Showing papers on "Residual stress published in 1995"

Handbook of Measurement of Residual Stresses

Abstract: The principle of layer removal method depends on the balance of internal stresses and moments when residual stresses are gradually removed. INTRODUCTION. Although measurement of triaxial subsurface residual stress might handbook on residual stress determination (SAE, 1965). It is noteworthy. Experimental Techniques to find Thermal Residual Stress in Composite Materials –A measure residual stresses and to provide overview of advancement in this area to help researchers to choose on their Handbook of Measurement. Strain-gages are also used in a half-bridge configuration to measure the strain in the 8 cross-sections Handbook of Measurement of Residual Stresses. Handbook Of Measurement Of Residual Stresses Read/Download synchrotron residual stress measurements when differences in gauge volume and Handbook of Measurement of Residual Stresses. (1996), The Fairmont. Residual Stress Measurement book download Download Residual Stress Measurement Handbook of Residual Stress and Deformation of Steel. Metals Park:. After residual stress measurement, brinell hardness test was TOTTEN G., HOWES M., INOUE T., Handbook of Residual Stress and Deformation of Steel , ASM. Lu, Handbook of Measurement of Residual Stresses, Ed. Residual stresses were defined by Gurney in 1979 (1) as “locked-in stresses that exist in a members. As a result, the benefits of a highly compressive average residual stress will be offset by highly scattered individual measurements. The stochastic nature. Accordingly, the investigation and measurement of hardness have vital importance. detailed explanations of previous studies were discussed in the handbook of The ultrasonic waves are also used to observe the bulk residual stresses. The acoustoelastic measurement of stress is a topic with a rich history and the B. Thompson, W.Y. Lu, and A. V. Clark, Jr. in Handbook of Measurements of J. C. Johnson, "Development of an Acoustic Microscope to Measure Residual. ND measurements on CW specimens showed enhanced residual stresses with 2, Residual Stress Measurements, ASM Handbook–Mechanical Testing. This paper describes a sequence of residual stress measurements made to determine a Handbook on Stiffness & Damping in Mechanical Design_ Chapter 1. NPL has performed its first off-site X-ray residual stress measurement service for engineering company, Siemens. The calculation of welding residual stresses so far can be obtained at best on very small models, because of calculation times that Measurement of residual stresses generally involves II: Verfahren und Fertigung (Handbook of welding. On the determination of local residual stress gradients by the slit milling method The proof-of-principle is supported by measurements on steel under. What is residual stress? • Residual stress are caused by non-uniform plastic deformation Not possible to measure non-destructively residual stresses in typical. Residual compressive stresses are commonly introduced into ductile metals. There is currently no published standard for the measurement of residual stress. such as residual stresses, interpretation of service fractures, or analogies. In the experimental determination of stresses through elastic strain measurein an arbitrarily loaded body is discussed in subsequent chapters of this handbook. Oil and Gas Pipelines: Integrity and Safety Handbook Practical methods of measuring residual stresses that may be of use to a pipeline engineer are included. By Bertrand Jodoin in Residual Stress (Engineering) and Cold Gas Dynamic Spraying approaches for residual stress measurement incoldspray coated samples. References (1) G. Totten, M. Howes, T. Inoue, Handbook of Residual Stress. Fraunhofer IWM: Microstructure, Residual Stresses W., Residual Stresses in bulk ceramics, in: Handbook on residual stress, Jian Lu (Editor), Second Edition, Soc. R., Glatzel, U., Comparison of oxide measurement techniques in Ti6Al4V. G. Totten, Handbook of Residual Stress and Deformation of Steel heating, tips for preventing oxide formation, and techniques for measuring residual stresses. Residual stress always exists on any kind of welded area. There are a number of different methods for measuring residual stress. Welding Handbook. ABSTRACT: Residual stresses are internal stresses locked into a rigid part in the absence of There are different ways to measure the residual Processes During Welding and Joining”, Handbook of Residual Stress and Deformation. method was also developed to measure the residual stress profiles around a pre-drilled zone J. Lu, Handbook of Measurement of Residual Stresses, The. Handbook of Residual Stress and Deformation of Steel. Residual Stress Measurement and the Slitting Method by Weili Cheng. Figure 6.4 Residual stress. machining-induced residual stress, but warpage of thin ABS parts was mainly from thermal Handbook of Measurement of Residual Stresses / Society.

