Showing papers on "Residual stress published in 1970"

Stress and Volume Relaxation in Annealing Flat Glass

Abstract: Laboratory simulation of the industrial process of annealing sheet glass has yielded data on the genesis of stresses in initially stress-free glass. The experimental results differed from expectations based on classical annealing theory in that stresses began to develop in the annealing range even when the glass was being cooled at a constant rate, i.e. even in the absence of any changes of temperature gradients within the glass. Typically, these stresses account for 40% of the total residual stress in glass annealed according to a linear schedule. The remaining 60% are the well-known thermoelastic stresses that arise later in the annealing process from the decay of temperature gradients in the glass. The stresses observed to arise in glass as it is being cooled at a constant rate are attributed to volume relaxation effects which, in parts of the annealing range, generate stresses rapidly enough that they are not dissipated by stress relaxation. A mathematical model of annealing is proposed that takes account of both stress and structural relaxation. The model fits the experimentally observed evolution of stresses during linear cooling. It also suggests that (with the activation energies of stress and structural relaxation about the same) the actual rate, at any given temperature, of structural relaxation is about 4 times lower than that of stress relaxation.

with residual stresses

Abstract: For a growing crack the residual stresses caused by plastic flow at previous positions of the crack-tip affect the current plastic zone. This effect is calculated by an extension of the BCS model which replaces the plastic zone by two planar arrays of dislocations emanating from the crack-tips. For a growing crack a succession of such axrays is formed. We consider a crack growing in anti-plane strain with the slip-planes making an almost zero angle with the plane of the crack. The plastic zone size in front of the crack turns out to be the same as for a stationary crack, while the relative displacement of the crack faces is less concentrated in the vicinity of the crack-tip. The rate of plastic dissipation of energy is calculated, and turns out to be identical with the elastic energy release rate. The earliest solution for the elastic-plastic field near the tip of a crack was obtained by Hult & McClintock (I 956). These authors considered a crack in an infinite medium deformed in anti-plane strain (mode III) and -showed that for perfectly plastic material the plastic zone at low stresses was a circle with circumference passing through the crack-tip. This analysis holds for a crack of fixed length, whereas many situations involve growing cracks, for which the residual stresses in regions which suffered plastic deformation at earlier positions of the crack-tip will affect the nature of the current plastic zone. Thus, for example, the criteria for the initial instability of monotonically loaded crack and for the continued growth of an already growing crack will in general not be identical. The need for consideration of the growing crack problem has led Chitaley & McClintock (I968) to look at the case of steady growth im mode III under constant stress intensity factor. They show that the length of the zone in the forward direction is almost the same as for the static case, but the whole forward zone is included within an angle of roughly 400 from the crack-tip. Furthermore, there are small zones of reversed plastic flow along the flanks of the crack, although their thickness is only 1/40 of the thickness of the forward zone, and neglecting to include them makes an insignificant difference in the resulting properties of the forward zone. The plastic displacement at the crack-tip is reduced to 7 % of its value for an identically loaded stationary crack. An alternative approach to calculating crack-tip plasticity has been given by Bilby, Cottrell & Swinden (i963) (referred to as B.C.S.) who represent the plastic zone by a continuous array of dislocations, coplanar with the crack. In terms of the

Enhanced oxidation of molybdenum disilicide under tensile stress: relation to pest mechanisms.

