Showing papers on "Residual stress published in 1977"

Mechanics of materials: An introduction to the mechanics of elastic and plastic deformation of solids and structural components

Abstract: Introduction Notation Unsymmetrical bending Struts Strains beyond the elastic limit Rings, discs and cylinders subjected to rotation and thermal gradients Torsion of non-circular and thin-walled sections Experimental stress analysis Circular plates and diaphragms Introduction to advanced elasticity theory Introduction to the Finite Element Method Contact stress, residual stress and stress concentrations Fatigue, creep and fracture Miscellaneous topics Appendices Index.

Fatigue Analysis of Cold-Worked and Interference Fit Fastener Holes

Abstract: Crack initiation and crack growth behavior were determined experimentally for aluminum and titanium specimens with fastener holes that were either cold worked or were propped by interference fit fasteners. The specimens were subjected to a randomized flight-by-flight spectrum. Analytical procedures were evaluated, based on correlation with the test data. These procedures included elastic-plastic analysis which was utilized to determine the stress-strain distributions surrounding the fastener holes. Estimates of elastic proportional limits in tension and compression were based on material cyclic stress-strain characteristics. Purely elastic analysis was used to determine the K T and stress gradient for the propped fastener holes with various ratios of plate-to-fastener modulus of elasticity. Finite-element model elastic-plastic computer results provided the stress-strain distributions for the cases of superimposed cold working and external loading, and superimposed interference fit fasteners and external loading. Approximate analytic equations were developed to fit the finite-element model computations. These equations were used to calculate the stress-strain excursions that would occur during flight-by-flight spectrum fatigue loading. The stress-strain excursions were then used to enter strain-life curves to compute crack initiation. They were also used to determine stress intensities to enter da / dn versus ΔK curves to compute crack growth. The delay in crack initiation due to beneficial compressive residual stresses that would be induced during spectrum loading was accounted for by using a stress ratio correction factor based on strain-life data generated at different stress ratios. Crack growth retardation due to periodically applied high loads was accounted for, using the Wheeler plastic zone model. The comparison of the crack initiation life calculations to the test data was favorable if initiation was defined as the development of a 0.25-mm crack. Good agreement between the crack growth calculations and the test data was also obtained for growth from a 0.25-mm crack.

Tests of fabricated tubular columns.

Abstract: Described herein are tests of 10 long fabricated tubular steel columns, of relatively large diameter, with essentially pine-ended conditions. In addition to the behavior, strength, and the manner of failure of the long columns, a number of stub column tests were also made along with the measurements of residual stresses. These residual stresses are both circumferential, due to formation of a flat plate into a cylindrical shape; and longitudinal, resulting from the welding of longitudinal seam needed to complete the fabricated cylinder. Measurement of these stresses is considered essential to any theoretical analysis of column behavior. The maximum strength of the 10 long columns tested (at diameter-to-thickness ratios of 48 and 70 and with a range of slenderness ratio between 39 to 83) is compared with the CRC column curve and good agreement is generally observed.

On the wrinkling of a free surface

Abstract: We consider an elastic half‐space whose free surface is capable of supporting its own stress field. This stress is a linear function of surface strain and is related to the stress in the interior of the body by a nonclassical boundary condition. We study the wrinkling (buckling) of the surface and show that this type of behavior is possible whenever the surface has a compressive residual stress or a negative stress‐strain modulus.

Fracture Behavior of ZrO2-Zr Composites

Abstract: Zirconium oxide-zirconium 2-phase alloys with composition 40 at.% Zr-60 at.% O (23 vol% metal phase) were prepared by hot-pressing mixtures of the oxide and the metal powders. The microstructure consisted of oxide grains completely surrounded by the metal phase. The effective fracture surface energy, γeff, was determined using the double cantilever beam (DCB) technique and crack lengths were determined by compliance calibration. Rapidly cooled specimens, in which the tetragonal to monoclinic phase transition would cause residual stresses, exhibited γeff values as much as 70% greater than stress-relieved specimens (65 J/m2 and 38 J/m2, respectively). A shift in the tetragonal ⇋ monoclinic transition temperature in the as-hot-pressed and the rapidly cooled specimens, compared to the stress-relieved specimens, confirmed the existence of residual stresses. The fracture strength, σeff, measured in 3-point bending, was found to be independent of the thermal treatments. Scanning electron microscopy and optical microscopy revealed that the fracture is transgranular.