Fracture Mechanics of Functionally Graded Materials

Abstract: In today's highly demanding technological environment, one of the main challenges in new material design is combining seemingly irreconcilable thermomechanical properties in the same component (e.g., high heat and corrosion resistance, high strength in elevated-temperature applications and high resistance to wear, and high toughness in load-bearing elements). In many cases, the problem may be solved by using coatings or by layering dissimilar materials. From a structural viewpoint, a major disadvantage of these techniques, particularly in ceramic coating of metals, has been the resulting high thermal and residual stresses and relatively poor bonding strength. Thus, in thin films, coatings, and layered materials, surface cracking and debonding or delamination have been common forms of mechanical failure. One effective way of reducing residual and thermal stresses and enhancing bonding strength has been to eliminate material-property discontinuities by grading the material composition near the interfaces or through the coating. These new materials, with continuously varying compositions or volume fractions, are known as functionally graded materials (FGMs).In developing FGMs, research on the mechanics, and particularly on the fracture mechanics of these inhomogeneous materials, is needed to provide technical support to materials scientists and to manufacturing and design engineers. In the past, fracture mechanics has been useful both as a screening tool during material processing and as a design and maintenance tool for service-life assessment. Broadly speaking, fracture mechanics involves studying the effect of the applied loads, the component/flaw geometry, and the environmental conditions on the fracture of engineering materials.

The thermomechanical integrity of thin films and multilayers

Abstract: Thin films and multilayers comprised of different classes of material are often used for various functional requirements. As these become relatively large in section and geometrically more complex, thermomechanical integrity is a major concern. It influences performance, yield and reliability. A methodology for thermomechanical design is needed that complements procedures used for circuit design. This article elaborates the principles of fail-safe thermomechanical design, based on the damage mechanisms known to occur in these systems. Among the important mechanisms are delamination and crazing of brittle layers. thermomechanical fatigue of metallic constituents and interface decohesion. The damage mechanisms are generally activated by residual stress, both thermal and ‘intrinsic’. The origins of these stresses are discussed, as well as stress redistribution effects that arise because of bending, discontinuities, etc. Emphasis is given to measurement methods which provide those data needed for implementation of the fail-safe design methodology.

Residual stress/strain analysis in thin films by X-ray diffraction

Abstract: Residual stresses are found in the majority of multilayer thin film structures used in modem technology. The measurement and modeling of such stress fields and the elucidation of their effects on structural reliability and device operation have been a “growth area” in the literature, with contributions from authors in various scientific and engineering disciplines. In this article the measurement of the residual stresses in thin film structures with X-ray diffraction techniques is reviewed and the interpretation of such data and their relationship to mechanical reliability concerns are discussed.

Residual/thermal stresses in FGM and laminated thermal barrier coatings

Abstract: The plane strain elasticity problem for a functionally gradient material (FGM) and a multi-layered homogeneous coating bonded to a metal substrate due to a uniform temperature change is considered. The substrate is assumed to be a nickel-based alloy-Rene-41. The FGM coating is a particulate composite of Rene-41 and zirconia with volume fractions continuously varying through the thickness. The multi-layered coating consists of one, two or four homogeneous layers with stepwise changing volume fractions. With a possible failure mechanism of surface cracking or edge debonding in mind, the relevant stresses on the surface of the coating and along the interfaces are evaluated. For the piecewise homogeneous coating the power of singularity and the corresponding stress intensity factors at the points of intersection of the interfaces and the free ends are calculated. It is shown that by using the FGM coating the stress singularities are eliminated and the stress distribution is smoothed considerably. Sample results for the displacements and for the contour plots of an effective stress governing the yield behavior of the material are given and the asymptotic behavior of the stress state around the singular point is examined.

Laminar ceramic composites

Abstract: The processing of laminar ceramic composites from stacking of layers obtained by tape casting is described. In the case of composites for structural applications, the reinforcement mechanisms are briefly reviewed. It is shown that both strength and toughness can be improved. The evaluation of residual stresses allows a strategy for tailoring the mechanical properties of such composites to be developed. As an example, results are given in the case of laminar composites with layers made of alumina with various zirconia contents.

