Showing papers on "Necking published in 1985"

Method and apparatus for necking and flanging containers

Abstract: A modular system for producing triple-necked open ended containers includes three substantially identical necking modules each having the same frame and identical rotatable turrets which have a plurality of identical necking stations around the periphery. Each necking station includes an annular necking die and a platform and punch which are cam-operated to move towards and away from each other and are maintained in engagement with the cams by pressurized fluid. Each necking station also has a container pressurizing means in the form of an annular chamber which acts as a holding chamber prior to transmitting the pressurized fluid into the container.

Analysis of necking and neck propagation in polymeric materials

Abstract: N ecking and neck propagation as observed in polymers which “cold draw” is analyzed numerically for a circular cylindrical tensile specimen. The entire load-deformation history of the bar is computed using the finite element method in conjunction with hill's (1958, 1959) variational principle. Rate-independent elastic-plastic material behaviour is assumed. Results are given for the overall load-elongation response of the bar, as well as for the evolution of the specimen profile and the stress and strain distributions in the bar at various stages of the deformation process. The implications of our results on conventional methods used to analyze tension data for polymers are also discussed.

Effects of plastic anisotropy and yield surface shape on sheet metal stretchability

Abstract: The influence of plastic anisotropy and the shape of the yield surface on localized necking of thin metal sheets is examined Forming limit curves (FLCs) of strain hardening, rate-sensitive sheets including Ti alloys, Al alloys, and steels are calculated on the basis of the Marciniak-Kuczynski approach using the quadratic Hill or the Drucker yield function in conjunction with either the flow or deformation theory of plasticity The roles of the R-value and the yield surface shape in biaxial stretchability of sheet metals are delineated and discussed in relation to the plasticity theories and yield functions It is concluded that the limit strains decrease with increasing R-value in the e2 > 0 region of an FLC but increase with the R-value in the e2 0 region, and are independent of the R-value at plane strain conditions These mixed, strain-path dependent effects are explained in terms of the shape of the yield surface and a recently proposed critical thickness strain criterion

A simplified numerical analysis of the sheet tensile test

Abstract: A simplified numerical analysis of the tensile test for sheet metal specimens is presented with particular emphasis on the relationship between plastic flow parameters and tensile ductility. This analysis is based on a one-dimensional, “long wavelength” approximation in which the stress state is assumed to be uniaxial throughout the deformation. To account for the influence of necking and triaxiality on the flow behavior, however, an extended Bridgman correction for sheet specimens deformed under conditions of plane stress is employed. The governing equilibrium equation and boundary conditions are discretized to obtain computer solutions. Engineering stress-strain curves and strain distributions in deformed tensile specimens are compared to results from a more complex formulation previously published in the technical literature and show good agreement with it.

A new density of states model of BaPb1−xBixO3

Abstract: A systematic comparison of various has revealed that a simple-band concept is a good approximation but in a rather limited compositional range near x = 0.1. A new band model, which considers a local instability of -Bi-Bi- pairs against the charge disproportional, i.e. -Bi(I)-Bi(II)- is proposed in the metallic range in order to explain the deviations of the observed parameters from those expected from the simple model. It is suggested that a precursory effect of the metal-to-insulator transition at x = 0.35 sets in well in advance and causes a “necking” of the density of states at the Fermi level.

An analysis of the nonisothermal tensile test

Abstract: An analysis of the uniaxial tensile test which includes the effects of heat generation and transfer on flow behavior is presented. The analysis is based on the solution of modified versions of the onedimensional force equilibrium and heat conduction equations, subject to the appropriate boundary conditions. The stress biaxiality or triaxiality developed during necking is taken into account by including a Bridgman correction in the equilibrium expression. In order to obtain solutions of the coupled deformation-heat transfer problem, the governing equations were discretized to enable numerical calculations using a finite-difference scheme. The accuracy of the analysis was confirmed by comparison of model predictions with experimental data from nonisothermal tensile tests on 1008 aluminum-killed sheet steel. These and other simulations lead to the conclusion that temperature effects are most important following the onset of necking. The development of temperature gradients during necking can substantially decrease the tensile elongation and mitigate the stabilizing influence of positive strain rate sensitivity.

