The aim of this research is to simulate fatigue crack propagation in ductile materials subjected to proportional and non-proportional, cyclic loading conditions. For the materials under consideration, it is expected that non-proportional hardening has a major influence on the crack initiation and further evolution. In the first part of the present work a suitable constitutive model for the description of the material behavior in such cases was proposed. The plasticity part of the model is now further extended by a phase field variable as described in Tsakmakis and Vormwald [1] to capture the complex crack phenomena. The underlying crack growth mechanism is assumed to be driven by plastic deformation. Thermodynamic consistency of the model is ensured in the present work within the framework of so-called non-conventional thermodynamics. Finally, the capabilities of the proposed model are analyzed with the help of experimental results. To this end, numerically predicted and experimentally determined crack paths in thin-walled tubes under combined tension/compression and torsional, cyclic loading are compared. In particular, non-proportional combinations of the aforementioned loads are analyzed. References [1] Tsakmakis A., Vormwald M., Phase field modelling of ductile fracture in the frameworks of non-conventional thermodynamics and continuum damage mechanics. International Journal of Solids and Structures, 262:112049, 2023