Magnetic Studies of Residual Stress in Iron and Steel Induced by Uniaxial Deformation

Abstract: The nature of the residual stress in steel after uniaxial plastic deformation was investigated magnetically. The B-H curve measured in the residual stress state after elongation was similar to the one under compressive stress, and the induced magnetic anisotropy was uniaxial with the easy axis at right-angles to the previous direction of elongation. By employing a newly developed magnetic probe, which detects the sign and the magnitude of the induced uniaxial magnetic anisotropy under deformation, the magnetic yielding phenomenon was observed at the mechanical yield point. The probe output was highest at this point, compared with that observed during the subsequent cycles of loading. These results are interpreted semiquantitatively on the basis of the microscopic stress distribution and the anisotropy of the magnetostrictive strain.

Effects of residual stresses on the ductile strength of plane welded grillages and of ring stiffened cylinders

Abstract: Structural engineers have for a long time accepted the importance of residual stresses when considering fracture modes of failure. It is only in the last quarter-century that attention has been focused on their adverse effect on ductile modes of failure and, in particular, on buckling collapse. The last decade has seen increased research activity, spurred on by recent failures in box-girder bridges.The nature and distributions of locked-in-stresses during hot and cold forming and during welding are outlined. The effect these have on inelastic buckling collapse of flat plated grillages and ring-stiffened cylinders is examined for all likely modes of failure. Experimental data are scarce, but they confirm that both forming and welding stresses can reduce the stiffness and strength of both types of structure very significantly. This is caused by a direct reduction in buckling stresses (as usually supposed), but equally important is the loss in stiffness due to early yield and other effects. In partic...

Heat-treating method for pipes

Abstract: Disclosed is a method of heat-treating a pipe in which cooling water is passed through the pipe while the pipe is heated from the outer side thereof, so as to create a temperature differential between the outer and the inner sides of the pipe, so that the inner side of the pipe may be tension-yielded or the outer side of the pipe may be compression-yielded, thereby to generate a compressive residual stress and a tensile residual stress at the inner and the outer sides of the pipe, respectively.

Effect of laminate construction on residual stresses in graphite/polyimide composites: The effects of ply-stacking sequence and ply orientation on the magnitude of residual stresses were investigated experimentally in graphite/polyimide angle-ply laminates using embedded-strain-gage techniques

Abstract: The influence of ply-stacking sequence and ply orientation on the magnitude of lamination residual stresses in graphite/polyimide angle-ply laminates was investigated. The effect of stacking sequence was investigated with laminates of [02/±45]s, [±45/02]s, [0/+45/0/−45]s and [+45/02/−45]s layup. The effect of ply orientation was evaluated with additional specimens of [02/±15]s and [02/902]s layup. Thermal strains were measured using embedded-gage techniques. Residual strains were determined by comparing thermal strains in the angle-ply laminates with those of a unidirectional laminate. The ply-stacking sequence did not have an influence on the magnitude of residual strains. The highest residual strains occur in the [02/902]s laminate and the lowest, approximately one-fourth in magnitude, occur in the [02/±15]s laminate. The maximum residual strains in the [02/±45]s group are slightly lower than those in the [02/902]s laminate. Residual stress computations show that, at room temperature, the transverse-to-the-fibers stresses in all plies, except those of the [02/±15]s laminate, exceed the transverse tensile strength of the unidirectional material.

Prediction of Fatigue Crack Growth at Cold-Worked Fastener Holes

Abstract: A methodology for the quantitative prediction of crack-growth behavior of cracks emanating at cold-worked fastener holes under fatigue cyclic loading has been developed. The proposed prediction technique is based on an 4'effective stress field'1 concept that accounts for the amount of the compressive residual stress existing at the edge of the cold-worked hole. Stress-intensity factor ranges (A/0 and crack-growth rates (da/d/i) are all formulated in terms of the effective stress field. An existing fatigue-crack-growth analysis computer program has been modified to account for these changes. This program was subsequently used to study the fracturemechanics design development test data. Good correlations have been obtained.

