2.3. Fracture toughness and fracture loci
The link between fracture toughness R and fracture loci is based
on the assumption that there should be a connection between the
specific essential work of fracture, which characterizes the ability
of a sheet to resist crack initiation, and the work required locally
to nucleate or propagate (under continuous nucleation) a crack in
tension or shear stress loading conditions.
As discussed by Atkins and Mai (1985), the specific essential
work of fracture R may be converted to a local work done per unit
of volume atthe crack tip by dividing R by the height h ofthe necked
down process region. In case of the double notched test specimen