Abstract: The mechanical disintegration of molybdenum disilicide in air or oxygen at temperatures of 300° to 600°C, known in the literature as “pest”, is ascribed here to stress enhanced oxidation at the tips of Griffith flaws, eventually leading to brittle fracture. Stress-free single crystals of molybdenum disilicide, which are not ordinarily subject to pest, were shown to exhibit delayed failure in four-point bend tests under the conditions that lead to pest in polycrystals. The delayed failure times showed the same temperature and oxygen pressure dependence as the times to onset of pest disintegration in polycrystals. Pest in polycrystals occurs even in the absence of an applied stress, due to the high residual stresses which are introduced upon cooling this highly anisotropic material from the melt during fabrication. Nonetheless, the superposition of an applied stress, over and above the residual stress, was shown to decrease the time to pest failure compared to unstressed specimens. The absence of pest above 600°C, and the longer times required for pest disintegration as temperature is increased above about 500°C, is explained by the presence of plastic deformation in the matrix, which tends to reduce stress concentration at the tips of flaws and to counteract the flaw sharpening effect of stress enhanced oxidation. Slip was readily observed at 600°C. The delayed failure results were consistent with the general Charles-Hillig model for the mechanical failure of brittle materials that react chemically with their environment.

An investigation of the hole-drilling technique for measuring planar residual stress in rectangularly orthotropic materials

Abstract: The applicability of the semidestructive holedrilling technique to the experimental determination of residual stresses in relatively thin rectangularly orthotropic materials was investigated. From the exploratory work, it was determined that the similitudes, for measurements at a particular ratio of hole depth to diameter, which exist for thick materials are not present in relatively thin materials. This implies that calibration tests must be made for each combination of strain-gage size and plate thickness. As a consolation, however, it was found that there is no need to drill to an optimum depth for thin materials. That is, one may simply drill a small hole completely through the material to obtain the desired strain change.

Stress and deflection analysis of mechanically fastened joints

Abstract: : The report presents analytical techniques for predicting both the linear and nonlinear stresses and deformations of mechanically fastened joints. The idealization used is a set of stacked parallel plates which transfer planar loads among themselves by means of transverse fasteners. The plates are treated by finite element methods of matrix structural analysis in which each element is assumed to be in plane stress for both elastic and plastic stress states. The fasteners, which are treated by short-beam theory, interact with the plates under the assumption that the plates may be represented by an equivalent elastic foundation. Application of the present analytical techniques was made to a variety of problems including: the combined elastic-plastic behavior of plates with unloaded holes, the load-deflection behavior of single-fastener joints, the residual stress distributions in plates with squeeze rivets, the effect of fastener bending and shear deformation on the bearing stress distribution between the fastener and the plate, and the prediction of the fatigue life of typical mechanically fastened joints. In all these cases, comparisons with test results generally gave very good correlation. For the range of parameters studied, the effects of hole clearance and fastener interference and geometric configuration appear to play the dominant roles in determining the stress distribution and hence, the fatigue life of mechanically fastened joints.

Solid Cadmium Embrittlement: Titanium Alloys

Abstract: The phenomenon, solid cadmium embrittlement, was identified and studied in the titanium alloys Ti-6Al-4V and Ti-8Al-1 Mo-1V using cadmium coated tensile specimens and residual stress speci...

Deformation behavior of continuous-fiber metal-matrix composite materials

Abstract: The deformation behavior of continuous-fiber, metal-matrix composites was studied in terms ofin situ deformation behavior of the matrix and the fibers. X-ray diffraction techniques were employed to monitor the stress-strain behavior of the composite components (matrix and fibers) as a function of total composite stress-strain behavior. This experimental technique provided a unique approach to the study of metal-matrix composites since the deformation response of the components could be measuredin situ while the composite was under load. Furthermore, the influence of residual stress, component mechanical properties, and stress interactions between the matrix and the fibers could be incorporated into the analysis of composite deformation behavior. The study was conducted on composites of 2024 aluminum reinforced with tungsten fibers, and composites of 2024 aluminum reinforced with boron fibers. Composites were tested on a specially-designed, tensile device which served as a diffractometer specimen holder such that diffraction experiments could be performed while the specimen was incrementally deformed in uniaxial tension. Experimental results indicated that, except for the residual stress effects, the composites exhibited rule-of-mixture s behavior in the stage I, II, and in deformation regions. Measurements obtained perpendicular to the fiber and tensile axis during the tensile tests indicated that negligible stresses were developed as a result of Poisson’s ratio differences between the matrix and the fibers. Composite yield behavior was significantly influenced by residual stresses present in the individual components. Residual stresses parallel to the fiber axis could be included in the rule-of-mixtures analysis by considering the amount of prestrain which was present in each component.