The effect of matrix stresses on fibre pull-out forces

Abstract: A pull-out test was developed to measure the bond strengths and frictional forces between steel wires, and polycarbonate and epoxy matrices when the matrix was under tensile stress. Some debonding occurred due to the matrix stress. Despite this, the nominal bond strength, in the polycarbonate case, increased with increasing matrix applied stress. When the pull-out force had caused complete debonding, sliding under approximately constant friction coefficient,μ, occurred. The value ofμ for steel sliding in polycarbonate was 0.6, and for epoxy it was 0.19. The values were reduced to 0.12 and 0.10 respectively when the steel was coated with a fluorocarbon release agent. The normal stresses at the interface, in the absence of any applied stresses, were found to be about 7 MN m−2 in the polycarbonate, and 3.0 MN m−2 in the epoxy case. It was observed that the frictional forces due to these residual stresses could be less than one third of those generated by the applied stresses on the matrix. Thus residual stresses are not as important for fibre reinforcement as are matrix Poisson's shrinkage stresses.

Stress Corrosion Cracking of Zircaloy-2 Cladding in Iodine Vapor

Abstract: Iodine stress corrosion cracking of Zircaloy-2 cladding under static tensile stress has been studied over the temperature range of 250~450°C. The lowest iodine concentration required to cause cracking was 0.15 mg iodine per cm3 free volume in test ampoule at 300°C, and 1.1 mg/cm' at 350°C. The minimum circumferential plastic strain to cause failure was about 0.4% for specimen tubes possessing high cracking susceptibility. Softer tubes tolerate more circumferential deformation before they failed. This is attributed to greater margin retained for work hardening, rather than to smaller residual tensile hoop stress. Cracking was also inhibited by the presence of oxygen in the iodine atmosphere, the threshold partial pressures being 28 torr at 300°C and 9 torr at 350°C. Scanning electron micrographs of the fractured surfaces revealed brittle transgranular fracture carrying river patterns on part of the cleavage facets.

Analysis of Thermal Stresses and Residual Stress Changes in Railroad Wheels Caused by Severe Drag Braking

Abstract: A finite-element computer program, which takes into consideration nonlinear material behaviour after the yield point has been exceeded, has used to analyze the thermal stresses in railroad freight car wheels subjected to severe drag brake heating. The analysis has been used with typical wheel material properties and wheel configurations to determine the thermal stress field and the extent of regions in the wheel where the yield point is exceeded. The resulting changes in the residual stress field after the wheel has cooled to ambient temperature have also been calculated. It is shown that severe drag braking can lead to the development of residual circumferential tensile stresses in the rim and radial compressive stresses in the plate near both the hub and rim fillets.

Reflections on measurement of residual stress in rock

Abstract: Consideration of the behaviour of elastic bodies shows that it is not possible for a set of overcoring measurements that are made within isolated blocks to show residual strains or stresses that have a non-zero average, unless the size of the equilibrium volume over which the residual stresses balance is both considerably larger than the volume of the overcore and smaller than the size of the isolated block. Since some results have been reported that do not match these constraints, non-elastic behaviour must have occurred during overcoring. A possible explanation is that oriented microcracks are somehow opened by the overcoring. In some cases, stress fields induced by microcracking near the overcoring cut may explain measured strain changes far from the cut. Consideration of various reported measurements in terms of relative sizes of overcoring and equilibrium volumes shows that care is necessary when interpreting residual stress measurements.

Internal fatigue cracks are growing in vacuum

Abstract: Cylindrical specimens of 2024 and 7075 Al alloy material were heat treated with a cold water quench to obtain high residual tensile stresses at the interior. Fatigue tests showed internal cracks growing in the shear mode. By drilling a hole along the centre line internal cracks were given access to air, which then produced tensile mode cracks. Prestraining of specimens eliminated residual stresses thus producing crack initiation at the outer surface with crack growth in the tensile mode. Cracking in the tensile mode was sensitive to mean stress, whereas cracking in the shear mode was not. The shear mode crack on a micro level appeared to be slip band cracking.

