Upper-bound sensitivity analysis of the ECAE process

In this work the theoretical solutions based upon the upper-bound theorem proposed recently by Pérez and Luri [Mech. Mater. 40 (2008) 617] for the equal channel angular extrusion process (ECAE) are employed with a proposed 25 central composite factorial analysis. The upper-bound solutions consider Tresca friction conditions and different fillet radii located at the die channels intersection. The uniaxial mechanical properties of commercial pure aluminium are used assuming isotropic nonlinear work-hardening wherein the strain-rate effects are accounted for by the ratio between the accumulated effective plastic strain and the time resulting from the ECAE deformation zones. Also, von Mises and Drucker isotropic yield criteria are adopted to predict the ECAE load. Bearing in mind that in the ECAE process the billet is under a simple shear stress state, a direct effect of the tooling frictional conditions is observed, namely, the increase in the ECAE load is promoted by severe friction conditions or increasing values of the ratio defined between the pure shear and uniaxial tension/compression yield stresses. From the proposed composite 25 factorial analysis, the main parameters affecting the ECAE pressure and/or load may be ranked as: (1) Tresca 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 outer and inner fillet radii.