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Necking

About: Necking is a research topic. Over the lifetime, 5280 publications have been published within this topic receiving 113945 citations.


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Journal ArticleDOI
TL;DR: In this paper, the authors examined the evolution of lateral inhomogeneities in the lithosphere, represented by small-scale variations of thickness, and concluded that no unstable behavior of the upper crust is observed unless the latter is more dense than the asthenosphere, in which case a gravitational instability may develop.
Abstract: SUMMARY Continental break-up, which precedes oceanic accretion, probably results from an unstable extension of the lithosphere, analogous to necking of metals when they are submitted to tension. By reason of complexity of the rheology, no conclusion about lithospheric extension stability may be reached by an a priori analysis. We thus examine directly the evolution, when the lithosphere is stretched, of lateral inhomogeneities, represented in our example by small-scale variations of thickness. The rheological model is derived from the hypotheses of Brace & Kohlstedt (1980) and is consistent with the results of rock mechanics. The lithosphere consists of three or four layers of varying thicknesses and mechanical properties. The brittle upper crust and, eventually, the brittle part of the mantle are assimilated to perfectly plastic media and are described, in a state of uniform extension, by a constant viscosity. In the lower crust and ductile mantle lithosphere, the effective viscosity is supposed to be exponential. The mechanical model relies on a perturbation method developed, by Fletcher & Hallet (1983), among others. Contrary to previous published results, no unstable behaviour of the lithosphere is observed unless the latter is more dense than the asthenosphere, in which case a gravitational instability may develop. This discrepancy can be explained by differences in assumptions concerning the variation of strength in the lithosphere, as yet poorly constrained by the data. We observe a great sensitivity of the results to the strength stratification and to the artificial discontinuities of density or viscosity implied by the models.

46 citations

Journal ArticleDOI
TL;DR: In this paper, a procedure is presented to identify the post-necking work hardening behavior of thick HSS steels using a standard uniaxial tensile machine, which is extended beyond necking by performing an inverse identification using the Finite Element Model Update technique and the heterogeneously.

46 citations

Journal Article
TL;DR: In this article, conditions sufficient for instability of deformation are examined for a class of incrementally non-linear, time independent inelastic solids, and the conditions are extended to deformation paths under generał assumptions which ensure that the incrementa) boundary value problem can be given a variational formulation.
Abstract: CONDITIONS sufficient for instability of deformation are examined for a class of incrementally non­ linear, time independent inelastic solids. Instability of a quasi-static deformation process (path) at varying loading is distinguished from a narrower concept of an unstable equilibrium state. The en­ ergy criterion is extended to deformation paths under generał assumptions which ensure that the incrementa) boundary value problem can be given a variational formulation. For a discretized prob­ lem, fulfilłment of the instability condition along a path is shown to imply either instability of the traversed equilibrium states in a dynamie sense or persisting possibility of quasi-static bifurcation at varying loading. For a continuum, instability at varying loading is interpreted as sensitivity of the incremental deformation to arbitrarily small perturbmg forces.

45 citations

Journal ArticleDOI
01 Sep 2017
TL;DR: In this article, an inverted VDA test frame was developed to incorporate digital image correlation (DIC) strain measurement during the bend test and a variety of advanced high strength sheet materials were evaluated.
Abstract: The VDA238-100 standard for tight radius bending (v-bending) of sheet materials has received widespread acceptance with automotive suppliers and material producers to characterize local formability However, the test fixture and tooling in the v-bend test standard is not amenable to direct strain measurement and the operator cannot terminate the test at the onset of crack initiation as the outer bend surface is not visible Consequently, fracture is identified using a load threshold and the bend angle estimated from an analytical formula based upon the punch displacement and tooling geometry Bend angles are not directly transferable and must be interpreted relative to the sheet thickness and bend radius unlike a strain measurement By obtaining an in-situ strain measurement on the surface using digital image correlation (DIC), the plane strain fracture limit can be accurately identified at the onset of cracking and remove ambiguity in translating the bend angles to practical forming operations and simulations A novel inverted VDA test frame was developed to incorporate DIC strain measurement during the bend test and a variety of advanced high strength sheet materials were evaluated It was observed that the VDA bend test creates a homogeneous strain state of plane strain across the width of the sample along with a proportional strain path to fracture without necking that is ideal for fracture characterization A correlation is developed to relate the bend angle with the major strain for the materials considered and accounts for the sheet thickness and bend radius A comparison of the bend angle obtained using the formula in the VDA standard based on the punch displacement was in very good agreement with manual measurements and an algorithm to measure the bend angle using DIC analysis was developed

45 citations

Journal ArticleDOI
TL;DR: In this paper, the authors evaluated the formability of multilayer metallic sheets by tensile, V-bending, hat bending and hemming tests, and found that a monolithic type-420J2 stainless steel sheet cannot be formed because of poor elongation as small as 1.7%.

45 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023174
2022351
2021241
2020249
2019213
2018238