Method and device for necking work

Abstract: PURPOSE:To generate no wrinkle of a neck part, and to enlarge a neck-in depth by rotating a cylindrical body to be worked, drawing an inclined reduced diameter part in the diagonal upper direction between an external die and an internal die, and executing a necking working. CONSTITUTION:A necking working part 5 having a neck end forming surface part 6 formed so as to increase gradually an overhang quantity (m), a pressing surface part 7 and an inclined downward surface part 8 is provided on an inside surface of an external die 2, a die frame 10 is installed to a supporting shaft 9, and an internal die 3 is formed. Subsequently, an outside surface of an opening end of a cylindrical body to be worked (a) is pressed down against the pressing surface part 7 by a drum part pressing part 11 of the die frame 10, the cylindrical body (a) is rotated by a lifting body 27, a neck taper forming part 13 of the die frame 10 is moved to the inside and also in the diagonal upper direction along the surface part 8 in accordance with an overhang quantity (m) of the surface part 6, and it is formed, drawing a neck tapered part of the opening end of the cylindrical body (a). In this way, no wrinkle is generated in the neck part, and the neck-in depth can be enlarged.

Method of forming bottomed cylindrical bodies from a cylindrical body of thermoplastic resin

Abstract: A method of forming bottomed cylindrical bodies, which can be used conveniently as preforms for the production of containers by stretch blow-molding, etc., from a cylindrical body of thermoplastic resin. The method includes a softening step of heat-softening an axially intermediate part of the cylindrical body, a necking step of necking the axially intermediate part of the cylindrical body radially inwardly, said necking step being carried out subsequently to, or simultaneously with, the softening step, a cutting step of cutting the axially intermediate part of the cylindrical body necked radially inwardly in the necking step, thereby to divide the cylindrical body into two members, and a fusing step of heat-melting the cut end portion of each of the two members and fusing the cut end portion.

High Strain Rate Material Behavior

Abstract: : High strain rate material behavior of 1020, C1008, HY100 steels, OFHC copper, 7039-T64 aluminum, and BeO was characterized. Data were obtained from split Hopkinson bar (SHB) and plate impact test configurations. A high speed photographic system was used to obtain dynamic stress-strain data from necking Hopkinson bar specimens. The state variable based viscoplastic constitutive model of Bodner and Partom was considered for the material modeling. Computer programs and special purpose subroutines were developed to use the Bodner-Partom model in the STEALTH finite difference code. A unique iterative algorithm was developed to evaluate the model constants from both tensile SHB and plate impact test data. The model constants were determined for the five metals. Both tension and compression SHB and plate impact tests were successfully simulated using Bodner-Partom model constants.

Bifurcation in compressible elastic/plastic cylinders under uniaxial tension

Abstract: The bifurcation problem of a circular cylinder of elastic/plastic material under uniaxial tension is investigated, with particular reference to the usual engineering criterion that necking is initiated when the load on the specimen reaches a maximum. The material considered is compressible, with a smooth yield surface and associated flow rule. A lower bound analysis shows that for the particular constitutive equation chosen bifurcation cannot occur under a range of loading conditions while the stress is less than a certain value which is itself slightly less than the stress at the maximum load point. Diffuse axisymmetric necking modes under the commonly assumed loading conditions of prescribed axial components of velocity and shear-free traction-rates on the ends are, however, found to be initiated always after maximum load, the delay depending on the same factors shown for an incompressible material in reference [1]. The effect of the elastic compressibility assumption is to reduce the delay for a wide range of geometries, but to increase it for very slender specimens, as compared with the incompressible case. Surface modes are also found, but at stresses of an unrealistically high order of magnitude.

Energy Structure of Localization

Abstract: It is shown that a great number of physical objects with localized energy are described by theories with the same mathematical structure: the energy is the sum of two terms – one is a nonconvex functional of field variables and other is a quadratic functional in their gradients. The following examples are considered: bending of rods, dimples in shells, vapor bubbles in a liquid, necking, solitary waves, elementary particles, dislocations.

Method for drawing heavy wall shells

Abstract: A forming machine (10) is provided for forming a finished part (12) from a flat blank (14). Draw stations (18-24) are provided to initially form the intermediate part. Each draw station includes a punch (44, 62, 66, 70) and a draw die (48, 64, 68, 72). Each punch defines a shoulder along its length to create a step (60) in the side walls (26) of the intermediate part. In the subsequent necking and final form stages (30, 32, 34) the punch employed also has a shoulder to permit variation of the force applied to the intermediate part between the step and bottom portion.

Dilatational plastic constitutive equations and their application to ductile fracture analysis of axisymmetric specimens

Abstract: In many ductile materials voids nucleate and grow under large strain and triaxial stress, which yield volumetric plastic expansion. A constitutive equation is presented, which accounts for this plastic dilatancy. The plastic moduli involved in this equation can be calibrated by using necking tests of axisymmetric bars, void model analysis and computer simulation. To verify the rationality of such a constitutive equation and adjust the values of plastic moduli, the constitutive equation with its moduli to be determined is applied to analyse the ductile fracture behaviour of axisymmetric bars.

On the influence of the coupling of thermal and mechanical processes in the necking problem in uniaxial tension

Abstract: After a brief summary of the general frame for the definition of constitutive laws of coupled thermomechanical processes, a formulation of a constitutive law for a particular material is introduced. This law is then applied to the uniaxial tension test using the finite element method. Theoretical and experimental results are compared. A particular investigation of the necking problem is presented.

