Showing papers on "Residual stress published in 1997"

Structural and residual stress analysis by nondestructive methods : evaluation, application, assessment

Abstract: X-ray diffraction, V. Hauk et al neutron diffraction methods, L. Pintschovius ultrasonic techniques, E. Schneider micromagnetic techniques, W.A. Theiner assessment of residual stresses, B. Scholtes.

Residual stress improvement in metal surface by underwater laser irradiation

Abstract: Laser shock processing of water-immersed material was developed for improving the residual surface stress of metal components. The process changes the stress field from tensile to compressive by means of impulsive pressure of laser-induced plasma generated through the ablative interaction of the intense laser pulse with the material. The plasma, generated by the irradiation of second harmonic of a Q-switched Nd:YAG laser (SH-YAG, λ = 532 nm) on an SUS304 test piece, was directly observed by imaging the plasma radiation with a gated image intensifier and a charged coupled device (CCD) camera. Comparing the observed image to the plasma expansion velocity calculated with an analytical model, we deduced that about 20% of the plasma internal energy would represent the thermal energy. The calculation of the plasma pressure with this result showed that it exceeded 2 GPa in water and the yield stress of SUS304, when a typical laser pulse of the SH-YAG impinged on a water-immersed SUS304 test piece. A residual compressive stress exceeding 200 MPa was built over 200 μm in depth, by scanning the SH-YAG focused on a spot of 0.75 mm diameter with a power density of 60 TW/m2 and a pulse duration of 5 ns.

Material Properties Models for Analysis of Cold-Formed Steel Members

Abstract: The development and accuracy of an appropriate analytical model to predict the behavior of cold-formed steel (CFS) structural members necessitate a correct representation of the corresponding material characteristics. The results of two series of experimental investigations to evaluate the mechanical properties and the built-in residual stresses of CFS sections are reported in this paper. These investigations were performed on channel-shaped CFS sections manufactured using the cold-roll forming technique. Tensile coupon tests were used to evaluate the mechanical properties at different locations such as flat area, and the corner areas, of the channel sections. Electrical resistance strain gauges with an “electrical discharge machining” cutting technique were used to establish the magnitudes and the distributions of residual stresses within the channel sections. Based on the experimental results, appropriate analysis models for the stress-strain relationship, the variation of the yield strength, and the re...

A micro strain gauge with mechanical amplifier

Abstract: A passive micro strain gauge with a mechanical amplifier has been designed, analyzed, and tested. The mechanical amplifier provides a high gain such that residual strain in thin films can be directly measured under an optical microscope. This strain gauge can be in situ fabricated with active micro sensors or actuators for monitoring residual strain effects, and both tensile and compressive residual strains can be measured via the strain gauge. It is shown that a very fine resolution of 0.001% strain readouts can be achieved for a micro strain gauge with a 500 /spl mu/m-long indicator beam. Beam theories have been used to analyze the strain gauge with a mechanical amplifier, and the results were verified by a finite-element analysis. Experimental measurements of both polysilicon and silicon-riched silicon-nitride thin films fabricated by surface micromachining processes are presented.

LAYERED CERAMICS: Processing and Mechanical Behavior

Abstract: ▪ Abstract Recent progress in the field of mechanical behavior of layered ceramics is reviewed. Several processing techniques are described with reference to the fabrication of ceramic laminates. These include tape-casting, centrifugal casting, slip-casting, electrophoretic deposition (EPD), and the production of fibrous monolith materials. The review discusses various laminar design approaches for achieving improvements in strength, toughness, work of fracture, R-Curve behavior, and contact damage resistance. Examples of effective strategies include manipulation of residual stresses, the incorporation of weak interlayers to induce crack deflection, and promotion of synergistic effects between layer materials that exhibit intrinsically different responses.

Polycrystalline diamond cutter with integral carbide/diamond transition layer

Abstract: A composite body cutting instrument formed of a polycrystalline diamond layer sintered to a carbide substrate with a carbide/diamond transition layer. The transition layer is made by creating carbide projections perpendicular to the plane of the carbide substrate face in a random or nonlinear orientation. The transition layer manipulates residual stress caused by both thermal expansion and compressibility differences between the two materials and thus increases attachment strength between the diamond and carbide substrate by adjusting the pattern, density, height and width of the projections.

