Impact of distortional hardening and the strength differential effect on the prediction of large deformation behavior of the Ti6Al4V alloy

The ability of three plasticity models to
predict the mechanical behavior of Ti6Al4V until
fracture is presented. The first model is the orthotropic
yield criterion CPB06 developed by Cazacu et al. (Int J
Plast 22:1171–1194, 2006) with a distortional hardening,
allowing for the description of material
anisotropy and the strength differential effect. The
second model is the anisotropic Hill’48 yield criterion
with distortional hardening, describing the material
anisotropy with quadratic functions but is unable to
model the strength differential effect. Finally, the third
model is the classical Hill’48 yield locus with isotropic
hardening. Distortional hardening is modeled through
five yield surfaces associated with five levels of plastic
work. Each model is validated by comparing the finite
element predictions with experimental results, such as
the load and displacement field histories of specimens
subjected to different stress triaxiality values. Tensile
tests are performed on round bars with a V-notch, a
through-hole, and two different radial notches; compression
tests are performed on elliptical cross-section
samples. The numerical results show that none of the
models can perfectly predict both the measured load
and the sample shape used for validation. However,
the CPB06 yield criterion with distortional hardening
minimizes the global error of the model predictions.
The results provide a quantification of the influence of
mechanical features such as hardening phenomenon,
plastic anisotropy, and tension–compression asymmetry.
The impact of these features on the prediction of
the post-necking deformation behavior of the Ti6Al4V
alloy is explored.