z) displacements, leading to the interdependence of SIFs for Modes I, II, and
III. Results are presented for a center-cracked BD specimen, with two specific
crystallographic orientations. The crack plane for the first specimen is (111)
and the crack direction is [o101. For the second specimen the crack plane is
again (111), while the crack direction is [121]. There are important reasons for
choosing these two specific BD specimen configurations. These two crack directions
typically represent the fastest and the slowest crystallographic crack growth rates,
respectively, on the { 111} family of octahedral planes, and hence have important
implications on estimating fatigue crack growth life for single crystal components
[2, 37]. Even if cracks nucleate on other planes, because of local influence from
intrinsic defects such as micropores, carbide particles and undissolved eutectics,
they tend to migrate to the octahedral planes, in the primary slip directions ((101)
family of directions), since they represent the paths of least resistance for crack
propagation [2]. Results presented show that SIF values are consistently higher for
the (101) crack direction, compared to the (121) direction, for same crack angles
and loads.