Project partners:
Most materials exhibit rate-dependent inelastic behaviour.
Increasing strain-rate usually increases the yield stress thus
enlarging the elastic range.
However, the ductility is gradually lost and for some materials
there exist a rather sharp transition strain-rate after which the material
behaviour is completely brittle, see the figure below.
The red curve correponds to a case where the strain rate is above the
transition value resulting in a brittle behaviour, whereas the blue curve
corresponds to a slow loading thus showing ductile behaviour.
In this project a phenomenological model for the ductile to brittle transition of rate-dependent solids will be developed. The model is based on consistent thermodynamic formulation using proper expressions for the Helmholtz free energy and the dissipation potential. In the model the dissipation potential is additively split into damage and visco-plastic parts and the transition behaviour is obtained using a stress dependent damage potential. Two video clips from the simulation of a compression test with high strain rate, resulting in a brittle failure. Coarse 12x6 mesh trilinear element (B-bar) mesh. Plane strain condition imposed.
For simulations of brittle failure see the following animations by Kari Kolari.
A coupled magnetoelastic constitutive model for isotropic
ferromagnetic materials is being developed.
The model is written on the basis of the Helmholtz free energy in which the
strain tensor and the magnetic induction vector are chosen as the basic variables.
For initially isotropic magnetoelastic solids the Helmholtz free energy depends
on five invariants
which form the integrity basis of an isotropic tensor function
depending on a symmetric second order tensor and a vector.
In the figure the magnetostrictive strain is shown as a function of the magnetic induction.
The solid line represents the prediction of the model and the line with markers
is experimentally observed magnetostriction in a stress free rod.