Effect of Martensite-Austenite Constituent on Fracture Behavior of Weld Zone of HSLA Steel

Abstract: Fracture behavior of the weld zone of 80kg/mm2 class HSLA steel has been investigated by means of tensile test, Charpy impact test and three point bending test. The results obtained gave convincible evidences that showed the following important role played by the martensite-austenite (M-A) constituent on the initiation and propagation processes of cracks.For ductile fracture, cracks were initiated by cracking flaky M-A constituent or debonding blocky M-A constituent from ferrite matrix. Then cracks expanded to voids and developed to deep holes. The main crack was formed by coalescence of deep holes by internal necking and led to fracture of specimen with a ductile deep dimple fracture surface.On the other hand, for brittle fracture, cracks nucleated at the interface of blocky M-A constituent and ferrite matrix. Then the crack propagated into the specimen, resulting in catastrophic fracture with a brittle river pattern surface.

Instabilité et localisation de la déformation dans les monocristaux c.f.c.

Abstract: Single crystals of copper, aluminium and nickel oriented for single and multiple slip have been deformed in a tensile test at room temperature. The actual stress-strain curves and the plots of the slope da/dr versus the stress have been reported also beyond the necking point [math].It has been found that for single crystals oriented in direction at the onset of instability the [math] versus a curves beyond the necking point changes from a steeply decreasing slope into a horizontal branch. For orientation only, the [math] versus a curves develop a straight branches which are identical with the extrapolated ones in the range of [math].Shear bands from when the condition [math] is reached. Based upon the TEM and X-ray diffraction results, the formation of the shear bands has been related to the activation of the coplanar slip systems.

Analysis of Hot Tension Test Data To Obtain Stress-Strain Curves to High Strains

Abstract: High strain rate hot tension tests have been carried out on AISI 1020 (Unified Numbering System [UNS] G10200) steel using a Gleeble® testing machine. Tests have been terminated at a series of strains and the specimen geometries measured. From these measurements, local areas, strains, and strain rates are derived and are used to obtain the local true stress-true strain curves. These are corrected for the change in strain rate with strain using an equation of state. The corrected curves are in good agreement with published curves on similar steels determined by compression or torsion testing. Under the present testing conditions, the maximum strain to which correction can be applied is ∼ 1.5. This is imposed by the onset of rapid local deformation heating. Up to this strain, no stress correction of the Bridgmann type for necking appears to be necessary.

Biaxial Strength of HY 80 Steel

Abstract: The biaxial deformation behavior of HY 80 steel has been examined by testing thin wall tubes under combined axial tension and internal pressure. The effective stressstrain curves and the hardening response have been found to vary with the stress state. The plastic strain ratio at a given stress ratio deviates from the von Mises value except at the stress states near uniaxial tension, plane strain and equi-biaxial tension. Using Drucker theory, these deviations are eliminated and the resulting yield locus is in good agreement with both the Bishop-Hill theory and the experimental results. Influenced by the tube geometry, the instability strains at the onset of diffuse necking are decreased by an increase in hoop tension. The diffuse necking strains are reasonably predicted by the Swift and the LankfordSaibel/Mellor criteria.

Plastic Instability and Rupture Life in Tension Creep

Abstract: A conventional condition for the onset of necking in tensile creep is modified to include the strain rate dependence of the strain hardening rate. It is shown that rupture by necking can be ruled out in the stress range σ θo/N, the relation between calculated time-to-necking and the minimum creep rate resembles the well-known Monkman-Grant relation.

Perturbation solution of axisymmetric plastic problem I—Necking of a bar

Abstract: In this paper, basing on the general equations of axisymmetric plastic problems deduced in ref. [11], and employing perturbation technique, the asymptotic analysis for the necking problem is given. The result will provide knowledge of distribution of stress and strain in whole plastic region, thus, it will lead to a better understanding of the necking phenomena in a tension specimen, such as the cup-cone type fracture. I. Introduction The question of the stress and strain distribution in the neck formed under tension is complicated and it has not been fully solved. Since it is important to know the magnitudes of the flow stresses at the instant preceding rupture, this question attracts many investigators. Bridgman (1944) [~l, basing on the experimental data, assumed that the deformation was uniform across the minimum section, i.e. the radial velocity is proportional to r; hence the radial strain-rate ~, is equal to the circumferential strain-rate ~ 0 in the minimum section. It follows that ~,-~o there. Since the shape of the neck is unknown and can only be determined by tracing its gradual development, Bridgman supposed the profile of neck was circular arc, i.e. and assumed the radius of the curvature of the neck profile was