Showing papers on "Residual stress published in 1971"

Plastic Deformation of Aluminum Oxide by Indentation and Abrasion

Abstract: Transmission electron microscopy provided direct evidence that plastic deformation occurs during the room-temperature indentation and abrasion of Al2O3. Examination of single-crystal and polycrystalline specimens showed that high densities of dislocations are produced within the near-surface regions by mechanical polishing with a fine diamond compound (0.25 μm) and that plastic deformation by both slip and mechanical twinning occurs during the placement of Vickers microhardness indentations. The occurrence of plastic deformation in this normally brittle material is considered to be a consequence of the nature and magnitude of the local stresses developed under pointed indenters and irregularly shaped abrasive particles. Preliminary results on the effect of annealing on the retained substructure are also presented. Annealing at 900°C and higher resulted in the reduction of residual stresses through the motion of dislocations and their rearrangement into lower-energy configurations.

Analysis of thermal elastic-plastic stress and strain during welding by finite element method

Abstract: It is well known that welding thermal stresses and resulting residual stresses influence the strength of welded construction, causing troubles such as brittle fracture, buckling and weld cracking. At the instant of welding, a limited portion of the welded joint is heated up to a very high temperature and cooled down to room temperature. In the thermal cycle which takes place, the temperature distribution changes with time and it affects the mechanical properties of the metals. In order to perform a reliable theoretical analysis, the above mentioned factors should be taken into account. The authors developed a method of theoretical analysis of this problem based on the finite element method, with consideration of the effects of changes in the modulus of elasticity, yield stress and the coefficient of linear thermal expansion of the metal with temperature. They analysed thermal transient stresses induced in a butt weld under a moving electrode and also in a fillet weld in the courses of the first and second beads and obtained various information on thermal stress history in the process of welding. Examples verifying usefulness of the method are cited.

Effect of joint geometry on the toughness of epoxy adhesives

Abstract: Increasing joint thickness was shown to increase the toughness of epoxy joints hardened with either tetraethylenepentamine (TEPA) or hexahydrophthalic anhydride (HHPA) The increased toughness was associated with a marked increase in macroroughness An upper limit of joint thickness and hence toughness occurred because very thick joints could not be produced Residual stresses developed during cooling from the curing temperature caused the latter to separate at the interface Stress corrosion cracking resistance was also found to depend on bond thickness For the TEPA-hardened system, bond thickness had only a minor influence for thicknesses up to 25 mils; and for the HHPA-hardened system, this persisted to bond thickness of 50 mils Further increases in bond thickness for both systems caused an abrupt rise in resistance to stress corrosion cracking

A magnetic method for the determination of residual stress

Abstract: A magnetic method for the measurement of residual longitudinal stress in the outer portions of cylindrical bars is developed and applied to nickel and steel. It involves measurement of the reversible effective permeability over a range of frequency of the applied alternating field. Special composites specimens, in which any desired level of residual stress can be produced, serve as idealized test specimens. Magnetic stress measurements made on cold-drawn, machined and quenched rods are compared with measurements by X-ray diffraction and mechanical relaxation (slitting). A combination of magnetic and X-ray measurements yields qualitative information about the stress gradient in the outer portion of a bar.

Interfiber stresses in filamentary composites

Abstract: Theoretical and experimental results for the magnitude and distribution of interfiber stresses in a transversely loaded composite consisting of an elastic matrix reinforced with elastic fibers are presented. Interfiber stress distribution is also given for an in plane shear load condition. The mathematical model consists of uniformly spaced circular fibers in a square array. An approximate solution is obtained for the interfiber stresses. Theoretical results are compared with results of a photoelasticity investigation, Fil'shtinskii's rigorous elasticity solution for a plate containing rigid circular inclusions, and with results of a rigorous elasticity solution for a three-dimensional problem. The present approximate solution provides good agreement with the experimental results and with the theoretical results obtained by other authors. The method of solution presented can be used for predicting interfiber stresses in composites with various shape fibers arranged in arbitrary arrays, as well as for investigating interfiber thermal stresses, elasto-plastic deformations, and residual stresses.

