Engineering Fracture
Mechanics 75 (2008), 1921-1943.
EVALUATION OF DIRECTIONAL MESH BIAS IN CONCRETE FRACTURE
SIMULATIONS USING CONTINUUM DAMAGE MODELS
Milan
Jirásek
Czech Technical University in
Prague,
Czech Republic
and
Peter
Grassl
University of Glasgow, Scotland
Abstract
In the present comparative study, we investigate the influence of
directional mesh bias on the results of failure simulations performed
with isotropic and anisotropic damage models. Several fracture tests
leading to curved crack trajectories are simulated on different meshes.
The isotropic damage model with a realistic biaxial strength envelope
for concrete is highly sensitive to the mesh orientation, even for fine
meshes. The sensitivity is reduced if the definition of the
damage-driving variable (equivalent strain) is based on the modified
von Mises criterion, but the corresponding biaxial strength envelope is
not realistic for concrete. The anisotropic damage models used in this
study capture reasonably well arbitrary crack trajectories even if
the biaxial strength envelope remains close to typical
experimental data. Their superior performance can be at least partially
attributed to their ability to capture dilatancy under shear, which is
revealed by a comparative analysis of the behavior of individual models
under shear with restricted or free volume expansion.
Conclusions
The evaluation of mesh-induced directional bias of two isotropic and
two anisotropic damage models on different types of meshes for a number
of concrete fracture tests has lead to the following conclusions:
- The isotropic damage model with a realistic biaxial
strength envelope is strongly sensitive to the mesh orientation,
even if the mesh is fine.
- The isotropic damage model with a modified von Mises definition
of equivalent strain appears to be less sensitive to the mesh
orientation, but this is to a large extent an artifact caused by the
unrealistic increase of tensile strength under compression parallel to
the crack.
- The rotating crack model with transition to scalar damage leads
in general to better results than the isotropic model with a similar
type of biaxial strength envelope.
- The microplane-based anisotropic damage model can capture
arbitrary crack trajectories reasonably well, and its biaxial
strength envelope is close to typical experimental data for
concrete.
- Mesh refinement often reduces sensitivity to the mesh
orientation, but is not a universal remedy.
If you wish to receive the complete paper, just send me an e-mail.
CVUT / 22 May 2008 / milan.jirasek@fsv.cvut.cz