investigate the microstructure and composition distribution. Experimental results demonstrate that Ni and Ti composition varies continuously and gradually along the thickness of the reacted sample, remarkably different from stepwise type prior to combustion synthesis. The constituents are continuous in microstructure everywhere and no distinct interaction occurs in TiC–Ni FGM. Moreover, the thermal physical and mechanical properties were measured as a function of composition. It was found that the properties of the FGMs were dependent on Ni content. The residual thermal stress of TiC–Ni FGM and dual-laminate non-FGM cooled to room temperature after combustion synthesis has been analyzed by finite element method. TiC–Ni FGM shows distortion and thermal stress relaxation, which is in striking contrast to the layered TiC–Ni non-FGM.

黒鉛とニッケルの固相接合

Graphite was bonded to Ni under a compressive stress range from 3 to 33 MPa in a vacuum over a temperature range from 973 to 1273 K using a RF-induction furnace. The influence of joining conditions on the bending strength of the graphite/Ni joint, and changes of microstructure and hardness near the joining interface of Ni, were investigated. Thermal stress induced in the joint was estimated with a finite element method. On the basis of these results the influence of thermal stress on the bending strength of the joint as examined.Completion of the graphite/Ni joint depends on both the compressive stress and the joining temperature. Good solid state bonding becomes feasible under low compressive stress in case of higher joining temperatures. Axisymmetric thermoelastic finite element analysis suggests that maximum tensile thermal stress is induced at a distance of 0.64 mm from the joining interface on the surface of the graphite and is increased with increasing joining temperatures. The position of fracture in a bending test corresponds approximately to that of the maximum tensile thermal stress. A part of the thermal stress in practical joints is relaxed and less than that calculated by finite element method. The bending strength of the joint increases with decreasing residual tensile stress on the surface of graphite. Relaxation of maximum tensile thermal stress depends on the amount of carbon atoms which diffuse into Ni. This may be related to the changes in plasticity of Ni and graphite, that is, the changes in the amounts of C super-saturately dissolved in Ni and the point defects introduces in graphite.

Modeling Effects of Material Properties and Three-Dimensional Surface Roughness on Thermal Barrier Coatings

ABSTRACTThermal barrier coatings (TBCs) are known to spall as a result of the residual stresses that develop during thermal cycling. TBC's are multi-layered coatings comprised of a metallic bond coat, thermally grown oxide and the ceramic top coat, all on top of a Ni-base superalloy substrate. The development of residual stresses is related to the generation of thermal, elastic and plastic strains in each of the layers. The focus of the current study is the development of a finite element analysis (FEA) that will model the development of residual stresses in these layers. Both interfacial roughness and material parameters (e.g., modulus of elasticity, coefficient of thermal expansion and stress relaxation of the bond coat) play a significant role in the development of residual stresses. The FEA developed in this work incorporates both of these effects and will be used to study the consequence of interface roughness, as measured in SEM micrographs, and material properties, that are being measured in a parallel project, on the development of these stresses. In this paper, the effect of an idealized three-dimensional surface roughness is compared to residual stresses resulting from a grooved surface formed by revolving a sinusoidal wave about an axis of symmetry. It is shown that cylindrical and flat button models give similar results, while the 3-D model results in stresses that are significantly larger than the stresses predicted in 2-D.