Effect of Growth Parameters on the Residual Stress and Dislocation Density of Czochralski-Grown Silicon Crystals

Abstract: This paper discusses the effects of pull rate and rotation rate on the dislocation density and residual stress distributions in Czochralski‐grown silicon crystals. A photoelastic technique was used to study the residual stress. It was found that a pull rate of 7. 62 cm/h and a rotation rate of 12 rpm yielded a nearly ideal radial stress pattern and a relatively low and constant distribution of dislocations. In general, when the dislocation density increases from the center to the periphery, and the crystal has not undergone extensive plastic flow, an optical pattern indicative of a radial stress distribution is observed. Conversely, crystals which exhibit dislocation distributions that decrease toward the periphery and have undergone plastic flow show an optical pattern which indicates a departure from a radial stress.

Lamination residual stresses in cross-plied fiber composites

Abstract: Longitudinal and transverse residual stresses arising in lamination fabrication process of cross-plied fiber composites

The sensitivity of the superconducting transition temperature to residual stress in high-T c intermetallic compounds

Abstract: Residual-stress-induced superconductivity is reported to occur only in the high-T c members of the C14 and C16 crystal systems. Second transitions are also seen in ThIr2(C15) and MoRe3(A12). The change inT c , as a result of introducing large residual stresses, increases with the bulkT c .

Deformation and Fracture in Al-CuAl2 Eutectic Composites.

Abstract: Ambient temperature compressive stress-strain behavior to failure, and associated structural detail, have been characterized in Al−CuAl2 composites of small interlamellar spacing (≤2μ). Differences in the compressive and tensile yield stress levels of the composite are attributed to thermally induced residual stress. Analysis gives a residual tensile stress ∼3500 psi and anin-situ yield stress ∼13,500 psi in the aluminum-rich phase. Evidence for a dislocation-interface interaction is provided by the form of deformation substructure in the aluminum-rich phase. Failure in these multi-grained eutectic composites is shown to be controlled primarily by shear-mode buckling of the lamellar structure. Buckling leads to cleavage of the CuAl2 phase, shear in the aluminum-rich phase, accompanied by void formation, coalescence and crack formation.

Thermally induced residual stresses in eutectic composites

Abstract: The effect of thermally induced residual stresses on the yield behavior of a unidirectionally solidified eutectic, (Co, Cr)-(Cr, Co)7C3 is presented. At low temperatures, the yield stress is found to depend on the sense of the applied stress. The difference in yield stress between tension and compression is a function of temperature and disappears at a sufficiently high stress relaxation temperature. A straightforward analysis is presented that predicts the observed yielding behavior and a stress relaxation temperature that agrees well not only with the value obtained by observing the temperature dependence of the yield stress, but also with the value obtained from the thermal expansion behavior of the eutectic composite.

The Effect of Load Interaction and Sequence on the Fatigue Behavior of Notched Coupons

Abstract: CONSTANT AMPLITUDE FATIGUE TESTS WITH VARIOUS CONDITIONS OF OVERLOADS WERE CONDUCTED TO UNDERSTAND THE EFFECTS OF LOAD INTERACTION AND SEQUENCE IN NOTCHED COUPONS. THE RESULTS WERE ANALYZED WITH PARTICULAR EMPHASIS ON THE LOCAL RESIDUAL STRESSES AT NOTCHES. FATIGUE LIFE RESULTS FROM THE TESTS HAVING A VARIATION IN THE NUMBER OF CYCLES BETWEEN THE PERIODIC OVERLOADS WHICH REINFORCE THE CONCEPT OF A FADING RESIDUAL STRESS. OTHER FATIGUE LIFE TRENDS COULD BE PREDICTED BY ASSUMING A STABLE RESIDUAL STRESS. CONDITIONS WHICH COULD CAUSE CYCLE-DEPENDENT OVERLOAD RESIDUAL STRESSES ARE DISCUSSED. AN EXPONENTIAL ANALYSIS FORM IS SUGGESTED FOR CALCULATING THE CYCLE-DEPENDENT LOCAL STRESSES FOR APPLICATION TO CUMULATIVE DAMAGE PREDICTIONS. /ASTM/

Prevention of residual stresses and orienta- - tion in thermoplastic injection mouldings

Abstract: In preventing stressing, the surface of the mould in contact with the injection moulding mass is partially heated before or after injection moulding. The surface is cooled when filling is completed. Pref. the temp. of the surface is raised to 20 degrees to 70 degrees C. esp. 50 degrees C., above the crystallite melting point.

