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An analysis by the finite element method of material deformation in equal channel angular extrusion /

Deformation behavior of the work piece during equal channel

Bibliographic Details
Main Author: Yun, Su-jin
Format: Thesis Book
Language:English
Published: [Place of publication not identified] : [publisher not identified] ; 1996.
Subjects:
Major mechanical engineering.
Online Access:http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=743267701&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD
Description
Summary:Deformation behavior of the work piece during equal channel
angular extrusion (ECAE) processing is predicted using the
commercial finite element code ABAQUS. ECAE has a number of
advantages over conventional extrusion processes including
nearly homogeneous deformation, the ability to develop a
variety of microstructures and the ability to repeat the
process without changing work piece cross-section and
dimensions. Equal channel angular extrusion is a unique
process which results in shear deformation via simple shear
with a uniaxial compressive stress superimposed. Initially,
slip line theory formed the theory of ECAE and was limited to
an ideal rigid plastic material model. However, proper
design of the die requires the knowledge of the influence of
variables such as friction conditions, realistic material
models, and work piece geometry on the process mechanics. In
order to obtain more realistic estimation of the stress and
strain distribution throughout the work piece, it is
necessary to analyze ECAE using an elastic-plastic model.
This is accomplished herein using finite element models which
are based on the principle of virtual work rate and include
finite deformation. Deformation of the work piece and punch
pressure are strongly dependent on the number of elements
used and die angle. The smoothness given at the die
junctions (corner where shear plane begins) significantly
affects the distribution of plastic strain as well as
deformation of the work piece. The development of a gap or
clearance between the work piece and the die is also a
function of element size and die junction smoothness.
Distortion of the work piece due to a limited length for the
extrusion channel is due to the rigid body rotation and
strongly depends on the material, the number of elements and
the time increment for calculations. The elastic-plastic
analysis yields more reliable results in the elastic
deformation region than the rigid plastic analysis. The
numerical results for the perfectly plastic analysis with a
die angle of 90' shows good agreement with the theory of ECAE
for punch pressure and the shear plane angle. However, the
perfectly plastic analysis for a die angle greater than 90'
shows a deviation from ECAE theory as well as the development
of a free surface near the junction of the die. Moreover, a
free surface is developed for work hardening materials
regardless of die angle.
Item Description:Vita.
"Major Subject: Mechanical Engineering".
Physical Description:xvi, 155 leaves : illustrations ; 28 cm.
Issued also on microfiche from University Microfilms Inc.
Bibliography:Includes bibliographical references.