Formation de la striction dans la déformation à chaud par traction

Rossard, C.

doi:10.1051/metal/196663030225

Cited by 46 publications

(14 citation statements)

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“…ε m [157] and σ = K . ε m ε n [163] are regarded as constant but they should vary with the microstructural change, so they cannot precisely represent the superplastic behavior. Song et al [164] proposed an equation with varying m and n based on Backofen equation for superplastic flow.…”

Section: Constitutive Equations Of Superplasticitymentioning

confidence: 99%

“…It is used in the simple stress state without any strain effects Backofen et al[157] σ = K . ε m ε n It involves the combined effect of the strain rate sensitivity (m) and the strain hardening (n) Rossard et al[163] It describes the superplasticity in matrix composite (for aluminum matrix composite with Si 3 N 4 whiskers (20%), n = p = 2)Mabuchi and Higashi[166] σ = C . ε m + k o + R 1 − ξ 0.5Evaluates the deformation and internal damage of AA5083 alloy Khaleel et al[167] σ = k exp c o ln ε + for Al-Zn-Mg-Zr alloy Guan et al[168] …”

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confidence: 99%

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Recent Development of Superplasticity in Aluminum Alloys: A Review

Bhatta

Pesin

Zhilyaev

et al. 2020

Metals

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Aluminum alloys can be used in the fabrication of intricate geometry and curved parts for a wide range of uses in aerospace and automotive sectors, where high stiffness and low weight are necessitated. This paper outlines a review of various research investigations on the superplastic behavior of aluminum alloys that have taken place mainly over the past two decades. The influencing factors on aluminum alloys superplasticity, such as initial grain size, deformation temperature, strain rate, microstructure refinement techniques, and addition of trace elements in aluminum alloys, are analyzed here. Since grain boundary sliding is one of the dominant features of aluminum alloys superplasticity, its deformation mechanism and the corresponding value of activation energy are included as a part of discussion. Dislocation motion, diffusion in grains, and near-grain boundary regions being major features of superplasticity, are discussed as important issues. Moreover, the paper also discusses the corresponding values of grain size exponent, stress exponent, solute drag creep and power law creep. Constitutive equations, which are essential for commercial applications and play a vital role in predicting and analyzing the superplastic behavior, are also reviewed here.

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Section: Constitutive Equations Of Superplasticitymentioning

confidence: 99%

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confidence: 99%

Recent Development of Superplasticity in Aluminum Alloys: A Review

Bhatta

Pesin

Zhilyaev

et al. 2020

Metals

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“…(1) (where t is the strain rate and (Y is a constant) is unstable with respect to tension if n 2 3 (Rossard 1966;Hart, Campbell 1967); the rate at which the instability grows increases with the stress exponent n.…”

Section: Stability Of Continental Lithosphere Extensionmentioning

confidence: 99%

Rheological modelling and deformation instability of lithosphere under extension

Bassi

Bonnin

1988

Geophysical Journal International

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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 apriori 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.

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“…Theoretical analyses and laboratory experiments predict that the more non-linear, the more unstable materials will be in a tensile test (e.g. Rossard 1966: Campbell 1967. In other words, plastic materials are more prone to neck in the presence of a defect than are power-law materials with a low stress exponent.…”

Section: Introductionmentioning

confidence: 99%

Relative importance of strain rate and rheology for the mode of continental extension

Bassi

1995

Geophysical Journal International

121

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S U M M A R YBoth extension rate and rheology have been shown to influence the style of continental rifting. So far, their effect on the dynamics of extension has been discussed separately in the literature, leading to diverging conclusions. The rate of extension mostly affects the dynamics of rifting through the occurrence of syn-rift cooling at low extension rates. This cooling results in an increase of strength if the lithosphere has a temperature-dependent rheology. England (1983) first suggested that this effect will limit the amount of extension that an area may undergo. Kusznir & Park (1987) argued more generally that it will induce a widening of the rift, and concluded that extension rate is the major control on wide versus narrow rifting. Later studies (Bassi 1991; Bassi, Keen & Potter 1993). however, have demonstrated the importance of rheological layering within the lithosphere for the mode of continental extension by showing that a plasticity-dominated rheology will lead to rapid and narrow necking while a creep-dominated rheology results in wider rifts and margins. Gravitational stresses arising from density anomalies due to lithosphere thinning also affect the style of rifting (Buck 1991). In this paper, we examine the combined effect of these different parameters in order to reconcile earlier studies and assess the importance of syn-rift cooling for the process of lithospheric necking. The approach, introduced in a previous study (Bassi 1991), uses a finite-element technique to simulate extension of a vertical cross-section of the lithosphere. The effect of cooling on the necking pattern depends strongly on the rheology of the thinned lithosphere when it starts to cool. If heat diffusion always induces strengthening and delays rupture in time, it only modifies significantly the geometry of the rift when the upper mantle is weak and viscous. In this case, the locus of maximum strain rate migrates laterally once the central area starts to cool and harden, as hypothesized by Kusznir & Park (1987); eventually, strain concentrates at the transition between deformed and undeformed lithosphere. We predict that this pattern will induce asymmetric breakup and produce a very narrow margin and a wide, uniformly thinned, conjugate margin. In all other cases, i.e. when the upper mantle is initially in the low-plasticity regime, or if it reaches the yield stress during extension, the rate of extension appears to have little effect on the rifting pattern.

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Formation de la striction dans la déformation à chaud par traction

Cited by 46 publications

References 0 publications

Recent Development of Superplasticity in Aluminum Alloys: A Review

Recent Development of Superplasticity in Aluminum Alloys: A Review

Rheological modelling and deformation instability of lithosphere under extension

Relative importance of strain rate and rheology for the mode of continental extension

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