Increase of Fracture Resistance by the Interaction of Two Cracks - Cohesive Law Scale Effects

The increase of the fracture resistance of a layered structure by adding weak
layers is examined through a finite element model containing two cracks. The cracks are
modelled as cohesive zones. The cohesive law parameters, such as the critical opening
relative to the specimen size, introduce scale effects. It is shown that a maximum increase
of the fracture resistance can be attained for certain cohesive law parameters even when
the distance between the two cracks is relative large relative to the structure dimensions.