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Showing papers on "Necking published in 1986"


Journal ArticleDOI
TL;DR: In this article, the intrinsic stability of plastic deformation on the local scale has been examined with the help of standard methods of nonlinear analysis, such as yield points and the occurrence of necking, slip lines and slip bands also appear to be interpretable in terms of local instability of plastic flow.

200 citations


Journal ArticleDOI
TL;DR: In this article, the authors developed a model for deformation in an extending continental lithosphere that is stratified in density and strength, assuming a rheology consistent with seismic focal depths and experimental flow laws, showing that necking instabilities at two wavelengths will arise due to the presence of a strong upper crust and upper mantle separated by a weak lower crust.
Abstract: We develop a model for deformation in an extending continental lithosphere that is stratified in density and strength, assuming a rheology consistent with seismic focal depths and experimental flow laws. The model demonstrates that necking instabilities at two wavelengths will arise due to the presence of a strong upper crust and upper mantle separated by a weak lower crust. The magnitudes of the instabilities are directly related to strength contrasts within the lithosphere, while the dominant wavelengths of necking are controlled mainly by the thicknesses of the strong layers. The results are applied to the Basin and Range Province of the western United States where two scales of deformation can be recognized, one corresponding to the spacing of ranges and the other to the width of tilt domains. A Bouguer gravity anomaly and associated regional topography with a wavelength comparable to the width of tilt domains has also been recognized. For plausible density and strength stratifications, our results show that the horizontal scale of short wavelength necking is consistent with the spacing of individual basins and ranges, while that of the longer wavelength necking is consistent with the width of tilt domains. We thus suggest that Basin and Range deformation may be controlled by two scales of extensional instability. Extension in the weak lower crust in this model is laterally displaced from regions of upper crustal extension. The resultant horizontal shearing in the lower crust may be a mechanism for the initiation of low-angle extensional detachments.

133 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of material path dependent hardening on neck development and the onset of ductile failure is analyzed numerically using an elastic-viscoplastic constitutive relation that accounts for the weakening due to the growth of micro-voids.
Abstract: The effect of material path dependent hardening on neck development and the onset of ductile failure is analyzed numerically. The calculations are carried out using an elastic-viscoplastic constitutive relation that has isotropic hardening and kinematic hardening behaviors as limiting cases and that accounts for the weakening due to the growth of micro-voids. Final material failure is incorporated into the constitutive model by the dependence of the plastic potential on void volume fraction. Results are obtained for both axisymmetric and plane strain tension. Failure is found to initiate by void coalescence at the neck center in axisymmetric tension and within a shear band in plane strain tension. The increased curvature of flow potential surfaces associated with the kinematic hardening solid leads to somewhat more rapid diffuse neck development than occurs for the isotropic hardening solid. However, a much greater difference between the predictions of the two constitutive models is found for the onset of ductile failure.

96 citations


Journal ArticleDOI
TL;DR: In this paper, the conditions for which the initial disturbance will amplify as the lithosphere extends are evaluated for a range of rheological parameters, and the associated pattern of near-surface deformation is determined.

84 citations


Journal ArticleDOI
TL;DR: In this paper, the occurrence of highly deformed nuclei in the A approximately=80 and A approximately =100 mass regions has been investigated in the framework of the Strutinsky approach with a Nilsson-type potential and the Yukawa-plus-exponential macroscopic mass formula, including elongation, necking and gamma deformation.
Abstract: The occurrence of highly deformed nuclei in the A approximately=80 and A approximately=100 mass regions has been investigated in the framework of the Strutinsky approach with a Nilsson-type potential and the Yukawa-plus-exponential macroscopic mass formula, including elongation, necking and gamma deformation. Special emphasis was given to the spin-orbit potential parameters, which have large variations at the magic numbers and also depend on the shell filling. Good reproduction of the masses, deformations and shape transition was achieved in both mass regions. The phenomena of shape coexistence are also supported by the calculated potential energy surfaces. The odd-particle influence in driving the nucleus to deformed shapes is demonstrated. The results obtained are rather similar to those of the more elaborated Yukawa shell-model calculations, and show for the first time that a Nilsson-type model can also account for the large deformations of the light Kr, Sr and Zr nuclei.

