Computational Methods for Debonding in Composites

190 N. Zobeiry et al.
No Notched Strength / UnnotchedStrength
0.7 0.
0.6 0.
0.5 0.
0.4 0.
0.3 0.
0.2 0.
Ex Experimental Result
Min Mi Experiment
Max Ma Experiment
Present Pr Numerical Prediction
Present Pr Numerical Prediction
0.1 0.
0 0.1 0.20 0.3 0.40 0.5
Hole Ho Diameter / SpecimenWidth
Fig. 9.8 Comparison of experimental [29] and present numerical strength predictions of open hole
panels under uniaxial compression
9.5 Non-local Approach
9.5.1 Limitations of Local Damage Models
As stated earlier (see Sect. 9.1) the Bazant’s crack band approach used in conjunction
with the local damage model, CODAM, is only applicable to a limited class of
problems. The following are a list of some of these limitations:
• The crack band method is based on the premise that the damage localizes into a
zone with a certain height. This is valid only in quasi-static loading of notched
specimens; otherwise the scaling concept used in the crack band approach does
not apply.
• Crack and damage tend to grow parallel to the mesh orientation. In other words,
the results of the FE simulation using the local crack band formulation leads to
mesh orientation dependent results. As a result, this method can practically be
used only when the crack path is known in advance.
• To achieve more realistic results in terms of local displacements, strain and stress
fields, the height of elements should be close to the actual height of damage
observed in the experiments. For example, using elements that are much coarser
than the damage height result in under-prediction of strain and stress gradients
in the vicinity of the notch. Conversely, by virtue of the required scaling of the
softening portion of the stress-strain curve used in the crack band approach, finer
elements lead to unrealistically large strains in damaged elements.
To overcome the above limitations, other numerical approaches that address the
localization problem, such as non-local regularization, need to be adopted.
0.6