  In the present work, theoretical approaches, based on grain orientation
dependent Young's modulus and Schmid factor are used to describe the influence
of local grain orientation on crack initiation behaviour of the coarse grained
nickel base superalloy Ren\'e80. Especially for strongly anisotropic crystal
structures with large grain size, such as the investigated material, the local
elastic properties must be taken into account for assessment of fatigue crack
initiation. With an extension of Schmid's law, the resulting shear stress
amplitude, which triggers local cyclic plastic deformation, can be calculated
depending on local Young's modulus and Schmid factor. A Monte Carlo simulation
with 100,000 samples shows how random grain orientation affects these
parameters. Furthermore, the product of Young's modulus and Schmid factor
(called $E\cdot m$) is used as a parameter to determine how grain orientation
influences resulting shear stress amplitude for given total strain amplitude.
In addition to the theoretical work using that approach, this model is also
validated using isothermal LCF experiments by determining local grain
orientation influence on the crack initiation site using SEM-EBSD analyses.
