Abstract
Equal-Channel Angular Pressing (ECAP) is a method used to introduce severe plastic deformation into a metallic billet without changing its geometry. In special cases, strain localization occurs and a pattern consisting of regions with high and low deformation (so-called shear and matrix bands) can emerge. This paper studies this phenomenon numerically adopting two-dimensional finite element simulations of one ECAP pass. The mechanical behavior of aluminum is modeled using phenomenological plasticity theory with isotropic or kinematic hardening. The effects of the two different strain hardening types are investigated numerically by systematic parameter studies: while isotropic hardening only causes minor fluctuations in the plastic strain fields, a material with high initial hardening rate and sufficient strain hardening capacity can exhibit pronounced localized deformation after ECAP. The corresponding finite element simulation results show a regular pattern of shear and matrix bands. This result is confirmed experimentally by ECAP-processing of AA6060 material in a severely cold worked condition, where microstructural analysis also reveals the formation of shear and matrix bands. Excellent agreement is found between the experimental and numerical results in terms of shear and matrix band width and length scale. The simulations provide additional insights regarding the evolution of the strain and stress states in shear and matrix bands.
Highlights
Equal-Channel Angular Pressing (ECAP) is a severe plastic deformation (SPD) process developed by Segal [1,2]
Strain localization is observed in experiments if the strain hardening capacity (SHC) of the material subjected to ECAP is low
Kinematic hardening with high initial hardening rate and sufficient strain hardening capacity can lead to pronounced localized deformation in form of shear and matrix bands
Summary
Equal-Channel Angular Pressing (ECAP) is a severe plastic deformation (SPD) process developed by Segal [1,2]. In addition to experimental investigations, finite element (FE) simulations have been carried out to understand the ECAP process in greater detail For this purpose, multiple parameter studies were conducted, e.g., studying the effect of variations of the channel angle Φ [16,17,18,19], the angle of the outer curvature Ψ [18,19,20,21,22,23], the strain rate [24,25,26] as well as the friction between the channel and the billet [16,18,23,26,27]. The origin of the heterogeneous plastic flow is discussed both from a microstructural and a mechanical point of view, representing a starting point for further basic research on localization phenomena during SPD processing
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