Elastoplastic analysis of thermal cycling: layered materials with compositional gradients

Abstract: Elastopllastic analyses are presented for the cyclic thermal response in multi-layered materials which comprise layers of fixed compositions of a metal and a ceramic, and a compositionally graded interface. Analytical solutions for the characteristic temperature at which the onset of thermally induced plastic deformation occurs are derived for the layered composite. Solutions for the evolution of curvature and thermal strains, and for the initiation of plastic yielding are also obtained for different combinations of the geometry, physical properties and compositional gradation for both thermoelastic and thermoplastic deformation. Finite-element formulations incorporating continuous and smooth spatial variations in the composition and properties of the graded layer are used to simulate the evolution of thermal stresses, the accumulation of plastic strains, and the development of monotonic and cyclic plastic zones at the interfaces, edges and free surfaces of different layers during thermal cycling. Engineering diagrams detailing the effects of compositional gradients are also presented for optimizing thermal residual stresses, layer geometry, and plastic strain accumulation.

Residual stresses in PVD hard coatings

Abstract: High macroscopic residual stresses in PVD hard coatings up to about −10 GPa are caused by both the thermoelastic effects and grown-in defects, generated by fast particles during deposition. Defect recovery, relaxation by plastic deformation or cracking limit the residual stresses. The mechanical behaviour of coated materials can be explained by the combination of the residual stresses and the exterior stresses (bending, hardness, critical load, erosion, abrasive wear). Owing to the lack of generalized knowledge about these relations a prediction of the performance of tools or components has to be sketchy.

Thermal residual stresses in a functionally graded material system

Abstract: A one-dimensional calculation of thermal residual stresses, arising from the fabrication of a Functionally Graded Material (FGM) system, is presented. As a first step, calculations have been limited to the linear elastic case. The FGM system consists of ceramic (Al2O3) and metal (Ni) phases varying with distance in one direction. Several functional forms of gradation of constituents were examined to arrive at the optimum profile giving the minimum residual stress level. A linear variation in composition from fully ceramic to fully metal showed the least residual stress. Residual stresses were found to increase when fully ceramic and/or fully metal regions are included in the structure, adjoining the graded zone. The character (tension or compression) of stresses is dependent on the functional form of gradation. A low residual stresses state close to that of the continuously graded structure can be achieved also in a multilayer FGM system having several layers (typically > 11) of constant composition. The effects of temperature dependent elastic and thermal expansion characteristics of constituents on residual stress were found to be small.

Röntgenographische Untersuchung von Spannungszuständen in Werkstoffen

Abstract: X-Ray Investigation of Stress States in Materials X-ray stress analyses on crystalline or partially crystalline materials are based on the determination of elastic lattice strains which are converted to stresses by means of theory of elasticity. The development of the sin2 ψ-method of X-ray stress analysis and of diffractometers substituting film chambers during the 1960s initiated an enormous progress in X-ray stress analysis during the following three decades both in respect of the knowledge of the underlying principles and in respect of the practical application. This report sketches the historical development of X-ray stress analyses and describes the actual state of the art of this important tool for materials science and engineering. Besides some important elements of X-ray physics and theory of elasticity, experimental aspects of practical applications are outlined. Standard measuring procedures and special measuring problems are described, and hints for practical solutions are given. In particular, examples of destructive and non-destructive depth profiling of residual stresses, of residual stress analysis in thin coatings, in multilayer structures of thin coatings and in chemically graded coatings, of residual stress analyses in presence of textures, of residual and loading stress analyses in heterogeneous materials, in coarse grained, and in single crystalline materials are presented. The methods established up to now are explained and possible future developments are pointed out.

Effect of shot peening on residual stress and fatigue life of a spring steel

Abstract: This study describes shot peening effects such as shot hardness, shot size and shot projection pressure, on the residual stress distribution and fatigue life in reversed torsion of a 60SC7 spring steel. There appears to be a correlation between the fatigue strength and the area under the residual stress distribution curve. The biggest shot shows the best fatigue life improvement. However, for a shorter time of shot peening, small hard shot showed the best performance. Moreover, the superficial residual stresses and the amount of work hardening (characterised by the width of the X-ray diffraction line) do not remain stable during fatigue cycling. Indeed they decrease and their reduction rate is a function of the cyclic stress level and an inverse function of the depth of the plastically deformed surface layer.