Studies on Thermal Elastic-Plastic Problems (2 nd Report)

Abstract: It is well known that during welding or cutting, transient thermal stresses and strains are produced in steel structures and these residual stresses could be one of the causes of cold cracking in cooporation with diffusion of hydrogen and restraint rigidity of the structures. In this paper, a new calculation technique of residual stresses and strains due to welding is described.Thermal elastic-plastic stress analysis for one-dimensional problems has been studied for many years. In the previous paper, the authors reported the formulation of the finite element technique based on displacement method which could be applied to two or three dimensional thermal elastic-plastic stress problems. Recently, more complicated and realistic problems could be solved by using powerful numerical methods such as finite element technique, etc., because of the remarkable progress in computer application.On the contrary, the authors present a new calculation method which combines the idea of dividing the whole region into finite elements such as F. E. M. with the modified initial strain method and stress function introduced by Fujimoto. The above-mentioned stress function corresponds to the concept of the influence function studied by Kawai, and since this influence method is a sort of stress method, it is easily understood that the results calculated by this new method could show fair coincidence with the experimental data.It is comfirmed that thermal elastic-plastic stress analysis based on inherent strain method is rather effective compared with the finite element method of displacement type, when more accurate stress distribution is required, and also that calculation time would be much less when many incremental repetitions are needed.

The effect of cooling rate on the strength of brazed joints

Abstract: Experimental data are presented on the influence of cooling rate on the strength and deformation of thin Ag-4 pct Pd brazed joints in Fe-3 pct Si. It is observed that increasing the cooling rate (via water quenching vs furnace cooling) from the braze temperature can cause a drastic reduction in the strength of cylindrical butt brazed joints with a thickness to diameter ratio less than 0.02. The decrease in fracture strength is attributable to residual stresses and plastic strain caused by rapid cooling. The nature of the fracture process is unaffected by the cooling cycle and is always observed to be ductile failure caused by the growth and coalescence of microscopic shrinkage voids. Using hydrostatic annealing treatments, it is possible to restore the strength of rapidly cooled joints to values above those for furnace-cooled joints. This increase in strength is associated with a decrease in the volume fraction of microvoids accompanying the hydrostatic anneal.

Effect of Stress on the Physical Properties of Thin Films

Abstract: Residual stresses are almost always present in thin films; the magnitude of the stress (tensile or compressive) can be as small as 107 or as large as 1010 dyn/cm2. The stress in fine-grained polycrystalline films is generally isotropic in the plane of the film, and has no stress component perpendicular to the film plane. In such films there is then an isotropic strain in the film plane with a Poisson’s strain normal to the plane. For single crystal films the strain anisotropy will depend on the orientation of the film axes with respect to the substrate. In either case these strains induce an anisotropy and changes in the physical properties of the film. As examples of the effect of stress, the changes in magnetic and superconducting transition temperatures, and the induced magnetic, resistive, and optical anisotropies will be discussed.

Effects of loading sequence for notched specimens under high-low two-step fatigue loading

Abstract: The effects of loading sequence on crack-initiation period were investigated for notched aluminum-alloy specimens under high-low two-step loading with special emphasis on local cyclic stresses and strains at the notch root. Local stress and strain were determined by a procedure based on an equation proposed by Neuber which relates elastoplastic stress and strain at a notch. Local stress and strain were also measured experimentally to verify the Neuber equation. The effects of initial high load on the crack-initiation periods were demonstrated with notched specimens and were simulated in unnotched specimens fatigue tested with local stress sequences. An analysis of the results indicated that sequence effects were not caused solely by local residual stresses, as is usually assumed; the existence of a damaging effect, resulting from the high local strain cycles, was demonstrated. The sequence effects observed with notched specimens were interpreted as the combined result of residual stresses and high local strain cycles.

