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Research Papers

Principles of Nonequal Channel Angular Pressing

[+] Author and Article Information
Arman Hasani, László S. Tóth, Benoît Beausir

Laboratoire de Physique et Mécanique des Matériaux, Université Paul Verlaine de Metz, Ile du Saulcy, 57045 Metz, France

J. Eng. Mater. Technol 132(3), 031001 (Jun 15, 2010) (9 pages) doi:10.1115/1.4001261 History: Received January 27, 2009; Revised February 01, 2010; Published June 15, 2010; Online June 15, 2010

Abstract

A variant of the equal channel angular pressing (ECAP) process is examined in this paper where the channels are of rectangular shape with different thicknesses while the widths of the channels are the same. The process is named nonequal channel angular pressing and it is similar to the earlier introduced dissimilar channel angular pressing (DCAP) process. In DCAP, however, the diameters are near values, with the exit channel being slightly larger, while in NECAP, the exit channel is much smaller attributing several advantages to nonequal channel angular pressing (NECAP) with respect to ECAP. In this work an analysis is performed to determine the strain mode in a 90 deg NECAP die. A new flow line function is also presented to better describe the deformation field. The proposed flow line function is validated using finite element simulations. A comparison is made between ECAP and NECAP. Finally, texture predictions are presented for NECAP of fcc polycrystals. The advantages of this severe plastic deformation process are the following: (i) significantly larger strains can be obtained in one pass with respect to the classical ECAP process, (ii) grains become more elongated that enhances their fragmentation, and (iii) large hydrostatic stresses develop that improve the stability of the deformation process for difficult-to-work materials. The results obtained concerning the deformation field are also applicable in the machining process for the plastic strains that imparted into the chips.

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Figures

Figure 1

Ideal geometry of the NECAP process

Figure 2

Geometrical parameters for the flow line description of NECAP

Figure 3

Variations of the nonzero components of the velocity gradient as a function of the angular position along the flow line for p/c=2 in a 90 deg die. (a) Comparison for two values of the n parameter. (b) Comparison between ECAP and NECAP for n=6.

Figure 4

Dependence of the accumulated equivalent von Mises strain on the n parameter for ECAP–90 deg (p/c=1) and NECAP-90 deg (p/c=2) in one pass

Figure 6

{111} pole figures showing the textures after one pass in ECAP and in NECAP (p/c=2). The dotted lines indicate the ideal shear plane and SPN is the shear plane normal. Isovalues: 0.8, 1, 1.3, 1.6, 2, 2.5, 3.2, 4, 5, and 6.4.

Figure 7

Flow lines obtained from finite element analysis (identified by circles) and fitted by the proposed flow line function (continuous lines) in NECAP (p/c=2). The broken lines indicate the extent of the strain zone, where +1% means 1% of the total strain and −1% is 99% of the total strain in one pass.

Figure 8

The n parameter of the flow line and the accumulated von Mises strain in one pass as a function of its entering position x0 within the NECAP die as it is obtained from fitting of the FE-obtained trajectories.

Figure 5

The ideal orientations of simple shear and ECAP deformations as well as the textures that develop in one pass shown in two sections of the ODF. For NECAP, p/c=2. Isovalues in the ODFs: 0.7, 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, and 16.

Figure 9

Variation of the von Mises equivalent strain rate along the flow lines as a function of the angular position (obtained from the flow line approach). The punch velocity is 10 mm/min, and the die thickness is p/c=10 mm/5 mm

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