4.2. Assessment of theoretical and experimental fracture loci
Fig. 7 shows the finite element predicted distribution of effective
strain for two double-notched test specimens taken from Table 2.
As seen,the plastic deformation region has a slightly elliptical shape
and the necked down zone where material experiences high values
of effective strain is limited to a small volume located in-between
the notches with an average height h < d. This result corroborates
the assumption h ∼= t that was previously made in the analytical
development of Section 2.2.
Fig. 8a shows the experimental strain loading paths in the principal
strain space for the double-notched test specimens loaded in
tension and plane torsion. The open markers correspond to values
that were obtained from in-plane strain measurements with
the Aramis commercial system whereas the solid markers correspond
to ‘gauge length’ strains at fracture that were obtained from
through-thickness measurements along the cracks.
The strain loading paths given by the two lines (please notice
that one of these lines is coincident with the vertical axis) correspond
to the finite element estimates provided by the test
specimens that are shown in Fig. 7. The agreement between experimental
and numerically predicted strain loading paths is good up
to the transition of experimental data from necking to fracture,
which is plotted in a simplified manner as a change into vertical
direction (refer to the vertical dashed lines in Fig. 8a). In fact, finite
elements were not able to model the change of the strain loading