A first glimpse into Eq. (13) allows concluding that fracture loci
derived from fracture toughness R may be seen as an effective strain
based criterion where the ellipses of constant effective strain at
fracture ε = kf in the principal strain space (refer to Figs. 1b and 2b)
are modified in order to include a dependency on fracture toughness
RI or RII, sheet thickness t and stress-strain response of the
material by means of constant K and strain hardening exponent n
(in case of a material following = Kεn).
The comparison between the fracture loci derived from Eq. (13)
and from experimental procedures based on the determination
of gauge length strains at fracture will be provided in Section 4
and will be utilized to validate the proposed link between fracture
toughness and fracture loci.