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Showing papers on "Necking published in 1982"


Journal ArticleDOI
TL;DR: In this paper, the lattice misorientation across the shear band, which is such to cause geometrical softening of the bands, is not sensitive to the imperfection form for high strength, low hardening crystals a comparison with existing experimental data shows remarkably good qualitative and quantitative agreement between the calculations and observations.

1,237 citations


Journal ArticleDOI
TL;DR: There are four distinct types of fracture in superplastic materials: failure by quasistable plastic flow, failure by necking, cavitation failure, and quasibrittle failure as discussed by the authors.
Abstract: There are four distinct types of fracture in superplastic materials: failure by quasistable plastic flow, failure by necking, cavitation failure, and quasibrittle failure. The characteristics of these four types are described with reference to experimental examples. Maximum elongation occurs in a superplastic material when it pulls out to a fine wire in quasi stable flow. It is demonstrated that there are two basic requirements for this type of flow: (a) a suppression of localized (but not diffuse) necking, and (b) a suppression of significant cavity interlinkage (but not necessarily of cavity nucleation and growth).

126 citations


01 Nov 1982
TL;DR: In this paper, the deformation and fracture behavior of P/M Ti and 6A1-4V alloys with porosity was studied, as well as the influence of hydrogen on the multiaxial deformation, fracture, and necking of sheet at negative minor strains.
Abstract: : Progress is reviewed for a research program which has examined the multiaxial deformation and fracture behavior of Ti alloys, particulary as influenced by impurities such as hydrogen and by microstructural defects such as porosity. The studies range from experimental and analytical modeling of critical fracture processes to structure-property studies of both wrought material in the form of sheet and powder fabricated material in bar form. Specifically the program has studied: (1) the modeling of ductile fracture through an examination of the deformation and fracture at isolated holes in plane-strain tension; (2) the deformation and fracture of P/M Ti and Ti-6A1-4V containing porosity; (3) the influence of hydrogen on the multiaxial deformation and fracture behavior of beta-phase (bcc) Ti-30V and alpha (hcp)-beta Ti-6A1-4V; and (4) the theory of localized necking of sheet at negative minor strains.

93 citations


Journal ArticleDOI
TL;DR: In this article, the authors used an elastic-plastic material model for a solid that develops a vertex on the yield surface, using representations of the uniaxial stress-strain curves found experimentally.
Abstract: F or long , ductile, thick-walled tubes under internal pressure instabilities and final failure modes are studied experimentally and theoretically. The test specimens are closed-end cylinders made of an aluminum alloy and of pure copper and the experiments have been carried out for a number of different initial external radius to internal radius ratios. The experiments show necking on one side of the tubes at a stage somewhat beyond the maximum internal pressure. All tubes, except for one aluminum alloy tube, failed by shear fracture under decreasing pressure. The aluminum alloy tubes exhibited localized shear deformations in the neck region prior to fracture and also occasionally surface wave instabilities. The numerical investigation is based on an elastic-plastic material model for a solid that develops a vertex on the yield surface, using representations of the uniaxial stress-strain curves found experimentally. In contrast to the simplest flow theory of plasticity this material model predicts shear band instabilities at a realistic level of strain. A rather sharp vertex is used in the material model for the aluminum alloy, while a more blunt vertex is used to characterize copper. The theoretically predicted bifurcation into a necking mode, the cross-sectional shape of the neck, and finally the initiation and growth of shear bands from the highly strained internal surface in the neck region are in good agreement with the experimental observations.

68 citations



Journal ArticleDOI
J.M. Jalinier1, J.H. Schmitt1
TL;DR: In this article, the forming limit of a material can be calculated through a two-slice sample assuming that: internal defects are equivalent to thickness defects, and the influence of the damage mechanism and the initial thickness of the sheet can be modeled.

46 citations


Journal ArticleDOI
TL;DR: In this article, the X-ray precession method was used to study stress induced products in single crystals of Ti-14 and 20 wt.% Mo alloys, showing that α martensite was formed in the portion of necking which appeared just after yielding.

41 citations



Journal ArticleDOI
TL;DR: In this paper, a study of the various parameters present in each method which may influence the strain localisation process indicates that the overall strain gradient across the bulged testpiece is responsible for the higher strain limits.