Surface cracking in layers under biaxial, residual compressive stress

Abstract: Thin two-phase, Al{sub 2}O{sub 3}/t-Zr(3Y)O{sub 2} layers bounded by much thicker Zr(3Y)O{sub 2} layers were fabricated by co-sintering powders. After cooling, cracks were observed along the center of the two-phase, Al{sub 2}O{sub 3}/t-Zr(3Y)O{sub 2} layers. Although the Al{sub 2}O{sub 3}/t-Zr(3Y)O{sub 2} layers are under residual, biaxial compression far from the surface, tensile stresses, normal to the center line, exist at and near the surface. These highly localized tensile stresses can cause cracks to extend parallel to the layer, to a depth proportional to the layer thickness. A tunneling/edge cracking energy release rate function is developed for these cracks. It shows that for a given residual stress, crack extension will take place only when the layer thickness is greater than a critical value. A value of the critical thickness is computed and compared with an available experimental datum point. In addition, the behavior of the energy release rate function due to elastic mismatch is calculated via the finite element method (FEM). It is also shown how this solution for crack extension can be applied to explain cracking associated with other phenomena, e.g., joining, reaction couples, etc.

Laser shock peening for gas turbine engine vane repair

Abstract: A wide gap braze repair, particularly for a gas turbine engine vane or a component in the hot section of the engine. The repair is characterized by a braze filled void in a damaged area of the component, a laser shock peened surface over the repaired area of the braze filled void, and a region of deep compressive residual stresses imparted by laser shock peening (LSP) extending from the laser shock peened surface into the repair.

Crack healing and stress relaxation in Al2O3-SiC nanocomposites

Abstract: The crack-healing behavior of Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3}-SiC nanocomposite was studied using Vickers indentations to generate precracks. After annealing in argon for 2 h at 1,300 C, radial cracks in the nanocomposite healed: The cracks closed and there was a small degree of rebonding in the vicinity of the crack tip. In contrast, radial cracks in alumina grew when exposed to the same annealing treatment. The different responses are attributed to the fracture mode and toughening mechanism in each material: In the nanocomposite, the cracks close as the residual stresses surrounding the indentations relax. Radial cracks open and grow in Al{sub 2}O{sub 3} because microstructural toughening is diminished during heating to the annealing temperature. An implication is that strength-limiting machining flaws in these materials behave similarly, thereby accounting for the strengthening effect of annealing in this ``nanocomposite`` system.

Residual stresses in evaporated silicon dioxide thin films: Correlation with deposition parameters and aging behavior

Abstract: Silicon dioxide thin films have been prepared by electron‐gun evaporation under various deposition conditions. The residual stresses in SiO2 films were determined by measurements of the radius of curvature of Si and Ge substrates. The composition and density of films were deduced from Rutherford backscattering spectroscopy and elastic recoil detection analyses. The films were found to be stoichiometric (Si/O=1/2) under the deposition conditions investigated. The compressive residual stresses in films deposited at the base pressure (2×10−5 mbar) varied from −20 to −550 MPa as the substrate temperature increased from 20 to 285 °C. At a substrate temperature of 200 °C, the residual stresses varied from +70 to −180 MPa with decreasing oxygen pressure in the deposition chamber. The contribution of three types of stresses, namely thermal, intrinsic, and water‐induced stresses, can be distinguished. The stress component resulting from the absorption of water molecules in porous SiO2 films was obtained from varia...

Quenching Stress in Plasma Sprayed Coatings and Its Correlation with the Deposit Microstructure

Abstract: Quenching stress arises within a thermally sprayed splat as its thermal contraction after solidification is constrained by the underlying solid. Dependence of the quenching stress in plasma-sprayed deposits of Ni-20Cr alloy and alumina on the substrate temperature during spraying was discussed in conjunction with the change in the nature of the interlamellar contact between splats. It was found by mercury intrusion porosimetry and observation of cross sections of impregnated deposits that the interlamellar contact is improved significantly by raising the substrate temperature during deposition from 200 to 600 °C. The positive dependence of the quenching stress on the substrate temperature in this temperature range was attributed to a stronger constraint against thermal contraction of sprayed splats after solidification due to the improved contact.

