Abstract
Abstract The exact calculations of the stress and strain distributions based on the controlling equations for a forming process with large deformation are often difficult. To circumvent such difficulties, some analytical methods such upper-bound analysis and slip-line field theory have been established by making a number of simplifying assumptions regarding the material properties and deformation modes. In this work an analytical model based on the upper-bound theory was successfully developed to predict material flow pattern and maximum process loads for an Equal Channel Angular Pressing (ECAP) die with circular cross-section and an intersecting channel angle of 120°. Based on the model, the power dissipated on all frictional and velocity discontinuity surfaces were determined and optimized in order predict the maximum process force as function of the channel geometry and the material plastic behavior. To validate the developed model, the ECAP die were produced and used to determine experimental load-displacement curves of AA6061-T6 specimens with different lengths. A good correlation between theoretical and experimental results was observed. In addition, the constant friction factor demonstrated to have a strong effect on the relative extrusion pressure.
Highlights
Over the past decades, producing bulk ultrafine-grained (UFG) and nanostructured materials through the application of severe plastic deformation (SPD) methods has attracted a considerable interest in the field of materials science and engineering[1]
The results demonstrated that for constant friction factors close to zero the deformation zone occurs in a plane bounded by the intersection of two channels
The maximum theoretical extrusion force was in a good agreement with the experimental results, being the analytical model useful to correctly dimension the tooling and to determine the process variables for Equal Channel Angular Pressing (ECAP) different materials
Summary
Over the past decades, producing bulk ultrafine-grained (UFG) and nanostructured materials through the application of severe plastic deformation (SPD) methods has attracted a considerable interest in the field of materials science and engineering[1]. The most popular method of SPD is Equal Channel Angular Pressing/Extrusion (ECAP/ECAE), an innovative process capable of producing relatively uniform intensive plastic deformation in a variety of material systems, without causing substantial change in geometric shape or cross section[2]. During ECAP processing, a sample with square or round cross-section is pressed into a die with two intersecting channels of equal cross-section area. As the sample is pressed using a plunger, it shears at the intersection and exits through the second channel. As the cross-section is symmetric, the sample can be rotated before reentry into the die. Critical ECAP process variables include the die angle, temperature, number of passes through the die, and whether or not the specimen is rotated between passes[6,7]
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