21 citations


Journal ArticleDOI
TL;DR: In this article, preoriented isotactic polypropylene was used to clarify the molecular process in zone-drawing with which the necking part is confined in a thin heating zone during uniaxial drawing.
Abstract: Preoriented isotactic polypropylene was used to clarify the molecular process in zone-drawing with which the necking part is confined in a thin heating zone during uniaxial drawing. The process was analyzed on the basis of rate process, the mechanical properties of zone-drawn samples, and the superstructural change during zone-drawing. The values of activation energy for deformation, ΔH*, and the activation volume, ΔV*, were affected by the deformation mechanisms preferentially taking place during the zone-drawing. The attainable maximum modulus of zone-drawn sample at θ = 45° was larger than those at θ = 0° and 90°. The highest strength was also obtained at θ = 45°. The values of modulus and strength strongly depended on both the orientation function of the crystal c-axis and the orientation function of amorphous chains. In the region of a very high zone-drawing rate, in which microcracks are preferentially formed, both modulus and strength decreased, whereas they increased with increasing the zone-drawing rate below this region, giving the optimum condition for achieving the maxima in the modulus and strength.

20 citations


Journal ArticleDOI
TL;DR: In this article, a plane stress constitutive relation for rigid-plastic sheets under biaxial stretching is presented, in which the yield surface expansion models the behaviour of a solid carrying a rounded vertex at the loading point.

Book
01 Jan 1982
TL;DR: In this article, the authors provide a background knowledge of steel behavior deep enough to allow the immediate prediction of steel response in most circumstances by engineers designing in steel, and provide a source of information and a unified background to steel.
Abstract: The purpose of this book is to bridge gaps that the author perceives as existing between structural engineers, metallurgists and students in those two professions. The book provides a background knowledge of steel behaviour deep enough to allow the immediate prediction of steel response in most circumstances by engineers designing in steel. It is relatively simple in its treatment but complex in its range, and provides a source of information and a unified background to steel. It is strongly biased to conventional steels and their application and covers the following topics: equilibrium, stability, buckling, structural systems and characteristics, statistical aspects of structures, structural failure, loads and load combinations, determinant and indeterminant systems, the upper and lower bound theorem, mechanical properties of steel, elasticity, shear stresses, stress-strain relations, plane stress and plane strain, yield conditions, plasticity, strain-rate effects, necking and ductile fracture, strain ageing, thermal effects, stress reversal, hardness, fracture, fatigue, fracture mechanics, notches, triaxial stresses, fracture initiation, cod (crack opening displacement), crack extension and propagation, pellini fad (fracture appearance diagram), steel manufacture, grain size, stainless steel, metallurgy, welding, electrodes, residual stresses, plates, stretching, drawing, forming, shear lag, fine, influence lines, matrix analysis, beams, universal sections, pipes, pressure vessels, columns, design codes, planning, economics and costs. The ISBN of the microfiche is 0 86910 078 5. (Author/TRRL)

Journal ArticleDOI
TL;DR: In this article, it was shown that the behavior of a rod subject to end couples is ruled by a nonlinear ordinary differential equation whose solutions describe the instability phenomena observed in severe bending tests of tubes, such as ovalization and necking of the cross section.
Abstract: In the framework of Antman's theory of elastic rods, it is shown that the behavior of a rod subject to end couples is ruled by a non-linear ordinary differential equation whose solutions describe the instability phenomena observed in severe bending tests of tubes, such as ovalization and necking of the cross section.

Journal ArticleDOI
TL;DR: The projection moire technique as mentioned in this paper affords an accurate method of measuring the geometry of the necked region in a tensile specimen and provides a self-consistent correction for triaxiality.
Abstract: The projection moire technique affords an accurate method of measuring the geometry of the necked region in a tensile specimen. Corrections to the measured stress, necessary to account for the triaxiality introduced by the neck, require values for the radius of curvature of the specimen at the minimum section. The spacing of fringes resulting from the interference between a grating projected on the specimen surface and a master grating not only provide information which permits calculation of the radius but also demonstrates any changes in symmetry resulting from plastic deformation. Results obtained by testing specimens of copper and mild steel having initially straight and initially curved profiles indicate that Bridgman's approach provides a self-consistent correction for triaxiality. However, comparison of incremental tests with continuous tests indicates that the development of neck geometry may be sensitive to the strain rate.

Journal ArticleDOI
TL;DR: In this article, the cold-worked NiTi and NiTi-Cu alloys in the martensite phase were investigated and it was shown that both have a higher elastic limit, a higher ultimate tensile stress and a different behaviour during the plastic deformation than annealed alloys.
Abstract: Recently, it has been shown that the cold-worked NiTi alloy has unusual pseudo-elastic properties in the martensite phase. In this communication further mechanical properties of NiTi and NiTiCu alloys in the cold-worked state are presented. It is shown that both have a higher elastic limit, a higher ultimate tensile stress and a different behaviour during the plastic deformation (i-e a large necking is observed) than the annealed alloys. These unusal mechanical properties have been explained in large part in terms of dislocation - dislocation and dislocation-martensite interface interactions. However some observed features are only understood if, in addition, the premartensitic phase (R-phase) is present and active during the phase transformation.

