Abstract
This thesis aims to accurately describe the plastic anisotropy of aluminium alloys
through a hierarchical multi-level method. Robust and efficient integration schemes
have been proposed for the explicit numerical integration of rate-dependent crystal
plasticity models.
On the mesoscale, the plastic anisotropy is modelled by crystal plasticity models
considering a representative volume element (RVE). The RVE consists of a number of
single grains and inherits the microstructural information of the polycrystalline material,
e.g. crystallographic texture, grain size and shape and grain boundary misorientation.
Five crystal plasticity models have been used in this work, namely the full-constraint
(FC) Taylor model, the Alamel model, the Alamel model with so-called type III
relaxation (Alamel Type III), the visco-plastic self-consistent (VPSC) model and the
crystal plasticity finite element method (CPFEM). The accuracy and applicability of
these crystal plasticity models when predicting the plasticity anisotropy have been
investigated for three different aluminium alloys. On the continuum scale, the yield
surface of the material is represented by advanced yield functions. Two yield functions
have been employed and investigated for this purpose, namely the Yld2004-18p yield
function and the Facet yield function. The yield function is a key component of an
anisotropic model in a finite element method (FEM) code, in addition to the flow rule
and work hardening law, for simulating plastic deformations. Advanced yield functions,
like Yld2004-18p, are conventionally identified by experiments, e.g. uniaxial tensile
tests, biaxial tension/compression tests and shear tests. However, the number of
available experimental tests is limited for sheet metals and most of the stress space is
not covered by the experiments. The multi-level modelling was made through
identifying the parameters of the advanced yield functions partially or fully by stress
points at yielding provided by crystal plasticity calculations. The accuracy and
applicability of this multi-level modelling scheme were evaluated for describing the
plastic anisotropy of three aluminium alloy sheets in this thesis.
through a hierarchical multi-level method. Robust and efficient integration schemes
have been proposed for the explicit numerical integration of rate-dependent crystal
plasticity models.
On the mesoscale, the plastic anisotropy is modelled by crystal plasticity models
considering a representative volume element (RVE). The RVE consists of a number of
single grains and inherits the microstructural information of the polycrystalline material,
e.g. crystallographic texture, grain size and shape and grain boundary misorientation.
Five crystal plasticity models have been used in this work, namely the full-constraint
(FC) Taylor model, the Alamel model, the Alamel model with so-called type III
relaxation (Alamel Type III), the visco-plastic self-consistent (VPSC) model and the
crystal plasticity finite element method (CPFEM). The accuracy and applicability of
these crystal plasticity models when predicting the plasticity anisotropy have been
investigated for three different aluminium alloys. On the continuum scale, the yield
surface of the material is represented by advanced yield functions. Two yield functions
have been employed and investigated for this purpose, namely the Yld2004-18p yield
function and the Facet yield function. The yield function is a key component of an
anisotropic model in a finite element method (FEM) code, in addition to the flow rule
and work hardening law, for simulating plastic deformations. Advanced yield functions,
like Yld2004-18p, are conventionally identified by experiments, e.g. uniaxial tensile
tests, biaxial tension/compression tests and shear tests. However, the number of
available experimental tests is limited for sheet metals and most of the stress space is
not covered by the experiments. The multi-level modelling was made through
identifying the parameters of the advanced yield functions partially or fully by stress
points at yielding provided by crystal plasticity calculations. The accuracy and
applicability of this multi-level modelling scheme were evaluated for describing the
plastic anisotropy of three aluminium alloy sheets in this thesis.
