Some aspects of Portevin–Le Chatelier plastic instabilities investigated by infrared pyrometry

Ranc, Nicolas; Wagner, Danièle

doi:10.1016/j.msea.2004.11.042

Cited by 71 publications

(45 citation statements)

References 25 publications

(30 reference statements)

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“…This phenomenon may be identical to instabilities encountered in the literature [21,22]. For the phenomenon of ageing dynamics, this inversion of the sensitivity of the stress as a function of temperature can be observed.…”

Section: Microstructural Changessupporting

confidence: 81%

An experimental investigation of the behaviour of steels over large temperature and strain rate ranges

Hor

Morel

Lebrun

et al. 2013

International Journal of Mechanical Sciences

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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. During forging and machining manufacturing processes, the material is subject to large strains at high strain rates which provoke local heating and microstructural changes. Modelling of these phenomena requires precise knowledge of the stress-strain constitutive equations for a large range of strains, strain rates and temperatures. An experimental study of the rheology of both hyper-and hypo-eutectoid steels (with different microstructures) over a temperature range from 20 1C to 1000 1C and with strain rates from 10 À2 to 10 5 s À1 has been undertaken. These tests were performed in compression on cylindrical specimens and in shear using hat-shaped specimens. Both a GLEEBLE 3500 thermomechanical testing machine and a Split-Hopkinson Pressure Bar apparatus were used. From these tests, three deformation domains have been identified as a function of the material behaviour and of the changes in the deformed microstructure. Each domain was characterized by its behaviour, including the competition between hardening and softening, strain rate sensitivity on the flow stress and the softening phenomenon (i.e. recrystallisation or recovery, etc.). Finally, based on thermodynamical considerations, the conditions of thermoplastic instability (i.e. shear bands, twinning, heterogeneities, etc.) and microstructural changes are highlighted using process maps of the dissipated power repartition.

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Section: Microstructural Changessupporting

confidence: 81%

An experimental investigation of the behaviour of steels over large temperature and strain rate ranges

Hor

Morel

Lebrun

et al. 2013

International Journal of Mechanical Sciences

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“…At low strain rates, uncorrelated static type-C bands are seen. The corresponding stress-time plot displays large amplitude nearly regular serrations as in experiments [28,29,[42][43][44][45][46].…”

Section: The Portevin-le Chatelier Bands In the Ananthakrishna Modelsupporting

confidence: 51%

General framework for acoustic emission during plastic deformation

2015

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Despite the long history, so far there is no general theoretical framework for calculating the acoustic emission spectrum accompanying any plastic deformation. We set up a discrete wave equation with plastic strain rate as a source term and include the Rayleigh-dissipation function to represent dissipation accompanying acoustic emission. We devise a method of bridging the widely separated time scales of plastic deformation and elastic degrees of freedom. While this equation is applicable to any type of plastic deformation, it should be supplemented by evolution equations for the dislocation microstructure for calculating the plastic strain rate. The efficacy of the framework is illustrated by considering three distinct cases of plastic deformation. The first one is the acoustic emission during a typical continuous yield exhibiting a smooth stress-strain curve. We first construct an appropriate set of evolution equations for two types of dislocation densities and then show that the shape of the model stress-strain curve and accompanying acoustic emission spectrum match very well with experimental results. The second and the third are the more complex cases of the Portevin-Le Chatelier bands and the Lüders band. These two cases are dealt with in the context of the Ananthakrishna model since the model predicts the three types of the Portevin-Le Chatelier bands and also Lüders-like bands. Our results show that for the type-C bands where the serration amplitude is large, the acoustic emission spectrum consist of well separated bursts of acoustic emission. At higher strain rates of hopping type-B bands, the burst type acoustic emission spectrum tends to overlap forming a nearly continuous background with some sharp acoustic emission bursts. The latter can be identified with the nucleation of new bands. The acoustic emission spectrum associated with the continuously propagating type-A band is continuous. These predictions are consistent with experimental results. More importantly, our study shows that the low amplitude continuous acoustic emission spectrum seen in both the type-B and A band regimes is directly correlated to small amplitude serrations induced by propagating bands. The acoustic emission spectrum of the Lüders-like band matches with recent experiments as well. In all of these cases, acoustic emission signals are burst-like reflecting the intermittent character of dislocation mediated plastic flow.

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“…Ranc and Wagner [92] and Louche and Chrysochoos [93] demonstrated this capability of thermographic methods by clearly distinguishing hopping type B bands from propagating type A bands. Using temperature field measurements, Ait-Amokhtar et al found a difference between type A and type B bands that has not been possible to detect by other means.…”

Section: Thermographic Techniquesmentioning

confidence: 95%

“…A typical thermal map of a propagating type A PLC band is shown in figure 15. To visualize the formation of PLC bands and accurately determine the band velocities, the thermal camera may be coupled with a pyrometer in an infrared pyrometry system such as that used by Ranc and Wagner [92]. Generally, the specimen surface is coated with a thin layer of black dye to homogenize the surface emissivity [40].…”

Section: Thermographic Techniquesmentioning

confidence: 99%

“…Ranc and Wagner studied an Al-Cu alloy at a constant strain rate and temperature and found that several type B bands can nucleate in the effective gauge of a specimen with a certain time interval between consecutive nucleations. The average interval was 95 ms, and band formation occurred within 1.5 ms of a stress drop [92]. Note that the time between successive serrations varies in proportion to the reciprocal strain rate, provided the plastic events take place under similar strains.…”

Section: Thermographic Techniquesmentioning

confidence: 99%

See 1 more Smart Citation

The Portevin–Le Chatelier effect: a review of experimental findings

Yılmaz¹

2011

Science and Technology of Advanced Materials

232

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The Portevin-Le Chatelier (PLC) effect manifests itself as an unstable plastic flow during tensile tests of some dilute alloys under certain regimes of strain rate and temperature. The plastic strain becomes localized in the form of bands which move along a specimen gauge in various ways as the PLC effect occurs. Because the localization of strain causes degradation of the inherent structural properties and surface quality of materials, understanding the effect is crucial for the effective use of alloys. The characteristic behaviors of localized strain bands and techniques commonly used to study the PLC effect are summarized in this review. A brief overview of experimental findings, the effect of material properties and test parameters on the PLC effect, and some discussion on the mechanisms of the effect are included. Tests for predicting the early failure of structural materials due to embrittlement induced by the PLC effect are also discussed.

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Some aspects of Portevin–Le Chatelier plastic instabilities investigated by infrared pyrometry

Cited by 71 publications

References 25 publications

An experimental investigation of the behaviour of steels over large temperature and strain rate ranges

An experimental investigation of the behaviour of steels over large temperature and strain rate ranges

General framework for acoustic emission during plastic deformation

The Portevin–Le Chatelier effect: a review of experimental findings

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