TESE DE DOUTORADO

Abstract

The ECAP technique is a severe plastic deformation process in which a billet is forced to flow under a simple shear condition through a die composed of identical channels that are intercepted at an angle Φ. The literature presents a great number of studies related to this technique. However, they are restricted to the exploration of results from specific set of parameters. In this context, the present work is destined to include work-hardening and strain-rate dependent materials in the upper-bound solutions proposed by Pérez and Luri to estimate the pressing force/pressure and the effective plastic strains. These solutions are associated to single pass of pressing at room temperature. At the same time, the finite element method was applied for the development of two-dimensional (2D) and threedimensional (3D) models that are able to provide accurate predictions of pressing force and effective plastic strains for either materials sensible or not to strain rate effects. Also, the numerical models proposed are related to single pressing at cold. Using the aluminium Al 6070 and Al 1100 alloys, the exploration and validation of the extended models was performed by comparison with experimental results of force. Besides, from the analysis of the 2D models, the evaluation of the plasticity condition allowed to verify that the material was plastically deformed when it crosses the channels intersection region. This fact was not explored in the recent literature. In addition, the limitation of the uniaxial tensile or compression hardening curves for the representation of this severe forming process is shown. Afterwards, the factorial 2 qualitative analysis permitted an appreciable classification in order of relevance was showed for all considered parameters in the proposed theoretical models. Moreover, this analysis indicated the die configurations and pressing conditions that should be intensively investigated. The simulation of these cases, considering a hypothetical material with plastic or viscoplastic behaviors, revealed that the strain-rate effect increases the load predictions. This fact was confirmed by the curves of von Mises effective stresses. In addition, shearing is the predominating deformation mode in the absence of fillet radii and only with the outer fillet radii. For dies with identical fillet radii, the material was deformed by shearing and bending. On the other hand, using interstitial free steel, the existence of critical friction condition that avoids the adherence phenomenon and the heterogeneous effective plastic strain distributions were verified. Finally, the consistency of the 2D and 3D numerical models in the simulation of the equal channel angular pressing was investigated in terms of load, by the comparison with the experimental predictions for aluminum Al 1100 alloy.