Book ChapterDOI
01 Jan 1982
TL;DR: In this paper, the reaction of a solid to continuously increasing applied tensile load is portrayed using a stress-versus-strain curve, and the Young's modulus, yield strength, ultimate tensile strength, percent elongation, and work hardening characteristics can be obtained.
Abstract: The reaction of a solid to continuously increasing applied tensile load is portrayed using a stress-versus-strain curve. From stress-strain curves the Young’s modulus, yield strength, ultimate tensile strength, percent elongation, and work hardening characteristics can be obtained. Typically, following the elastic deformation region, a metal or alloy work hardens at a decreasing rate until localized specimen necking initiates and the ultimate strength of the specimen has been reached.

Journal ArticleDOI
TL;DR: In this article, the effects of postcuring and plasticization by water and a non-volatile diluent dibutylphtalate was examined by conducting compression tests (at room temperature) and tensile tests.
Abstract: Post-yield behaviour, particularly strain softening, has been studied here for an epoxy resin to examine the effects of postcuring and plasticization by water and a non-volatile diluent dibutylphtalate. The significance of necking was examined by conducting compression tests (at room temperature) as well as tensile tests. In the case of tensile tests, elevated temperatures were used in order to achieve yielding. The amount of strain softening was found to be reduced by postcuring or by the addition of a plasticizer. In the case of postcuring, little change in yield stress occurred, whereas, with plasticizers, a reduction in yield stress does occur.

Journal ArticleDOI
TL;DR: In this article, the expression δ = K ϵ. m ϵ n has been adopted for the plastic flow of the sheet metal, for which expression Swift's criterion for diffuse necking has then been developed.

Journal ArticleDOI
TL;DR: In this paper, the authors present a summary of the results of study into the stress-strain relationship and ultimate strength characteristics of a SBS block copolymer (Cariflex TR-1200).
Abstract: The paper presents a summary of the results of study into the stress-strain relationship and ultimate strength characteristics of a SBS block copolymer (Cariflex TR-1200). The polymer has been investigated at uniaxial extension in the range of temperature from 20 up to 90 C. Two types of the stress-strain curves have been observed: S-shaped and the curves with a maximum corresponding to necking. The stress dependence on strain and lime can be factored as σ(e, t) = h(e) G(t). Viscosity has been measured. There exists a yield value of the stress above which it can be registered rather strong fall of viscosity. The yield value increases with decrease of temperature that is attributed to difficulties of break-down of the copolymer structure as temperature decreases. The long term durability of the block copolymer varies following a pattern typical of cured rubbers. The formation of specimens from solutions in various solvents may perceptibly affect this pattern, whereby the long term durability and t...

Journal ArticleDOI
TL;DR: In this paper, a structural pattern of the processes developing at different stages of the creep of PVC is proposed, based on the process of the local orientation rearrangement with formation of distinctive micronecks on reaching a certain critical concentration of which the macroscopic neck begins to form.
Abstract: Creep and necking processes of PVC have been studied using the direct structural methods: birefringence, X-ray structural analysis and electron microscopy. It is shown that the creep process is associated with the disruption of the supramolecular organization of the polymer. A structural pattern of the processes developing at different stages of creep of PVC is proposed. It is shown that the structural conversions on creep of PVC are based on the process of the local orientation rearrangement with formation of distinctive micronecks on reaching a certain critical concentration of which the macroscopic neck begins to form. The supramolecular organization of the polymer to the point of crystallites in the region of the neck is disrupted.

Journal ArticleDOI
TL;DR: In this article, it was shown that the anisotropy of products made of Zr-l% Nb alloy is caused by the reorientation of the grains of the material during tensile testing.
Abstract: the laws governing the formation of the properties of products. The anisotropy of plastic and strength properties of rolled zirconium alloys during tensile tests manifests itself in the different course taken by the process of deformation of specimens cut at various angles to the rolling direction. The action of plastic strain mechanisms is coupled with the regular reorientation of the grains of the specimen tested, as a result of which is the initial rolling texture. It is desirable to establish a correlation between the parameters of the stress--strain curve, recorded when the specimens are tested under tension in various directions, and the stability of their initial texture as well as to establish the distinction features in the changes in this texture during the testing. This correlation will make it easier to ascertain the causes of the anisotropy of the properties of products made of zirconium alloys and to develop methods of controlling this anisotropy. Experimental Procedure The specimens were made from cold-rolled tubing of Zr-l% Nb alloy with a diameter of 13.6 mm and a wall thickness of 0.9 ram. The tubing was cut along the generatrix and was straightened out. Tensile test specimens were cut from the resulting strips transversely and at 45 ~ to the rolling direction. The working part of the specimens measured i0 x 2 x 0.9 mm (series a) and 16 x 8 x 0.9 mm (series b). To remove the residual stresses which had arisen during the fabrication and straightening of the tubing the specimens were annealed at 500~ for 3 h in the presence of a getter in a sealed quartz ampul previously pumped down to 1.3.10 "a Pa. The specimens were tensioned in an Instron universal machine at a strain rate of 1.510 -4 sec -~. Longitudinal, transverse, and diagonal specimens of series a were loaded to breaking during recording of the load-extension diagram. The tensile diagrams obtained were replotted in the coordinates stress (o)--unit strain (~). The longitudinal and transverse specimens of series b were loaded until residual strains ~n of 6, 9, ii, and 4, 8, 12% were attained. The residual strains of the specimens of series b correspond to various segments of the stress~strain curve obtained on specimens of series a until necking occurred. The working part of the strained specimens of series b was cut out and subjected to x-ray examination in a DRON-I.5 diffractometer with CuK~ radiation.