45 citations


Journal ArticleDOI
TL;DR: In this paper, a model of cavity growth was introduced into the long wavelength approximation analysis which can describe the external neck development of specimens during deformation, and the results showed that both strain rate sensitivity m and cavity growth rate η have an important influence on the fracture strain of superplastic material.
Abstract: Necking development and fracture strain of superplastic material under tensile load are analysed by introducing a model of cavity growth into the long wavelength approximation analysis which can describe the external neck development of specimens during deformation. The results show that both strain rate sensitivity m and cavity growth rate η have an important influence on the fracture strain of superplastic material. According to these results, a fracture diagram is presented in m–η coordinates, which is divided into three: a region in which material fails by macroscopic external necking, a region where cavity growth is predominant leading to fracture without pronounced external necking, and an intermediate region where both fracture modes occur. The prediction of fracture strain for various superplastic alloys exhibiting cavity growth during deformation is in good agreement with experimental results. The present analysis thus enables quantitative prediction of the effects of both strain rate se...

38 citations


Journal ArticleDOI
TL;DR: In this paper, a quasi-static neck propagation in polymers is studied for the case of plane strain tension, and a finite element solution characterizes the complete development of a neck in an initially smooth specimen.

38 citations


Journal ArticleDOI
TL;DR: In this article, the Cotterell's essential work of fracture (we) and the critical energy dissipation rate associated with the onset of crack extension were investigated, and it was shown that both measures are equivalent, at least under the plane stress conditions, and that they both represent the fraction of energy which is transmitted through the plastic deformation field into the crack tip region.
Abstract: Two measures of fracture toughness have been investigated. The first is the Cotterell's essential work of fracture (we) which reflects the energy absorbed in the process of localized necking and decohesion occurring within the crack tip region. The second is the familiar critical energy dissipation rate associated with the onset of crack extension and commonly designated by Jc. Total of 48 fracture tests have been performed on thin aluminum double-edge-notched panels and thin compact tension specimens with varying crack size-to-ligament ratios. In a simple experimental procedure it has been established that both measures are equivalent, at least under the plane stress conditions, and that they both represent the fraction of energy which is transmitted through the plastic deformation field into the crack tip region. The ratio “essential work of fracture/total work of fracture” has been suggested as a quantitative measure of the energy transmission process. Certain predictions are made concerning variations of the energy transmission factor (ETF) during the stable phase of ductile fracture propagation.

35 citations


Journal ArticleDOI
TL;DR: In this article, microstructural changes that take place in the plastic zone ahead of the crack tip are found to be more important in fracture than the microscopic processes immediately at the tip itself.

34 citations


Journal ArticleDOI
TL;DR: In this paper, an analysis of necking development under uniaxial tensile deformation is made to derive the analytical expression for the correlation between the elongation e f to failure, the strain rate sensitivity m and the strainhardening effect n for geometric defects as follows: e f = {1−(1−f) 1 m } −m exp (n)−1 This expression is in agreement with the m-e f relationship given by Ghosh and Ayres where n = 0, or with the classical analysis of Considere where m = 0.

29 citations


Journal ArticleDOI
TL;DR: In this article, a uniform drawing of polyethylene mat was shown to destroy the two-phase structure made up of alternately stacked crystalline and amorphous regions and then reorganize it into a single-phase crystalline structure.
Abstract: Single-crystal mats of ultrahigh-molecular-weight polyethylene can be drawn uniformly to high draw ratios, more than 20χ at the highest, after the necking process is completed. The dynamic mechanical modulus of the drawn mats increases markedly during the uniform drawing stage. The structural changes induced by the uniform drawing at 100°C have been followed by wide-angle and small-angle x-ray scattering, infrared absorption, differential scanning calorimetry, and birefringence. The crystallinity is estimated from the x-ray amorphous scattering intensity, the IR absorbance of gauche bands, the heat of fusion from DSC, and the density. The estimated crystallinities of the drawn mats are all very high and increase slightly and monotonically with increased drawing after necking, though the values of the crystallinity depend on the method of estimation. IR gauche bands and the SAXS peak due to the long period disappear at a draw ratio of about 80χ. All the results suggest that the uniform drawing after necking destroys the two-phase structure made up of alternately stacked crystalline and amorphous regions and then reorganizes it into a single-phase crystalline structure.