Stress relaxation as a source of dimensional instability

Abstract: Stress relaxation as source of dimensional instability in precision devices, discussing thermal cycling role in residual stress relief

On the studies of residual stresses in glass plates

Abstract: The theoretical foundation of the photoelastic methods being presently used for measuring and analyzing residual stresses in glass is insufficient for studying development of transient viscoelastic stress states in glass plates during tempering process and for an explanation of the actual material behavior. It is shown that the basic knowledge of photoviscoelastic effect in glass over a wide range of electromagnetic radiation and temperature is necessary for such on analysis. Some photoelastic properties of plate glass are presented.

Lamination Residual Stresses in Multilayered Fiber Composites.

Abstract: : Residual stresses arising from the lamination fabrication process are investigated using linear laminate theory. An equation to predict the residual stresses is given. The pertinent variables that influence residual stresses are identified. Several composite systems with various ply layup configurations are examined. Results are presented to illustrate the dependence of the residual stresses on the pertinent variables. The residual stresses are very sensitive to constituent material properties, composite stacking sequence and orientation, fiber content, and processing temperature. It is found that ply transverse tensile and in-plane shear residual stresses can reach magnitudes comparable to corresponding ply strengths and cause transply cracks in the composites. Residual stresses can also cause interply delamination. Ways to prevent transply cracking and interply delamination are recommended. (AN)

Experimental features of residual stress measurement by X‐ray diffractometry

Abstract: This paper is the second in a series of three which covers (1) theoretical considerations, (2) experimental features and (3) practical applications of X-ray diffractometer techniques to the accurate determination of residual macrostresses. The first paper appeared in the April 1970 issue of “Strain”.

Residual Stresses in Quenched and Tempered Plain Carbon Steels

Abstract: An investigation was made of factors contributmg to maximum compressive residual stress. Stresses from furnace hardening heat treatment were shown to be h~ghest at high hardness, medium carbon content, large section size, and minlmum hardenability over the range investigated. Shot peening was found to decrease high heat treatment stresses. A11 example showed very high fatigue strength m plain carbon steel at high hardness which was related to the very high compressive residual stress induced by severe water quenching during heat treatment. OVER THE LAST SEVERAL YEARS, studies have been made in the Research Department of Caterpillar IYactor Co., concerning the effect of residual stress on fatigue performance of steels and on the factors contributing to high compressive residual stress. Results of some of these investigations were discussed in a recent paper'. Effects on residual stress of variations i11 composition of plain carbon and some alloy steels, furnace hardening heat treatment, and cold wosking by shot peening were investigated. The influence of residual stress in fatigue was analyzed according to the theory of Fuchs', in which long life perfonnance is determined by resistance to csack initiation and/or propagation. This is an excerpt of some of the highlights from that paper concerning production of high compressive residual stress. An example is included showing the marked effect of residual stress on fatigue performance. Test Procedure Specimens used for the residual stress investigations were cylinders, basically of about 2-in. diameter and 6-111. length, of plain carbon and some boron steels. Chemical compositions of these along with the steels used in the fatigue tests are recorded in Tablc 1. The 0.25-in. radius circumferential notch was the smallest in which residual stress in the longitudinal direction could be measured by x-ray diffraction. The applied stress concentration factor in the notch was 1.5. All specimens were furnace heated and water quenched except the SAE 86B45 specimens, which were oil quenched. Fatigue specimens were finish ground in the notch after heat treatmcnt. Those to be used unpeened were electropolished in a bath of concentrated 60 per cent phosphoric plus 40 per cent sulfuric acids to remove the worked layer. Some cylindrical specimens were electropolished slightly to remove a decarburized or oxidized layer before surface stress measurement. Shot peening was done with 0.033-in. diameter shot for an intensity of about 0.024 in Almen A-2. TABLE 1 Chemical Compositions of Steels (Weight Per Cent) Element: C Mn R SAE No.