Residual stress distribution in nitrided En41B steel as function of case depth

Abstract: Specimens of a ‘Nitralloy’ type of En 41B steel were subjected to glow-discharge nitriding at 525°C for between 0.5 and 24h in order to produce specimens with differing nitride case depths. Microhardness tests were used to determine the specimen case depth and to indicate the reproducibility between batches of nitrided specimens. The residual stress distribution was obtained by the Sachs boring technique. ‘Change-in-strain’ at the specimen surface was measured by four precision strain gauges connected in two separate Wheatstone bridge circuits. Strain functions were calculated from the strain data and a computer program was produced which fitted robust, weighted least-squares polynomials to these strain functions. The triaxial residual stress condition was obtained on differentiation of the fitted polynomials. The residual stresses introduced into the specimen by drilling were minimized to a consistent level for which corrections were made in the calculation of residual stress. Conditions of high ...

The role of thermal and residual stresses in linear elastic and post yield fracture mechanics

Abstract: The general role played by thermal and residual (TR) stresses in fracture mechanics is still unclear. It is sometimes argued (a) that in the linear elastic fracture mechanics (LEFM) regime TR stresses are secondary (rather than primary) i.e. that the overall loading is relaxed (rather than maintained) as well as redistributed as the crack grows, and (b) that because TR stresses do not influence the plastic limit load of a structure they have little influence on the post yield fracture mechanics (PYFM) regime. This paper demonstrates the dangers of these views. Examples are given of TR stresses behaving in either primary or secondary manner in both the LEFM and PYFM regimes. The danger of drawing general conclusions in fracture mechanics from the nearness of a structure to its plastic limit load is demonstrated, and it is shown that “local” rather than global (limit-analysis) collapse parameters must be used in empirical formulae that interpolate between LEFM and plastic-collapse regimes. In LEFM it is shown that the standard Green's function (weight or influence function) method can be applied to TR stress calculations. The method also applies in the PYFM regime if the Dugdale-type strip yield model is assumed. A general method of analysing fixed-grip loadings in the plastic regime, based on Rice's J contour integral is also given.

The indentation of hard metals: the role of residual stresses

Abstract: Experimental evidence to support Johnson's [6] analysis of the residual surface stress distribution produced in a flat surface by a spherical indenter is presented. The theory suggests that high residual stresses develop just outside the contact area as a result of the superposition of elastic unloading stresses onto the stresses at maximum load when the specimen has deformed plastically. The experiments involved the use of a semi-brittle steel, sufficiently hardened so that, while tensile stresses in the surface produced cracks, the substrate deformed plastically under the triaxial stress system beneath the indenter. Radial cracks produced by the indenter frequently extended after load removal, implying the presence of the high tensile circumferential residual stresses predicted by the theory. This work and recent studies of indentation loading of glasses show that there are important situations where residual stresses can contribute to their failure and wear.

Method and apparatus for reducing residual stresses in crystals

Abstract: A temperature profile controller is provided for cooling a crystal as it is pulled from a melt so that a substantially linear temperature gradient is established and maintained along the length of the crystal as it is cooled, whereby to prevent or reduce the occurrence of residual stresses in the crystal.

Apparatus and method for determination of residual stress in crystalline substances

Abstract: Apparatus and method for determination of residual stress in crystalline substances. An X-ray source is focused at two different, preselected angles with respect to a surface of a substance, and X-ray diffraction peaks are located with a single position-sensitive X-ray detector. The apparatus has positioning probes affixed to a base for maintaining the base in fixed relationship with the substance, and an arcuate glide channel formed in the base for controlled angular shifting of the X-ray source and detector. Residual stresses are determined more quickly than with prior art methods and apparatus having comparable precision because only a single detector is used, and because the detector locates diffraction peaks without time-consuming diffractometer shifting.

Measurement of residual stresses and distortions in stiffened panels

Abstract: Methods for measuring residual stresses and distortions in welded structures are described and initial results are given of a survey being carried out during manufacture of warship hull sections. The stresses are determined by measuring the elastic strain induced in the plate and stiffeners due to contraction of the stiffener welds, and profiles of the stiffener and plating after welding have been obtained. The survey is intended to provide information for use in future design calculations of the buckling strength of ship hulls.