Journal ArticleDOI
TL;DR: In this article, the development of a diffused neck has been observed during creep of recrystallized, commercially pure molybdenum, and the neck started already in the primary creep region but the creep rate did not increase; on the contrary, it continued to decrease and then stayed constant for a long period.

01 Oct 1982
TL;DR: In this paper, the applicability of mixture laws to two-phase steels is discussed, and the partititon of stress and strain between the soft and hard constituents is discussed.
Abstract: This paper discusses plastic deformation of two-phase alloys, the partititon of stress and strain between the soft and hard constituents, and the applicability of mixture laws. Dual-phase steels are considered in particular. At all strains, plastic deformation takes place mainly in the ferrite. The martensite resists plastic deformation at low strain but is ductile. The martensite particles supplies the desirable dispersion hardening effect, enhanced strain hardening rate and resistance to plastic instability such as necking, while yielding plastically at high strains. 12 figures. (DLC)


Book ChapterDOI
01 Jan 1982
TL;DR: In this paper, a theoretical and experimental study of interaction between cracks and voids leading to local internal necking is presented, based on the slip-line technique, and experiments on specimens of ductile commercial metals with prepared cracks.
Abstract: A theoretical and experimental study of interaction between cracks and voids leading to local internal necking is presented. The theoretical analysis of internal necking leading to the progressing ductile fracture has been based upon the slip-line technique. Experiments on specimens of ductile commercial metals with prepared cracks and voids substantiate the analysis.

Patent
18 Mar 1982
TL;DR: In this article, the authors propose to give shapes to the end of tin drums before the necking working is performed on them so that they will not touch necking tools during the course of working.
Abstract: PURPOSE:To reduce occurrencs of wrinkles and to prevent occurrences of flange crackings in the course of working, by giving shapes to the end of tin drums before the necking working is performed on them so that they will not touch necking tools during the course of working. CONSTITUTION:Beads 16 and 17 projected toward the outer surface of a tin drum are installed for a prescribed length at both sides of a side seam section 1 at the end of the tin drum, so that a protective film 14 of the side seam section 1 of the tin drum end will not touch to a die ring 7 or a center ring 10 of the necking tool. When the necking working is perfomed on a neck section 3 under this condition, problems, such as occurrences of rust at the cut edge, etc., due to exfoliatin of the protective film 14, concentration of stresses to the side seam section 1, etc., can be eliminated.

Journal ArticleDOI
TL;DR: The possibility of straining PETPH films in a direction perpendicular to the initial stretching axis has been demonstrated in this article, where it was shown that the change in mechanical character of the films corresponds to the structural rearrangement.
Abstract: The possibility of straining “silvery” PETPH films in a direction perpendicular to the initial stretching axis has been demonstrated. Stretching in the transverse direction proceeded uniformly without necking up to 3.5–4.0 times over a wide temperature range, from 30° up to the temperature corresponding to maximum crystallization. Structural changes in the transverse stretching process were studied and it was shown, moreover, that the change in mechanical character of the films corresponds to the structural rearrangement.

Journal ArticleDOI
TL;DR: In this paper, a theory was developed to calculate the necking load and to predict the strains that occur during extruding necks of cans or other cylindrical shells in dies.


Journal ArticleDOI
TL;DR: In this paper, the effects of both primary creep and necking are discussed and a brief comparison is made between failure criteria for cavitation failure and geometrical failure, where the former mechanism dictates the ultimate creep life of a material.
Abstract: Creep failure generally occurs either by the attenuative loss of area as flow proceeds (geometrical failure) or by the development of internal cavities. The former mechanism dictates the ultimate creep life of a material. Criteria are developed for this upper limit to life for a variety of creep mechanisms. The effects of both primary creep and necking are discussed and a brief comparison is made between failure criteria for cavitation failure and geometrical failure.