Showing papers on "Necking published in 1974"
TL;DR: In this article, the bifurcation problem governing the onset of axisymmetric necking in a circular cylindrical specimen in uniaxial tension is analyzed. But the authors do not consider the case where one end is subject to a prescribed uniform axial displacement relative to the other and both ends are shear free.
Abstract: The bifurcation problem governing the onset of axisymmetric necking in a circular cylindrical specimen in uniaxial tension is analysed. The specimen is made of an incompressible elastic/plastic material. One end is subject to a prescribed uniform axial displacement relative to the other and both ends are shear free. The true stress at bifurcation is greater than the stress at which the maximum load is attained by an amount which depends on (a) the radius to length ratio of the specimen, (b) the ratio of the elastic shear modulus to the tangent modulus, and (c) the derivative of the tangent modulus with respect to the stress. Bifurcation takes place immediately following attainment of the maximum load when the specimen is sufficiently slender.
135 citations
01 Jul 1974-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
Abstract: The onset of diffuse instability in sheet metals is associated with initially small, but grad-ually increasing, changes in the strain rate,e, and in the ratio of the minor to the major principal strains,p = e2/e1in the plane of the sheet. The hardening and softening contri-butions from such changes have been considered to obtain a condition for partial flow sta-biliity in the neck. The effect of the change ine on the uniaxial stress was determined from measurements of e changes in the neck and from the strain rate sensitivity of the materials. Similar evaluation of the change in the axial stress due to a change in p was made by means of an approximate analysis. The combination of these effects, along with the basic strain hardening of the materials, is used to explain the slowness or the rapid-ity of the process of necking in several materials, exhibiting different normal anisotropy, strain hardening and strain rate hardening behaviors. These results can also be used to explain the size of a diffuse neck and the strain distribution within it. Correlation has also been obtained between necking extensions to failure and the forming limits.
85 citations
TL;DR: In this paper, single crystal silver ribbons were strained to fracture with a precision tensile stage inside of a high voltage electron microscope and microstructural analysis of the basic ductile fracture mechanisms involved.
68 citations
TL;DR: In this article, the fracture process in rigid poly(vinyl chloride) has been investigated and a value of 1·05 × 10−3MN/m is obtained for the energy of formation of a new surface in undrawn material.
63 citations
TL;DR: In this article, the effects of plate thickness and stress ratio on crack tip deformation and fatigue crack growth in 2024-T351 aluminum alloy were studied and the authors derived the fatigue crack propagation relation da/dN = f(R) Delta K squared with three assumptions: small-scale yielding, material homogeneity, and that crack tip stresses and strains are not strongly affected by plate thickness.
Abstract: The fatigue crack propagation relation da/dN = f(R) Delta K squared can be derived with three assumptions: small-scale yielding, material homogeneity, and that crack tip stresses and strains are not strongly affected by plate thickness. The function f(R) is a constant at a given stress ratio, R. The effects of plate thickness and stress ratio on crack tip deformation and fatigue crack growth in 2024-T351 aluminum alloy were studied. High Delta K level in a thin specimen causes crack tip necking. Necking is more pronounced at high stress ratio. Necking causes high maximum strain near a crack tip and fast crack growth rate.
36 citations
TL;DR: In this paper, the authors measured the temperature rise of an oscillating neck of PETP films using an AGA Thermovision camera and found that the maximum surface temperature rise is very high, up to about 95° C and the temperature in the interior is probably higher.
Abstract: Extension of PETP films at constant rate of deformation may, under certain conditions, result in stress oscillation and a periodic necking. The periodic necking results in formation of transverse bands, alternately opaque and transparent, in the sample. In this study, the temperature rise of such an oscillating neck was measured using an AGA Thermovision camera. The measured maximum surface temperature rise is very high, up to about 95° C and the temperature in the interior is probably higher. The formation of the opaque zone starts in the centre line of the foil and spreads out to a maximum width during the advance of the neck. It then suddenly ceases without reaching the surface of the sample. The opacity is probably a secondary effect dependent only on the high temperature formed by dissipated energy from the necking process and not affecting the mechanism of self-oscillating necking.
23 citations
TL;DR: In this article, the interpretation of work softening on polycrystalline 99.95% Ni was carried out with the help of electron microscopy and it was proposed that work softens is an enhanced dynamic recovery effect.
