Abaqus supplies cohesive elements and several traction-separation laws
which can be used to study crack problems. In studying a mode I crack
problem (see Fig.1), the cohesive interfaces in front of the crack tips
(both sides) are represented by cohesive elements. The size of the bulk
material is taken as 6x6 mum and the size of cohesive elements is 2x2
nm (or 10x10 nm). The constitutive response in the cohesive element is
described by a triangle-type traction-separation law, where  maximum
stress or displacement is chosen as the failure criterion of the
cohesive elements. Stresses are applied on the bottom and top surfaces.

file:///home/users/zengxif4/FEM/Test-Cohesive3-gb/cfg.png�

Fig. 1 mode I crack problem 

 The material parameters are listed below:

# BULK MATERIAL 

 *Elastic
 0.398, 0.3

# Interface (cohesive zone)

 *Material, name=Adhesive2nm
*Damage Initiation, criterion=MAXE
 0.001, 0.001, 0.001
*Damage Evolution, type=DISPLACEMENT
 0.002,
*Elastic, type=TRACTION
 9.3, 9.3, 9.3

Fig. 2 shows an example of my simulations. I do see a propagation of
the crack. However, I also see that even the crack has propagated by a
certain distance, there are still some elements bundles behind the
crack tip remaining unbrocken. This makes me very confused. Can anybody
give some comments and help to clarify this problem?

file:///home/users/zengxif4/FEM/Test-Cohesive3-gb/contour.png�

 Thank you!