Numerical Investigation of Plastic Strain Homogeneity during Equal-Channel Angular Pressing of a Cu-Zr Alloy

A three-dimensional finite element method (3D FEM) simulation was carried out using ABAQUS/Explicit software to simulate multi-pass processing by equal-channel angular pressing (ECAP) of a circular cross-sectional workpiece of a Cu-Zr alloy. The effective plastic strain distribution, the strain homogeneity and the occurrence of a steady-state zone in the workpiece were investigated during ECAP processing for up to eight passes. The simulation results show that a strain inhomogeneity was developed in ECAP after one pass due to the formation of a corner gap in the outer corner of the die. The calculations show that the average effective plastic strain and the degree of homogeneity both increase with the number of ECAP passes. Based on the coefficient of variance, a steady-state zone was identified in the middle section of the ECAP workpiece, and this was numerically evaluated as extending over a length of approximately 40 mm along the longitudinal axis for the Cu-Zr alloy.

Effect of ECAP on the Plastic Strain Homogeneity, Microstructural Evolution, Crystallographic Texture and Mechanical Properties of AA2xxx Aluminum Alloy

This study presents a comprehensive evaluation of Equal Channel Angular Pressing (ECAP) processing on the structural evolution and mechanical properties of AA2xxx aluminum alloy. Finite element analysis (FE) was used to study the deformation behavior of the AA2xxx billets during processing in addition investigate the strain homogeneity in the longitudinal and transverse direction. Billets of AA2011 aluminum alloy were processed successfully through ECAP up to 4-passes with rotating the sample 90° along its longitudinal axis in the same direction after each pass (route Bc) at 150 °C. The microstructural evolution and crystallographic texture were analyzed using the electron back-scatter diffraction (EBSD) and optical microscopy (OM). An evaluation of the hardness and tensile properties was presented and correlated with the EBSD findings and FE simulations. The FE analysis results were in good agreement with the experimental finding and microstructural evolution. Processing through 4-passes produced an ultrafine-grained structure (UFG) and a recrystallized fine grain dominated the structure coupled with a geometric grain subdivision which indicated by grain refining and very high density of substructures. This reduction in grain size was coupled with an enhancement in the hardness, tensile strength by 66.6%, and 52%, respectively compared to the as-annealed counterpart. Processing through 1-pass and 2-passes resulted in a strong texture with significant rotation for the texture components whereas 4-passes processing led to losing the symmetry of the texture with significant reduction in the texture intensity.

The Influence of ECAP Geometry on the Effective Strain Distribution

Equal channel angular pressing (ECAP) is one of the most well-known severe plastic deformation (SPD) method for formation the UFG (ultrafine-grained) structures. This method provides very high strains leading to the extreme work hardening and microstructural refinement. To increase the efficiency of ECAP method, there is necessary to design the geometry of ECAP die with focus on high degree of plastic deformation homogeneity. The present study deals with the influence of channel angle on the deformation behavior and strain homogeneity in the transverse direction of sample after two ECAP passes. This analysis was carried out through finite element simulations in the Deform program. In the simulation, three main factors such as an intersecting angle of Ф = 90°, 100°, 110° a 120°, outer corner angle R (ψ) and inner corner angle (r) were being varied. The equation describing the dependence of R and r on average value of the effective plastic strain for different channel angles was established. Moreover, strain inhomogeneity index (Ci) in the transverse direction of sample was also calculated. The results from simulations have indicated that if the outer corner angle increases, mean effective strain decreases. After two ECAP passes (route C), there was seen the increase in strain homogeneity of the sample's cross section.

Microdevice for Delivering Homogeneous Equi-Biaxial Strain to Live Cells Without the Use of Platen Structures

Live cells from most of the membranous tissues such as alveoli are subjected to equi-biaxial strain originated from their extracellular environments. To understand the role of equi-biaxial strain in live cells, a number of engineered methods have been developed for applying such mechanical strain to in vitro cultured cells. Among these methods, deforming a flexible substrate on a circular platen has been widely used [1], and has been miniaturized into millimeter scale for parallel stretching assay (Figure 1a). Nonetheless, the strain homogeneity becomes increasingly challenging at smaller scale, since it requires an ultra-thin membrane, an indentation platen with well controlled dimension, and the highly precise alignment. This obviously increases the fabrication and operation complexities. Devices that deliver homogeneous strain with minimal fabrication and assembling complexities are needed.