Attachment geometry for non-planar drill inserts

Abstract: A manufacturing method and a drill bit composite insert for performing mechanical actions that require high wear and impact resistance are provided. The composite insert has improved interface strength and improved residual stress distribution. These improved features are achieved by chemically and mechanically attaching the layer of abrasion and corrosion resistant polycrystalline material to the substrate that ordinarily is tungsten carbide. The chemical bond is formed during high pressure and high temperature sintering. Mechanically, the abrasion and corrosion resistant layer is attached to the substrate by means of irregularities on the substrate's top surface. These irregularities are designed to distribute stress and minimize the number of features that would lead to crack formation and subsequent failure of the insert. These surface irregularities are not sculptured features on the substrate that are of difficult or impossible manufacture, but they can be manufactured by pre- or post-sintering shaping methods.

An Axisymmetric Method of Elastic-Plastic Analysis Capable of Predicting Residual Stress Field

Abstract: Linear elastic solution of an axisymmetric boundary value problem is used as a basis to generate its inelastic solution. This method treats the material parameters as field variables. Their distribution is obtained as a part of solution in an iterative manner. Two schemes of updating material parameters are discussed and compared. A procedure for calculation of residual stress field is presented. Application of the method to autofrettage is presented. Residual stress calculation based on actual material curve, isotropic and kinematic hardening models, and variable Bauschinger effect factor (BEF) is carried out. It is concluded that consideration of dependency of BEF on plastic strain makes significant changes to residual hoop stress near the bore for low-level autofrettage. However, this dependency is insignificant for high-level autofrettage. Results obtained here are shown to be in good agreement with experimental and finite element results.

Strain and hysteresis by stochastic matrix cracking in ceramic matrix composites

Abstract: A theory is presented to predict the stress/strain relations and unload/reload hysteresis behavior during the evolution of multiple matrix cracking in unidirectional fiber reinforced ceramic matrix composites (CMCs). The theory is based on the similarity between multiple matrix cracking and fiber fragmentation in a single fiber composite, and determines the crack and strain evolution as a function of the statistical distribution of initial flaws in the material, the interfacial sliding resistance tau, and the thermal residual stresses in the composite. The model properly includes matrix fragments of all lengths, from lengths smaller than the current slip length delta(sigma) to larger than 2 delta(sigma), at applied stress sigma, and accounts for their respective and differing contributions to the overall strain and hysteresis behavior of the composite. The procedure by which experimental stress/strain and hysteresis data can be interpreted to derive values for the interfacial shear stress, thermal stresses, and intrinsic matrix flaw distribution is discussed. The actual physical crack spacing needs only to be determined at one load level, such as post-fracture, which greatly simplifies the data acquisition and analysis. Several detailed examples are presented, and the results compared with a widely-used approach in which the crack spacing is assumed constant and equal to the average spacing obtained directly from experiment. The discrepancy between the previous and present theories is manifest in an incorrect estimate for the interfacial sliding, but only by approximately 10%. The effect of changing temperature, and hence residual stresses, without changing either matrix flaws or interfacial sliding resistance, is studied. (C) 1997 Elsevier Science Ltd.

Fracture Mechanics of Composites With Residual Thermal Stresses

Abstract: The problem of calculating the energy release rate for crack growth in an arbitrary composite in the presence of residual stresses is considered. First, a general expression is given for arbitrary, mixed traction, and displacement boundary conditions. This general result is then applied to a series of specific problems including statistically homogeneous composites under traction or displacement boundary conditions, delamination of double cantilever beam specimens, and microcracking in the transverse plies of laminates. In many examples, the energy release rate in the presence of residual stresses can be reduced to finding the effect of damage on the effective mechanical properties of the composite. Because these effective properties can be evaluated by isothermal stress analysis, the effect of residual stresses on the energy release rate can be evaluated without recourse to any thermal elasticity stress analyses.