17 citations
Patent•
24 Jul 1974
TL;DR: In this article, a method for producing a synthetic crystalline thermoplastic resin film suitable for stretching without necking was proposed, including adding 5 to 300 parts by weight of a filler to 100 parts of a synthetic polyethylene on isotactic polypropylene having a degree of crystallization of more than 60.
Abstract: A method for producing a synthetic crystalline thermoplastic resin film suitable for stretching without necking including adding 5 to 300 parts by weight of a filler to 100 parts of a synthetic crystalline thermoplastic resin film such as polyethylene on isotactic polypropylene having a degree of crystallization of more than 60%, pressing the film against a rigid blade having a radius of curvature of 0.01 to 1.0 millimeter, bending the film around the blade using the blade as a fulcrum to a bending angle between 20° and 170°, moving the film relative to the blade while keeping the bending angle constant thereby whitening the film, said whitening of the film being conducted without positively heating or stretching the film, and stretching the film after whitening at a draw ratio below the natural draw ratio of the film.
14 citations
TL;DR: In this paper, the discrepancies between the results obtained according to the two different procedures are outlined and discussed, and factors such as changes in the primitive defect structure, large variations ofm over the strain-rate interval covered and grain growth during deformation, are to be considered in explaining the origin of the discrepancies.
Abstract: The strain-rate sensitivity indexm of the Cu-9.5 wt % Al-4 wt % Fe alloy has been determined by two different procedures: (1) from a rate-change test and (2) from the slopes of the maximum engineering stress/initial strain-rate curve. The discrepancies between the results obtained according to the two different procedures are outlined and discussed. Besides the necking behaviour during deformation, factors such as (1) changes in the primitive defect structure, (2) large variations ofm over the strain-rate interval covered and (3) grain growth during deformation, are to be considered in explaining the origin of the discrepancies. Dunlop and Taplin's method is considered to be the better of the two procedures used for determiningm, since it introduces fewer errors. In this alloy, graincoarsening is caused by thermal activation as well as by the deformation process itself.
11 citations
TL;DR: In this paper, the necking condition for a material which transforms during tensile deformation is examined and an expression is developed which predicts the onset of plastic instability, which is shown to give results which are in good agreement with experimental observations obtained from a FeNi-C alloy.
10 citations
TL;DR: In this paper, it was shown that the limiting drawing ratio of the single-clad sheet of commercially pure hard aluminium and soft one changes from better value to worse one than that of each composing sheet, depending on the punch profile radius, the upper and lower side positions of a clad sheet and the ratio of thickness of each composition sheet.
Abstract: The purpose of this investigation is to make the deformation features of the clad sheet metals basically clear from a view point of its press formability. In the present paper, it is shown as an experimental fact that the limiting drawing ratio of the single-clad sheet of commercially pure hard aluminium and soft one changes from better value to worse one than that of each composing sheet, depending on the punch profile radius, the upper and lower side positions of a clad sheet and the ratio of the thickness of each composing sheet. The reasons for these changes are examined by considering the effect of bending conditions on the external surface strain, and the effects of the frictional force at punch profile surface and the traction force at the interface of each composing sheet on the stretching and necking deformation. General explanations for the experimental results are made by summarizing the change of these effects depending on the working conditions and the composing conditions.
TL;DR: In this paper, two conditions for stable necking, treated as a bifurcation of stress path, were derived for a thin cylinder under internal pressure, where the anisotropic material considered is one for which the plastic work increment = σ ¯ d e ¯, where both the generalized yield stress σ¯ and generalized plastic strain increment d e¯ are invariant functions.
01 Jun 1974
TL;DR: In this paper, the authors found that the generalized strain-hardening and the onset of necking were independent of back pressure and theoretical calculations of the maximum pressure differential agreed closely with experiment.
Abstract: Clamped aluminum circular blanks, having approximately planar isotropy, were bulge-formed by an oil pressure differential against hydrostatic back pressures of up to 69 MN/m2. Both generalized strain-hardening and the onset of necking were found to be virtually independent of back pressure. Theoretical calculations of the maximum pressure differential agreed closely with experiment. Theory underestimates the critical generalized strain at necking.