Journal ArticleDOI
TL;DR: In this article, a bifurcation analysis of a solid composed of alternating material layers is carried out, and conditions under which periodic incremental deformations (eigenmodes) consistent with an overall homogeneous stretching, can emerge when the solid is subjected to plane strain, uniaxial tension parallel to the layer interfaces.

Journal ArticleDOI
TL;DR: In this article, the authors studied the deformation and fracture between a pair of holes in an infinite plate submitted to uniaxial tension in order to gain insight for the mechanism of ductile fracture.

Patent
30 Apr 1986
TL;DR: In this article, a melt-spinning process for polymeric filaments at a spinning speed controlled by a positive mechanical withdrawal is described, whereby a drawing and necking down of the filaments occur below the spinning pack.
Abstract: A melt-spinning process for spinning polymeric filaments at a spinning speed controlled by a positive mechanical withdrawal means that increases the speed of the filaments to above 7,000 meters/minute whereby a drawing and necking down of the filaments occur below the spinning pack, directing a gas into a zone extending from the spinning pack to a location between the spinning pack and the withdrawal means, maintaining the zone under superatmospheric pressure of less than 0.03 kg/cm2 and increasing the velocity of the gas as it leaves the zone to a level greater than the velocity of the filaments to reduce the extent of necking down of the filaments.

Journal ArticleDOI
TL;DR: In this paper, the authors extended the Bridgman analysis of tensile necking to obtain stress-strain data beyond the point of onset of necking from a split Hopkinson bar.
Abstract: The objective of this effort was to extend the Bridgman analysis of tensile necking to obtain stress-strain data beyond the point of onset of necking from a split Hopkinson bar. For this purpose, combined analytical and experimental techniques were considered. The analytical efforts were focused on validating the use of Bridgman solutions for high rate of deformation through a finite-element analysis of a tapered tensile specimen. The experimental technique involved the development of a photographic system using a light-emitting diode and a 35-mm rotating drum camera for the observation of necking during dynamic tensile tests conducted with a split Hopkinson tension bar. The developed new technique was successfully used to measure neck profiles of 6061-T6 aluminum, HY100 and 1020 steel tensile specimens. The measured profiles were used with the Bridgman analysis and stress-strain data were obtained to over 70-percent strain.

Journal ArticleDOI
TL;DR: In this paper, an equation of state with the densities of mobile and immobile dislocations as structure parameters is proposed to describe the evolution of dislocation structure and a mathematically simple model is then used to compare the stable and unstable modes of deformation.

Patent
07 May 1986
TL;DR: In this article, a rolling tool was fitted into a bottomed cylindrical can and the outside periphery of the can was worked in the direction P from the opening part 2 side to the vicinity of a bottom part 4.
Abstract: PURPOSE:To raise a design effect by giving comparatively large deformation to a metallic can, by performing successively necking and curling to an opening part of a bottomed cylindrical metallic can, and thereafter, pressing a rolling body against the drum part, and performing rolling in the longitudinal direction of the can CONSTITUTION:Necking and curling are performed successively to the vicinity of an opening part 2 of an Al can 1 formed in a bottomed cylindrical shape by impact extrusion, and thereafter, a vertical rib 6 is rolled to the outside periphery of the can 1 When executing the rolling, a rolling tool 3 which had detached an inner ring from a deep groove type radial ball bearing is fitted into the outside periphery of the can 1, and the outside periphery of the can 1 is worked in the direction P from the opening part 2 side to the vicinity of a bottom part 4 In this regard, as for the can 1, after the curling or the rolling, drawing is performed to the drum part as necessary In this way, comparatively large deformation is given to a metallic can and a deformed can having a high design effect can be manufactured

Journal ArticleDOI
TL;DR: In this paper, the effects of deformation temperature and additions of impurity elements on the ductility of solution-treated 25Cr-20Ni steels have been examined at the relatively high strain rate of 0·11 s−1 by means of hot tensile tests.
Abstract: The effects of deformation temperature and additions of impurity elements on the ductility of solution–treated 25Cr–20Ni steels have been examined at the relatively high strain rate of 0·11 s−1 by means of hot tensile tests. The ductility v. temperature curve can be divided into three regions: region I, 1000–1200 K, where there is a ductility minimum due to M23C6 precipitation on grain boundaries; region II, 1225–1400 K, which exhibits a plateau or a slight trough of ductility with corrugated boundaries as a result of dynamic recrystallization localized near the boundaries; and region III, 1450–1600 K, where recrystallization through the whole specimen leads to ductile fracture with complete necking. It was also confirmed that the grain boundary segregation of Sb and S and the sulphide precipitation on the grain boundaries accelerate intergranular cracking and reduce ductility in the range 1075–1300 K, and that, because sulphide particles melt on boundaries, the zero ductility temperature is marke...