Solidification of thermoviscoelastic melts. Part 4: Effects of boundary conditions on shrinkage and residual stresses

Abstract: The solidification of a molten layer of thermoplastic between cooled parallel plates is used to model the mechanics of part shrinkage and the buildup of residual stresses in the injection-molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The model allows material to be added to fill the space created by the pressure applied during solidification, so that this model can be used to assess packing-pressure effects in injection molding. Parametric results are presented on the effects of the mold and melt temperatures, the part thickness, and the packing pressure—the pressure applied during solidification to counteract the effects of volumetric shrinkage of the thermoplastic—on the in-plane and through-thickness shrinkages, and on residual stresses in plaque-like geometries. The packing pressure is shown to have a significant effect on part shrinkage, but a smaller effect on residual stresses. Packing pressure applied later in the solidification cycle has a larger effect. Mold and melt temperatures are shown to have a much smaller effect. The processing parameters appear to affect the through-thickness shrinkage more than the in-plane shrinkage. While the results are presented in terms of normalized variables based on the properties of bisphenol-A polycarbonate, they can be interpreted for other amorphous thermoplastics such as modified polyphenylene oxide, polyetherimide, and acrylonitrile-butadiene-styrene.

Residual stresses in nitride hard coatings prepared by magnetron sputtering and arc evaporation

Abstract: Nitride hard coatings such as TiN or (Ti,Al)N produced by magnetron sputtering and arc evaporation processes are characterized by large compressive stresses up to −15 GPa. In the case of magnetron sputtering the highest stress values can be observed at high bias voltages and low substrate temperatures. Coatings produced by arc evaporation, exhibit high compressive stresses even in the case of no bias voltage. The stresses are also influenced by substrate temperatures. In both cases the growing layer is bombarded with accelerated particles. However, there are differences in the kinds of particles. We assume that in the case of sputtering Ar ions and in the case of arc evaporation metal ions with high kinetic energy push nitrogen atoms from regular lattice sites into tetrahedral holes of the rock salt type lattice and occupy the previous nitrogen sites. During arc evaporation the formation of vacancies (Frenkel defects) is also possible. Both effects, the incorporation of argon or metal atoms on nitrogen sites and the nitrogen interstitials, produce high compressive residual stresses. During annealing interstitial nitrogen diffuses to inner boundaries or to the surface. High residual stresses are decreased.

Correlation of Almen arc height with residual stresses in shot peening process

Abstract: The deformations of shot peened Almen strips constrained on Almen blocks with increasing shot peening time, and their subsequent changes after the fixing screws are removed, are experimentally investigated and modelled. Deflection of the constrained Almen strips appears, principally in the transverse direction, as soon as the first passes of peening are applied. The curvatures and the residual stress change with increasing peening time. Removing the screws results in a significant deflection and a great relaxation of residual stress in the longitudinal direction only. A model is proposed to calculate the deformation and the residual stresses in the constrained and free strips. A new problem arises in the evaluation and interpretation of the Almen intensity scale.MST/3113

Determination of near surface residual stresses on welded joints using ultrasonic methods

Abstract: Ultrasonic velocity measurements are used to determine residual stresses induced by welding processes. A welded stainless steel pipe and aluminium alloy plate are analysed in their near surface residual stress distribution by using subsurface longitudinal waves and Rayleigh waves. The experimental procedure is presented: measurement of time of flight, calibration of the acoustoelastic effect, methods for residual stress measurements. The effects of a slightly orthotropic symmetry on wave velocities are investigated in the case of the aluminium alloy plate, which exhibits a texture due to rolling processes. Special calibration, performed on two test specimens, allows the effect of this texture to be taken into account. The acoustic birefringence technique is also used in the case of the aluminium plate to verify the stress distribution in the thickness. The results of surface residual stress distribution are compared with those obtained with an X-ray diffraction technique.

Crack deflection in ceramic/ceramic laminates with strong interfaces

Abstract: Crack deflection in electrophoretically deposited Al2O3/ TZ-3Y (3 mol% Y2O3-stabilized tetragonal ZrO2) lamellar composites with strong interfaces is described. The fracture behavior of, and crack paths in, these materials were evaluated using indentation and four-point bend tests. The effects of residual and induced stresses on crack deflection are considered.