Prediction of welding deformation and residual stress by elastic FEM based on inherent strain. Report 1: Mechanism of inherent strain production

Abstract: Prediction of Welding Deformation and Residual Stress by Elastic FEM Based on Inherent Strain (Report I) : Mechanism of Inherent Strain Production(Mechanics, Strength & Structure Design) Author(s) Luo, Yu; Murakawa, Hidekazu; Ueda, Yukio Citation Transactions of JWRI. 26(2) P.49-P.57 Issue Date 1997-12 Text Version publisher URL http://hdl.handle.net/11094/7958 DOI rights 本文データはCiNiiから複製したものである Note

On the initial unloading slope in indentation of elastic-plastic solids by an indenter with an axisymmetric smooth profile

Abstract: A simple relationship between the initial unloading slope, the contact area, and the elastic modulus is derived for indentation in elastic-plastic solids by an indenter with an arbitrary axisymmetric smooth profile Although the same expression was known to hold for elastic solids, the new derivation shows that it is also true for elastic-plastic solids with or without work hardening and residual stress These results should provide a sound basis for the use of the relationship for mechanical property determination using indentation techniques

Modelled and measured residual stresses in plasma sprayed thermal barrier coatings

Abstract: Thermal barrier coatings consisting of a NiCrAlY bond coating and a 1.4 mm thick partially stabilised zirconia top coating were air plasma sprayed onto grit blasted nickel-base substrates. Two samples were produced using different amounts of external cooling during spraying of the top coatings. The residual stress profiles in the samples were measured after each manufacturing process step with a layer removal technique. A finite element model including a thermal analysis and a stress-strain analysis of the deposition was developed to model the origin of the thermal stresses and to verify the measured residual stresses. The main components for the residual stresses in the sprayed coatings were identified as stresses developing during the rapid cooling of individual droplets (quenching stresses) and stresses formed during cooling from deposition temperature to room temperature. The quenching stresses were predicted to be low and tensile in the top coating, due to stress relaxation by formation of vertical microcracks. During cooling to room temperature, compressive stresses were superimposed on the top coating quenching stresses. The final residual stresses were predicted to be compressive in the top coating. This was confirmed by measurements (−15 MPa). In the bond coating, no stress relaxation by microcracking was observed and the residual stresses were found to be tensile (~100 MPa). In the substrate, compressive residual stresses reaching −200 MPa were found in a zone to a depth of 0.3, mm into the substrate. The stresses were found to have originated during the grit blasting of the substrates prior to bond coating deposition. A correlation between modelled inelastic strain and measured densities of vertical microcracks in the top coating was obtained. High values were found close to the bond coating, which were correlated to a low substrate temperature during spraying of the top coating material.

The influence of a heat treatment on the microstructure and mechanical properties of sputtered coatings

Abstract: The aim of this paper was to examine correlations between deposition parameters and the coating properties of RF-sputtered films in deposition conditions and after heat treatment at temperatures up to 700 °C. The investigations deal with titanium-, chromium- and hafnium-based nitrides, borides and ternary alloys. Different materials such as SAE 52100 steel, ASP 23 high-speed steel and Ti6A14V titanium alloy, which are commonly used in the aerospace industry, were coated to analyse the influence of the substrate material. The coatings were tested with respect to their phase composition, microstructure, residual stress, thickness, microhardness and adhesion. It is shown that the deposition parameters, as well as heat treatment at a temperature as low as 400 °C, can change considerably the coating properties.

Residual stresses and crystallographic texture in hard-chromium electroplated coatings

Abstract: The X-ray diffraction method was used to study the structural and mechanical state of etectrodeposited chromium coatings Experiments were performed on layers of various thicknesses, plated on different types of substrates, and the evolution of the stress state as a function of depth was studied The dependence of the texture on the thickness of the coatings and the substrate material was also studied The effects of the texture on the values of the X-ray elastic constants (XEC) were taken into account using the orientation distribution function (ODF) or the crystallites group method The elastic behaviour of the diffracting domains was studied in 3 ways: using the anisotropic self-consistent Kroner-Eshelby model, assuming Reuss' hypothesis, and considering the isotropic case Final values of residual stresses are compared and a simple method of evaluation is proposed The chromium deposits were plated by direct current They are very cracked and exhibit a fibre texture with a 〈111〉 axis The residual stresses are tensile with values about 800 MPa at the surface, decreasing with depth according to the thickness of the layer, and increasing again at the coating-substrate interface

