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ReseaRch PRogRammes
As they represent in an average sense the microstructural
rearrangements of the material, constitutive models describe
the stress and internal variables as functions of the strain,
strain rate and temperature. In large-scale simulations of
structures, the framework of continuum thermo-mechanics
is typically adopted to formulate the constitutive models,
while thermo-mechanical testing is used to identify the model
parameters. Advanced constitutive models, including plastic
anisotropy, non-linear isotropic and kinematic hardening,
strain-rate and temperature dependence, damage evolution
and failure, tend to have a large number of model parameters.
In close collaboration with the Lower Scale Programme, this
research programme applies multiscale methods to develop
validated constitutive models for large-scale simulations
of metal structures. Thus, the need for calibration of the
constitutive models against thermo-mechanical tests is
reduced and the prediction accuracy of the models is increased
with respect to properties that are not always easily measured
by testing. Qualitative and quantitative descriptions at different
length scales are closely accompanied by well-designed
experiments at the relevant length scales for the phenomena
of interest (from the nanoscale to the complete structure). This
provides a basis for achieving improved understanding, model
development and model validation. As the quantum, atomistic
and nanoscales are covered by the Lower Scale Programme,
this programme deals with crystal plasticity and continuum
plasticity at the micro-, meso- and macroscales.
The main themes in the research activities in 2016 have been:
• Micromechanical modelling of ductile fracture in aluminium
alloys (PhD, Lars Edvard Bryhni Dæhli)
• Ductile fracture of aluminium alloys at low stress triaxiality:
an experimental and numerical study (PhD, Bjørn Håkon
Frodal)
• Micromechanical modelling and simulation of steel
materials (PhD, Sondre Bergo)
• Modelling and simulation of localization, damage and
fracture in age-hardening aluminium alloys (Principal
investigator S. Dumoulin)
• Micromechanical modelling and simulation of dual-phase
steels (Principal investigator A. Saai)
• Strain gradient plasticity (Principal investigator T. Berstad)
In addition to researchers at SINTEF Materials & Chemistry
and professors at NTNU, three PhD candidates are linked to
the activities in the research programme, namely Lars Edvard
Bryhni Dæhli (2013-2017), Bjørn Håkon Frodal (2015-2019) and
Sondre Bergo (2016-2020).
As an example of the research activities, the SIMLab Crystal
Mechanics Model (SCMM) has been extended in 2016 by
including dynamic strain aging, which leads to jerky plastic
flow in some aluminium alloys and inhomogeneous deformation
with propagating localization bands. We can now model this
behaviour using the crystal plasticity finite element method
where grains are discretized into elements. Figure 5 shows a
finite element model of a tensile test in which the grains are
discretized, while the simulated propagating localization bands
under tensile loading are illustrated in Figure 6.
Metallic Materials
Head of Programme: Odd Sture Hopperstad
Figure 5: Mesh of the 3D aggregate made of 1200 grains.
Figure 6: Contour plots of von Mises plastic strain rate (log scale) from the
simulation with initial rate of 1.0×10-
2
s-
1
.