Theoretical stresses and strains from heat curving

Abstract: HORIZONTALLY CURVED STEEL GIRDERS FOR CURVED HIGHWAY BRIDGES CAN BE ECONOMICALLY FABRICATED BY BUILDING A STRAIGHT GIRDER AND THEN HEATING APPROPRIATE FLANGE EDGES TO INDUCE A RESIDUAL CURVATURE AFTER COOLING. THE RESULTS OF A THEORETICAL INVESTIGATION OF THE RESIDUAL STRESS, STRAIN, AND CURVATURE DUE TO THIS HEAT-CURVING PROCESS PROCESSES ARE PRESENTED. THE ANALYTICAL MODEL USED A PERFECT ELASTIC-PLASTIC, TEMPERATURE-DEPENDENT STRESS-STRAIN RELATIONSHIP FOR THE STEEL, AND TEMPERATURE PROFILES IN THE GIRDER FLANGES BASED ON HEAT-TRANSFER THEORY FOR A SEMI-INFINITE PLATE. THE EFFECTS OF MAXIMUM EDGE TEMPERATURES TO 1,150 DEGREES F OVER INCREASING WIDTHS OF THE FLANGES OF A TYPICAL GIRDER WERE DETERMINED. THE RESIDUAL STRESSES AFTER HEAT CURVING WERE TENSILE NEAR THE FLANGE EDGE AND COMPRESSIVE ELSEWHERE, EXCEPT NEAR THE CENTER OF THE FLANGE, WHERE TENSILE STRESS SOMETIMES REMAINED. THE FINAL CURVATURE, WHICH WAS DETERMINED FROM THE RESIDUAL STRAIN DISTRIBUTION, GENERALLY INCREASED WITH MAXIMUM TEMPERATURE. /ASCE/

Machining of High Strength Steels with Emphasis on Surface Integrity.

Abstract: : As the strength level of High strength steels increases, fatigue and stress corrosion resistance exhibit a marked increase in sensitivity to surface conditions produced in machining. There are several significant surface alterations produced in machining which can seriously affect fatigue and stress corrosion resistance. These include untempered martensite, overtempered martensite, plastic deformation, cracks, tears, laps, burrs, spattered or redeposited metal, and residual stress. The effect of machining conditions on the formation or avoidance of these surface alterations is discussed in detail. Machining relationships and recommendations are given for chip removal operations, abrasive operations, as well as nonconventional operations, to minimize surface alterations. To maintain high surface integrity in milling, turning, drilling, etc. machining conditions are selected to provide long tool life. In addition, tools must be kept sharp, that is, tools must be changed frequently to minimize metallurgical alterations within the surface layer. In grinding, low wheel speeds, light down feeds, together with the use of highly active cutting oils are necessary to minimize surface alterations. Post-operative machining processes, such as heat treatment and shot peening are often needed to obtain desirable surface conditions. Rigid inspection techniques and often repair procedures are required to insure proper surface integrity. Particular attention is given to the problem of drilling and reaming holes with high surface integrity in high strength steels. (Author)

Structural Investigation of Thin Films

Abstract: In the investigation of the structural properties of thin films by x-ray diffraction the lack of material, interference from the substrate, and generally, high orientations of the grains makes analysis of the films very difficult In order to fully characterize a thin film for stresses (macro- and micro-), grain size, orientation, faulting probability, and solid solution effects, it is necessary to employ a range of x-ray techniques with some special experimental conditions It is shown that a full strnctural analysis of thin films (alloy films included) can be routinely carried out making comparison of different types of thin film possible Two 12-kA-thick Al films are characterized and it is shown that large errors can occur in residual stress and solid solution effect if the data is not handled properly

