Strain-path change induced transients in flow stress, work hardening and r-values in aluminum

Abstract

Commercially pure aluminum with random texture was prestrained either by rolling or by uniaxial compression, and then tested in uniaxial tension to study the transients in flow stress, work hardening and r-value induced by the strain-path change. New experimental results are reported on the variation of the r-value and the permanently reduced work hardening subsequent to the strain-path change. A continuum plasticity model was developed that can reproduce the observed behavior. The model applies a second-order "delayed pointer" tensor to represent the microstructural anisotropy and was implemented into the finite element software LS-DYNA. The model was calibrated to the experimental data, and a simulation of early strain localization subsequent to an orthogonal strain-path change was compared to strain fields measured by a digital image correlation technique.2

Modeling strain-path changes in aluminum and steel

“…The HAH model (Barlat et al, 2014) is modified to capture SPC transients observed in aluminum, i.e., hardening stagnation after reverse SPCs and permanent softening after orthogonal SPCs. Predictions by the HAH model are compared to the MHH model (Mánik et al, 2015), which was originally developed for aluminum. The MHH model turned out to be directly applicable to an extra deep drawing quality (EDDQ) steel without any modifications.…”

“…These anisotropic hardening behaviors can, in general, be described by a yield surface that changes shape and size during plastic deformation. A recent review can be found in Mánik et al (2015).…”

“…Holmedal et al (2010) proposed a plasticity model which applied second-order tensors to keep track of the strain history. The model was further modified by Mánik et al (2015). In contradiction to the Teodosiu-Hu model, the permanent softening occurring after reverse or orthogonal loading is captured in this model.…”

“…However, in this paper, the HAH model is further developed to include both reverse and orthogonal SPC behavior and thus to describe the type of transients observed in aluminum. The modified HAH model is then compared with the MHH model using earlier published experimental data for aluminum and steel, i.e., the stress-strain curves subsequent to complex SPCs for commercially pure aluminum reported by Mánik et al (2015) and similar results presented by Ha et al (2013) for an extra deep drawing quality (EDDQ) steel.…”

“…The SPC experiments by Ha et al (2013) indicate that the EDDQ steel exhibits a strong cross-hardening effect during orthogonal loading. The commercially pure aluminum investigated by Mánik et al (2015) exhibits a strong and complex Bauschinger effect and also a strong cross-hardening effect. The EDDQ steel has earlier been modeled by the "extended" and "enhanced" (Barlat et al, 2014;Lee et al, 2015) HAH models, while commercially pure aluminum has been modeled by the MHH model.…”