PVD CrxN coatings for tribological application on piston rings

Abstract: Besides the established PVD coatings for the wear protection of machining tools, this paper deals with coating development and model wear test results from PVD coatings on piston rings for combustion engines. Piston rings are examples for the application of thin films on commonly used mechanical components. The PVD Cr x N coatings are deposited by RF magnetron sputtering and characterized by their fundamental mechanical properties like thickness, hardness, residual stress and adhesion, which are important for the tribological behaviour of the coating substrate compound. The contact mechanics of the tribological system piston-ring–cylinder are determined by high mechanical loading and changing geometry caused by the sliding kinematics. Therefore, the range of thickness is about 7 μm. The selected rings are made of steel DIN 1.4112 (DIN X 90 Cr Mo V 18) with a bore diameter of 97.5 mm. The results of the coating substrate characterization — high hardness, moderate compressive residual stresses and sufficient adhesion on metallic substrates — provide good behaviour of coatings in this tribological application. This is confirmed by the results of the tribological test procedures which have been performed with ring-on-disc model-wear tests and a short-stroke test rig.

Can steel fibers replace transverse reinforcements in reinforced concrete beams

Abstract: Steel fiber reinforced concretes currently used do not have enough post-cracking tensile strength to be used alone, without main reinforcement (rebars), in a beam. On the other hand, replacement of the secondary reinforcement (stirrups) seems promising. The use of fibers would save considerable time and would facilitate placement in highly reinforced structures. A large experimental program was carried out to quantify the mechanical contribution of fibers in beams. In a first step, five large scale double-T-girders were tested, with the transverse reinforcement varied - concrete only, stirrups, or fibers. A global optical method, stereophotogrammetry, was used to monitor cracking. It showed a mainly mode I crack opening process. Furthermore, these tests suggested a scale effect linked to the height of the beam: the higher the height of the beam, the wider the crack opening at failure, i.e. the smaller the residual stress carried by the fibers. These findings lead to optimize both material and structure in regard to shear behavior. A high-strength steel fiber reinforced concrete was used in small rectangular beams, 0.25-m high, to provide high residual stress of the material and small crack opening at failure. For both types of beams--T-girders and rectangular beams--the mix was optimized using the Baron-Lesage method and the mechanical characterization of the material was conducted using a uniaxial tensile test monitored by the rate of the crack opening. A method of analysis based on a block mechanism is proposed and compares well with experiments.

Experimental determination of stress intensity factors due to residual stresses

Abstract: An experimental method is presented that enables stress intensity factors due to residual stress to be determined directly, without prior determination of the residual stress. The method is based on the crack compliance method, where a narrow cut is introduced progressively into the considered component, and the resulting strain change is measured by a strain gage. The required mathematical relations to determine stress intensity factors from strain measurements are established by means of some basic relations of linear elastic fracture mechanics. They are derived explicitly for two exemplary geometrical systems, which allowed for analytical treatment. Experimental data obtained in the case of a steel roller are presented and discussed.

Viscoelastic analysis of processing-induced residual stresses in thick composite laminates

Abstract: Residual stresses induced during the processing of thick composite laminates are analyzed. A two-dimensional thermochemical analysis is used to obtain temperature and degree of cure distributions during cure. A two-dimensional finite-element model is developed to predict the residual stress history in rectangular laminated plates. A cure-dependent visco-elastic material model is used in the analysis. Both unidirectional and cross-ply laminates are investigated. Unidirectional laminates are studied because residual stresses in this class of laminates is driven purely by thickness effects. Regardless of the layup,for moderately thick (2.54-cm) laminates the nonuniformities in temperature and degree of cure are mild. As a result, the development of residual stress is very similar to the analysis of thin laminates. For laminates of large thickness (7.5 cm), stronger variations in temperature and degree of cure develop during the cure cycle. The development of residual stress in this case is more complex. The ...

A finite element simulation of the cold working process for fastener holes

Abstract: Two-dimensional axisymmetric finite element simulations have been conducted for the cold working of a fastener hole in an aluminium plate. The simulation models the actual cold working process where an oversize mandrel is pulled through the fastener hole. The results of the simulation are compared with a simplified finite element model where the cold working process is reduced to applying a uniform radial expansion to the hole edge. It is shown that substantial differences exist between the finite element simulations; specifically, the simulation of the actual process shows tensile residual radial stresses on the surface of the plate after cold working whereas the simplified simulation shows only compressive ones. Further comparisons are made for the axial deformation of the plate by using the results of an experimental measurement of the surface profile around a cold worked hole. There is good agreement between the finite element and experimental results. The results of this work show that accurate simulations of cold working are necessary if predicted residual stresses are to be used to assess fatigue life.