Journal ArticleDOI
TL;DR: In this article, a rate-type formulation of quasi-static boundary value problems using convected material frames is proposed and an associated method of numerical solution is derived, and two numerical problems are presented: the first deals with a significant validation example, the second with a necking bifurcation analysis.
Abstract: A rate-type formulation of quasi-static boundary value problems using convected material frames is proposed and an associated method of numerical solution is derived. Two numerical problems are presented: the first deals with a significant validation example, the second with a necking bifurcation analysis.

Journal ArticleDOI
TL;DR: The use of the Minimat miniaturized materials testing machine for the testing of plastics is discussed in this article, where the instrument shows great flexibility and a wide range of material parameters relevant to tensile, compressive, fracture and toughness behaviour can be measured.


Journal ArticleDOI
TL;DR: In this article, a set of contiguous alpha grains aligned in the rolling direction caused local variations in the flow stress, strain to necking, strain rate sensitivity, plastic strain ratio values and surface roughness.
Abstract: Sheet tensile test pieces were machined in three orientations from edge textured Ti-6Al-4V bar and tested at temperatures in the range 800 to 975‡ C and at strain rates of 3 × 10−4 and 1.5×10−3 sec−1. Bands of contiguous alpha grains aligned in the rolling direction caused local variations in the flow stress, strain to necking, strain rate sensitivity, plastic strain ratio values and surface roughness. Texture effects were only detected at the lowest test temperature (800‡C) and highest strain rate (1.5×10−3 sec−1).

Journal ArticleDOI
TL;DR: In this article, the characteristics of serrated flow (onset strain, necking behaviour and angles of inclination of the stretcher-strain markings) were investigated by determining the dependence of these characteristics on the orientation of thin sheet tensile samples which had been deformed by different amounts of cold working.

Patent
02 Jul 1986
TL;DR: In this paper, a cylindrical shape for checking a necking deformation is inserted into the non-product part provided at the pipe end part of a circular pipe and this is held by the chuck 3 to which the end face of the circular pipe P is abutting.
Abstract: PURPOSE: To perform the necking of a circular pipe without causing any crack, etc., in a short time by inserting the die to prevent the drawing deformation into the pipe end part of a circular pipe and drawing with a drawing tool the boundary part of the product part and non-product part of the circular pipe with rotating it. CONSTITUTION: The die 1 of a cylindrical shape for checking a necking deformation is inserted into the non-product part P 1 provided at the pipe end part of a circular pipe P and this is held by the chuck 3 to which the end face of the circular pipe P is abutting. The product part P 2 of the above circular pipe P is held by a chuck 2 and the pipe P is rotated by driving it with the above die 1. In this state, the roller 4 freely rotating around a rotary shaft C is pressed to the boundary part B of the above product part P 2 and non-product part P 1 and yet with reciprocatingly moving in the horizontal direction, it is gradually advanced to draw the pipe P of the boundary part B. The pipe P is thereafter cut at the minimum diameter part A of the above necking part, the non- product part P 1 is removed and the product part P 2 whose pipe end part is drawn in the aiming shape is obtd. COPYRIGHT: (C)1988,JPO&Japio

01 Mar 1986
TL;DR: In this paper, strong discontinuities across quasistatically propagating surfaces in anisotropic elastic plastic solids under generalized plane stress have been reexamined allowing for some generality in constitutive response and taking into account the phenomenon of necking.
Abstract: : Strong discontinuities across quasistatically propagating surfaces in anisotropic elastic plastic solids under generalized plane stress have been reexamined allowing for some generality in constitutive response and taking into account the phenomenon of necking. Jumps in stresses have been ruled out on the basis of material stabiltiy postulates and a previous approach has been discussed. It has been noted that for elastic-perfectly plastic solids, sliding velocity discontinuities occur under restrictive and exceptional conditions (when both the surface and its normal are stress characteristics) for generalized plane stress as compared to plane strain. Necks may form along (stress) characteristic directions with the relative velocity vector orthogonal to the other family of characteristics.