Residual Stresses Induced By Hole Cold Expansion

Abstract: This paper describes an X-ray diffraction technique for measuring residual stresses. The results of measurements at locations in the vicinity of plain and cold expanded holes in an aluminium alloy are presented. Residual stresses are shown to vary significantly in all three dimensions and two dimensional analyses commonly used for residual stress determination are shown to be inadequate. The results of a fatigue test programme are also presented in which simple aluminium alloy specimens containing plain and cold expanded holes were subjected to constant amplitude fatigue loading. The results show that cracks from plain holes continuously increase in growth rate to failure whilst cracks from cold expanded holes decrease in growth rate and frequently arrest. The arrested crack lengths are different on either face of the cold expanded specimens and this is equated to the different residual stress fields present. Fatigue crack growth rates predicted using a Green's function technique are compared with those measured experimentally.

Effect of Residual Stresses on the Low Cycle Fatigue Life of Large Scale Weldments in High Strength Steel

Abstract: Effect of residual stresses on the low cycle fatigue life of large scale weldments in high strength steel

Thermal Expansion of Composites as Affected by the Matrix

Abstract: Summary and Conclusions Thermal expansion measurements of composite systems containing hard dispersions embedded in brittle and semibrittle matrices indicate the importance of (1) the magnitude of the stress developed in the matrix and (2) the crack propagation behavior of the matrix. The thermal expansion of these composites can be predicted if the residual stress developed as a result of the difference in the expansions of the components does not exceed a critical value defined by the modified Griffith equation. This critical stress varied considerably with the nature (brittle, semibrittle, or ductile) of the matrix.

Methods for magnetically measuring stress using the linear relationship of the third harmonic to stress

Abstract: A method for determining applied stress, yield stress and residual stress in a magnetic material. The method utilizes the amplitude of an induced third harmonic signal as an indication of the stress. Two measurements of the third harmonic amplitude are made, one for an unstressed and a second for a stressed condition. The amplitude indicative of the stress in the material is compared to the initial third harmonic reading according to a linear relationship to determine the stress.

3-d Axisymmetric Numerical Analysis And Experimental Study Of The Fastener Hole Coldworking Process

Abstract: Most theories developed for the determination of the residual stresses and strains near the edge of a coldworked hole have been based on two-dimensional analysis considerations. They do not reflect faithfully the actual situation because of the three-dimensional nature of the coldworking procedure. In the present work, the ABAQUS finite element computer program was used to simulate the three dimensional behaviour of a cold expanded fastener hole. The through thickness hole profile and the variation in residual stresses and strains on both lateral surfaces and in the centre of the plate are studied and compared with experimental measurements of the residual stresses on both surfaces together with the values obtained from theoretical models proposed in the literature. Since the present analysis takes into account the non-uniformity of the coldworking procedure through the thickness of the hole, the proposed model may effectively be used to study the effect of the coldworking parameters on the residual stress distribution and thereby on fatigue life.

Fracture Induced in Al2O3 Bicrystals by Anisotropic Thermal Expansion

Abstract: Bicrystals of Al2O3 were fabricated to study the effects of thermal expansion anisotropy on fracture in a model system containing one grain boundary. Fractures occurred perpendicular to the directions of maximum tensile stress in bicrystals with thermal expansion coefficient differences as low as 0.31×10−60C−1 and originated at the boundary, probably in areas of high residual stress associated with pores. Numerical stress analysis of two-dimensional model bicrystal configurations showed that stresses induced by thermal expansion anisotropy are maximal in a region localized along the bicrystal boundary.

Experimental Stresses and Strains from Heat Curving

Abstract: To obtain information on the heat curving process for the fabrication of horizontally curved highway bridges, an analytical and experimental investigation was conducted to determine the residual stresses, strains, and curvature in a typical heat-curved girder. The analytical results were reported separately. The 52-ft-long test girder was a typical welded, A36 steel, plate girder. Residual stresses before heat curving were determined by sectioning. The remaining 46-ft-long girder was curved to a radius of 397 ft in six successive runs by using a continuous heat-curving process. Strains and temperatures were recorded during each run, and the residual stress, strain, and curvature after each run were determined. The behavior of the girder was in agreement with the analytical investigation. When compared with the experimental values, the analytical solution satisfactorily predicted the residual stresses but under-estimated the residual curvature.

