  A framework based on FFT is proposed for micromechanical fatigue modeling of
polycrystals as alternative to the Finite Element method (FEM). The variational
FFT approach is used with a crystal plasticity model for the cyclic behavior of
the grains introduced through a FEM material subroutine, in particular an
Abaqus umat. The framework also includes an alternative projection operator
based on discrete differentiation to improve the microfield fidelity allowing
to include second phases. The accuracy and efficiency of the FFT framework for
microstructure sensitive fatigue prediction are assessed by comparing with FEM.
The macroscopic cyclic response of a polycrystal obtained with both methods
were indistinguishable, irrespective of the number of cycles. The microscopic
fields presented small differences that decrease when using the discrete
projection operator, which indeed allowed simulating accurately microstructures
containing very stiff particles. Finally, the maximum differences in the
fatigue life estimation from the microfields respect FEM were around 15% . In
summary, this framework allows predicting fatigue life with a similar accuracy
than using FEM but strongly reducing the computational cost.
