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Journal ArticleDOI

Stretchability of Prior Cold Worked AISI Type 304 Stainless Steel Sheet.

TL;DR: In this paper, the authors investigated the effect of prior cold work on the stretchability of type 304 stainless steel sheet and showed that for a substantial range of strain ratios from plane strain towards equibiaxial, sheets with lower levels of prior work show sharply increasing ductility.
Abstract: The article presents the results of an investigation of the effect of prior cold work on the stretchability of type 304 stainless steel sheet. The forming limit diagrams show decreased levels with increasing prior work. However, when the limits are plotted as total equivalent strain as a function of strain ratio, the ductility increases with prior cold work. Also, for a substantial range of strain ratios from plane strain towards equibiaxial, sheets with lower levels of prior cold work show sharply increasing ductility. The first observation is explained in terms of the adiabatic temperature rise and the temperature sensitivity of the strain-induced transformation (that occurs in type 304 stainless steel), which influences the strain hardening in the material. The second observation is understood in terms of the kinetics of the transformation, which depends on the state of stress. Finite element simulations using a model taking into account the strain-induced transformation also reveal many of the trends ...
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Journal ArticleDOI
TL;DR: In this article, the room temperature tensile properties of type 304, a metastable austenitic stainless steel, prior rolled above room temperature (200 °C and 300 °C) are compared with mill-annealed and material prior rolled at room temperature.
Abstract: In this study, room temperature tensile properties of type 304, a metastable austenitic stainless steel, prior rolled above Md temperature (200 °C and 300 °C) are compared with mill-annealed and material prior rolled at room temperature (25 °C). Strain-induced martensite that formed during the tensile tests, followed using in-situ using magnetic measurements, display kinetics that vary with prior deformation temperature and strain. Scanning Electron Microscopy and Electron Backscattered Diffraction studies provided direct evidence for shear band formation during prior deformation. Kinetics of strain-induced martensite is found to fit the Olson–Cohen equation modified to include the prior deformation strain and martensite formed during prior deformation. The systematic changes observed in the model parameters of the modified Olson–Cohen equation are explained. The strain hardening in the material is analyzed and correlated with changes in the rate of formation of strain-induced martensite with respect to strain.

3 citations

References
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Journal ArticleDOI
TL;DR: In this paper, it is shown that to answer several questions of physical or engineering interest, it is necessary to know only the relatively simple elastic field inside the ellipsoid.
Abstract: It is supposed that a region within an isotropic elastic solid undergoes a spontaneous change of form which, if the surrounding material were absent, would be some prescribed homogeneous deformation. Because of the presence of the surrounding material stresses will be present both inside and outside the region. The resulting elastic field may be found very simply with the help of a sequence of imaginary cutting, straining and welding operations. In particular, if the region is an ellipsoid the strain inside it is uniform and may be expressed in terms of tabu­lated elliptic integrals. In this case a further problem may be solved. An ellipsoidal region in an infinite medium has elastic constants different from those of the rest of the material; how does the presence of this inhomogeneity disturb an applied stress-field uniform at large distances? It is shown that to answer several questions of physical or engineering interest it is necessary to know only the relatively simple elastic field inside the ellipsoid.

11,784 citations


"Stretchability of Prior Cold Worked..." refers methods in this paper

  • ...Treating martensite as inclusions embedded in an austenite matrix, the equations relate the strain rate experienced by the martensite and the strain imposed on the austenite and are given by [30, 31]:...

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  • ...The additional relation required to uniquely determine the four rate quantities is obtained using Eshelby’s results [30]....

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Book
01 Jan 1950
TL;DR: In this paper, the solution of two-dimensional non-steady motion problems in two dimensions is studied. But the solution is not a solution to the problem in three dimensions.
Abstract: 1. Introduction 2. Foundations of the thoery 3. General theorems 4. The solution of plastic-elastic problems I 5. The solution of plastic-elastic problems II 6. Plane plastic strain and the theory of the slip-line field 7. Two-dimensional problems of steady motion 8. Non-steady motion problems of steady motion 9. Non-steady motion problems in two dimensions II 10. Axial symmetry 11. Miscellaneous topics 12. Platic anisotropy

7,810 citations


"Stretchability of Prior Cold Worked..." refers background in this paper

  • ...The relation for incremental equivalent strain is given below [34]:...

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  • ...Such a representation is due to the normality flow rule and is equivalent to specifying the limits in the principal stress space with the advantage that the constitutive equivalent stress–equivalent strain relation need not be known [7, 34]....

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  • ...In determining the equivalent strains, it is assumed that the material is isotropic and obeys Hill’s quadratic yield surface [34] and that the material is subject to linear strain paths during rolling and stretching....

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  • ...Assuming the von Mises criterion for the two-phase mixture to hold, the equivalent stress σ̄ is [34]:...

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Journal ArticleDOI
TL;DR: In this paper, a theoretical analysis of the process of the generation of the groove based on anisotropic plasticity theory is presented, and the system of equations derived was solved numerically with the aid of a computer, which enabled the limiting strain of the sheet metal to be determined as a function of the material.

1,814 citations

Journal ArticleDOI
TL;DR: In this paper, conditions for instability of plastic strain under plane stress for a material conforming to the Mises-Hencky yield condition and strain-hardening according to a unique relationship between root-mean-square values of shear stress (q) and incremental strain (δψ).
Abstract: This paper examines the conditions for instability of plastic strain under plane stress for a material conforming to the Mises-Hencky yield condition and strain-hardening according to a unique relationship between root-mean-square values of shear stress (q) and incremental strain (δψ). If, under fixed loading conditions, the material undergoes a strain increment which is consistent with the applied stress system, the conditions are stable or unstable according as the increment in representative yield stress is greater or less than the increment in representative induced stress. The strain at which instability arises is found in terms of the biaxial stress ratio p2/p1 under different conditions of applied loading, and the effect is demonstrated of strain-hardening according to an empirical relation of the type q = c (a + ψ)n. The analysis is also applied to certain cases of non-uniform stress distribution. In the case of the hydrostatic bulge results are obtained showing a critical thinning ranging from 26 per cent for a non-hardening material to about 45 per cent for typical strain-hardening materials, values in general agreement with experimental data. Conditions over the punch head in the pressing of a cylindrical shell are discussed but computations are not attempted.

1,604 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the permitted discontinuities of stress, velocity, and surface slope in a plastic-rigid sheet deformed in its plane, and the necessary restrictions on the stress-state and rate of workhardening were obtained for any yield function and plastic potential.
Abstract: Permissible discontinuities of stress, velocity, and surface slope are investigated in a plastic-rigid sheet deformed in its plane. One such discontinuity of velocity is shown to be the mathematical idealization of localized necking; the necessary restrictions on the stress-state and rate of workhardening are obtained for any yield function and plastic potential. The results are illustrated by an examination of the modes of necking in notched tension strips. The constraint factors at the yield point are obtained for notches with wedge-shaped or circular roots.

1,243 citations


"Stretchability of Prior Cold Worked..." refers background in this paper

  • ...The onset of flow instability depends on the instantaneous strain hardening rate, enhancing which, can postpone the onset of necking [1, 2]....

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  • ...It is known that enhancing strain hardening suppresses flow localization and, as a consequence, significantly improves stretchability of the sheet material [1, 2, 12, 42]....

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  • ...Hill [1], assuming a convex yield surface and the normality flow rule, predicts the conditions under which a velocity discontinuity occurs at zero and negative minor strain....

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