Patent
10 Mar 1986
TL;DR: In this article, a method to detect high tension in a web material being taken-up and cutting off the take-up device upon such detection to prevent stretching and necking of the fabric being handled.
Abstract: Apparatus and method to detect high tension in a web material being taken-up and cutting off the take-up device upon such detection to prevent stretching and necking of the fabric being handled. The detection device provides a time delay between detection of the condition of high tension and deactivation of the fabric take-up apparatus.

Journal ArticleDOI
TL;DR: In this paper, low temperature tensile properties of microduplex stainless steel having different hardness of ferrite phase were investigated by means of transmission electron microscopy and X-ray diffraction.
Abstract: Low temperature tensile properties of microduplex stainless steel having different hardness of ferrite phase were investigated by means of transmission electron microscopy and X-ray diffraction. The hardness of ferrite in duplex stainless steel was changed by heat treatment.The main results obtained were as follows;(1) The austenite phase in the microduplex stainless steel was metastable. Therefore, martensite transformation was induced during tensile tests below room temperature.(2) The elongation to fracture showed a peak at 201K in the elongation-test temperature curves. This phenomenon is closely related to the amount of strain necessary to induce α' martensite, the amout of α' martensite and the ductility of the ferrite phase.(3) A discontinuity in flow stress-strain curves, namely the quasi-yield point phenomenon, was found buring tensile tests at 77K. This phenomenon seems to be associated with both necking arising from the formation of e martensite and strengthening of that portion due to the formation of α' martensite.(4) Md temperature was unchanged in spite of the variation of ferrite hardness in the duplex stainless steel. This fact may suggest that the deformation of ferrite and austenite phases follows the rule of mixture.

Journal ArticleDOI
TL;DR: In this article, the constitutive functions of deformation, work hardening rate, H, and deceleration, D, are specialized for various deformation paths, and related to the evolution of dislocation structure.
Abstract: The constitutive functions of deformation, work hardening rate,H, and deceleration,D, are specialized for various deformation paths, and related to the evolution of dislocation structure. Based on the variation with deformation ofH andD it is shown that two modes of tensile deformation may be defined: a destabilizing mode which leads to the normal homogeneous deformation behaviour terminated by necking and rupture, and a stabilizing mode which gives rise to Luders band formation and subsequent homogeneous deformation. The conditions for Luders banding are established and a simple mathematical description based on these concepts is given. A detailed discussion shows that with theories using only one structure parameter it is not possible to understand the Luders phenomenon.

Journal ArticleDOI
TL;DR: In this article, experimental results concerning the forming limit of in-plane stretching of brass, copper, and aluminum sheet alloys are presented, and theoretical curves of limit strains are calculated on the basis of the modified M-K (Marciniak and Kuc'zynski) analysis in which the analysis is applied to the post-diffuse necking (post-instability) condition.
Abstract: Experimental results concerning the forming limit of in-plane stretching of brass, copper and aluminum sheet alloys are presented. Theoretical curves of limit strains are calculated on the basis of the modified M-K (Marciniak and Kuc'zynski) analysis in which M-K analysis is applied to the post-diffuse necking (post-instability) condition. The imperfection is represented by the apparent initial inhomogeneity factor, f, as estimated from the ratio of the minimum to maximum thickness of the sheet at the instability condition, which is equal to unity at plane-strain condition and then decreases with an increase of strain ratio. It can be concluded that the predicted limit strains depend on the work hardening law equations applied and, when best fit work hardening law equations for the materials, namely Voce, Swift, and Hollomon law equations for brass, copper, and aluminum, respectively, are applied, the predicted limit strains are in food agreement with the experimental data plots. These results are explained in terms of the work hardening behavior.

Patent
12 Mar 1986
TL;DR: In this paper, the two parts are then assembled by magnetic forming in such a manner that the necking of one part around the other is propagated in the form of a wave along a necking zone.
Abstract: This lug is composed of a first metallic part (12) comprising means (16, 18) for junction with an electrical terminal and of a second metallic part (14) comprising means (22) for junction with one end of an electrical cable. The first part (12) is made from copper or a copper-based alloy and the second part (14) is made of aluminium or an aluminium-based alloy. The two parts are then assembled by magnetic forming in such a manner that the necking of one part around the other is propagated in the form of a wave along the necking zone.