Solid Solution Effects in Thin Aluminum Films

Abstract: The effect of a solid solution of hydrogen, oxygen, nitrogen, or water vapor in the lattice of thin films of Al was studied by x-ray diffraction. The lattice parameter shift due to solid solution effect independent of residual strain or faulting was observed. This method is applied to thin films to determine nondestructively whether there are low concentrations of impurities affecting the lattice of the films. It is also shown that large errors occur in the value of the residual stress measured by certain x-ray techniques or in that of the solid solution concentration if both of these effects are not taken into consideration during the subsequent calculations.

Hot-salt stress-corrosion of a titanium alloy in a dynamic air environment

Abstract: Hot-salt stress-corrosion threshold data were determined for the Ti−8Al−1Mo−1V alloy under simulated turbine-engine compressor environmental conditions Threshold data determined by residual tensile ductility were demonstrated to be a more sensitive indication of hot-salt stress-corrosion than threshold data determined from crack observations Specimens that had been stress-relieved by chemically milling exhibited drastically lower threshold stresses than did specimens in the as-machined condition A Mach 07 airflow with a dewpoint of−120° F did not significantly reduce stress-corrosion when compared to static air conditions

Theoretical aspects of residual stress measurements by x‐ray diffractometry

Abstract: This paper is the first in a series of three covering (1) theoretical considerations, (2) experimental features, and (J) practical applications of X-ray diffractometer techniques to the accurate determination of residual macrostresses.

Microstructure And Residual Stress Analysis Of A 'rimChilled' Solid Wheel For Rail Transportation System

Abstract: The "Rim Chilling" treatment on a railway wheel has been simulated by means of heat transfer and thermal stress fern analyses. Both the microstructure and the residual stress distribution after the chilling have been numerically predicted and verified by means of micrographic observations and strain gauge measurements. A good agreement was found between numerical and experimental results.

Crack Initiation at Stress Concentrations as Influenced by Prior Local Plasticity

Abstract: Notched metal crack initiation, determining high cyclic loads effects by prior local plastic behavior at stress concentration

Stress Analysis of Multilayer Pressure Vessel

Abstract: Multilayer pressure vessel is designed to work under high pressure condition. In this paper, the stress analysis of multi-layer pressure vessel made of a homogeneous and isotropic material and subjected to internal pressure is considered. The hoop stresses for 1, 2 and 3-layer pressure vessel is calculated theoretically. The modeling of pressure vessel is carried out in CATIA V5 and this model is imported in ANSYS Workbench where stress analysis is carried out. The shrink fit is applied during the CAD modeling of multilayer pressure vessel. Both theoretical and FE results are compared and effect of multi-layering on stresses induced and the volume requirement to sustain the given pressure is calculated. Also optimization of number of layers is carried out for multi-layering the pressure vessel. From calculations it is observed that as the numbers of layers increases, the hoop stresses decreases

Technique for the Direct Observation of Residual Defect Structures in Explosive Loaded Metal Cylinders

Abstract: A new technique has been devised to examine deformation microstructures of thin walled metal cylinders subjected to internal impulsive loading The cylinders are strained finite amounts but are not carried to fracture The stressing device uses a rigid stainless steel cell as a container and an explosively driven Lucite core to produce specimens of metals and alloys that have undergone a high strain rate expansion and are in a form amenable to direct observation by transmission electron microscopy The total strain in the specimen is controlled and loading conditions may be reproduced for comparison of different materials This approach is particularly well suited to the detailed investigation of explosive forming processes and shock hardening phenomena in cylindrical bodies