Abstract
In this work the theoretical solutions based upon the upper-bound theorem recently proposed by Perez and Luri [Mech. Mater. 40 (2008) 617] for the equal channel angular extrusion process (ECAE) are analyzed by performing a 25 central composite factorial analysis. The uniaxial mechanical properties of commercial pure aluminium are considered by assuming isotropic nonlinear work-hardening combined to von Mises and Drucker isotropic yield criteria to predict the ECAE load and the effective plastic strain. From the proposed 25 factorial analysis, the main parameters affecting the ECAE pressure may be ranked as: (1) Friction factor, (2) die channels intersection angle, (3) outer and (4) inner die corners fillet radii and lastly, (5) plunger velocity. Alternatively, the effective plastic strain is mainly controlled by the die channels intersection angle and, in a less extent, by the outer and inner die corners fillet radii.
Highlights
The equal channel angular extrusion process (ECAE) is a severe plastic deformation process employed to produce bulk ultra-fine grained materials with improved mechanical properties [1, 2]
One can observe the existence of a direct effect from the frictional conditions, namely, the ECAE pressure increases significantly with the friction factor f or in a less extent with the yield stress ratio κ/σy
Analytical investigations based upon the upper-bound method, including the material strain-rate effects and two isotropic plasticity yield criteria are proposed in the present work in order to evaluate the extrusion pressure and the effective plastic strain associated to the processing of a commercial pure aluminium
Summary
The equal channel angular extrusion process (ECAE) is a severe plastic deformation process employed to produce bulk ultra-fine grained materials with improved mechanical properties [1, 2]. The consideration of material nonlinear work-hardening to predict the ECAE pressure, assuming a frictionless condition with an outer die corner radius, was firstly proposed by Alkorta and Sevillano [4] Their analytical solution is based upon the upper-bound theorem and provides a good agreement with numerical predictions determined from a plane-strain finite element model. Based upon the review presented here above, it is clear the need for more general modelling techniques to describe the effects of the relevant parameters on the strains and mechanical properties resulting from the ECAE, namely, tooling geometry, billet material, friction conditions and processing velocity Into this context, the present work firstly aims at providing a sensitivity analysis with the help of the 2K central composite factorial design to evaluate the influence of these parameters on the effective plastic strain and the extrusion pressure for commercial pure aluminum and some typical die configurations by means of the variance analysis
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