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SHEAR BEHAVIOR AND RELATED MECHANISMS IN MATERIALS PLASTICITY

Plastic Behavior of Metals at Large Strains: Experimental Studies Involving Simple Shear

[+] Author and Article Information
E. F. Rauch

Grenoble INP, SIMaP/GPM2, CNRS-UJF, BP 46-38402, Saint Martin d’Hères Cedex, Franceedgar.rauch@simap.grenoble-inp.fr

Automated crystal orientation mapping with a TEM.

J. Eng. Mater. Technol 131(1), 011107 (Dec 22, 2008) (8 pages) doi:10.1115/1.3030942 History: Received February 19, 2008; Revised June 06, 2008; Published December 22, 2008

Two experimental devices that promote simple shear are used to investigate the plastic behavior of metals under very large strains. First, researches on the anisotropic behaviors of sheets of metals performed with the help of the planar simple shear test are reviewed. In particular, it is shown that, with this device, stage IV may be reached and analyzed on polycrystals as well as on single crystals. The second part is devoted to equal channel angular extrusion, which is known to promote grain refinement after several passes. A direct comparison of the crystallographic textures measured on sheared and on extruded samples confirms that the extrusion promotes massively simple shear. Besides, the grain refinement is measured with a dedicated transmission electron microscopy (TEM) attachment. It is shown that the grain size decreases regularly for a low carbon steel as well as for copper, down to around 1μm. It is argued that the sustained hardening in stage IV is a mechanical signature of the grain size decrease. The trend is interpreted and reproduced quantitatively with the help of a simple modeling approach.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Successive geometries adopted for planar simple shear tests. The calibrated part is delineated either by machining a groove (a) in the thickness (G’Sell (4)), (b) along the length (Miyauchi (5)) of the sample, or (c) by clamping the lateral parts with adequate tools (Rauch (24)).

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Figure 2

Sketch of the Fe–Si single crystal plate showing the orientation of the shear samples

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Figure 3

Experimental shear stress-shear strain curves for the Fe–2.9%Si single crystal sheared in the [111] and [112¯] directions

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Figure 4

Aspect of the unconstrained end of the sample for (a) moderate and (b) large shear strains illustrating the damage occurring at a large strain

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Figure 5

Cumulated shear stress-shear strain curves for a polycrystalline copper sample whose length is reduced between two tests in order to reduce the damage effect on the stress level

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Figure 6

Work-hardening rate versus resolved shear stress for a pure Al single crystal sheared along the [111] multiple slip direction

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Figure 7

Orientation of extruded and sheared samples in a AA5383 thick plate

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Figure 8

The (111) pole figures for AA5383 after (a) a simple shear up to γ=0.7 and (b) one extrusion that leads to γ=2. Note the similitude in the textural components for these two deformation modes.

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Figure 9

TEM characterization of an IF steel extruded eight times (route C) at 210°C, (a) orientation map, (b) bright field image, and (c) reliability map for the same area (300×300 pixels with a step size of 28 nm)

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Figure 10

Evolution of the measured grain size with strain for a copper polycrystal and a low carbon steel extruded at room temperature

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Figure 11

Work-hardening rate versus resolved shear stress curves deduced from the results shown in Fig. 5 on copper polycrystal (discontinuous curve) and calculated with the dislocation and grain size hardening model (continuous curve)

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Figure 12

Extrapolation of the theoretical curves for deformation at temperature lower (f=2.5) or higher (f>3.5) than room temperature. The case f=3.5 corresponds to the curve shown in Fig. 1.

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