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. Consequently, the first part of this work focuses on the modeling of the constitutive response for non-proportional cyclic loading conditions. The hardening mechanisms considered here are isotropic and kinematic hardening in conjunction with a deformation-induced, formative and a rotational change of the yield surface. The latter is captured by introducing a fourth-order tensor into the von Mises yield condition. A first attempt to model such a material behavior was presented in Dafalias et al. [1]. In the second part of this work, the constitutive equations are extended by a further internal variable, the phase field (or damage) variable, to describe ductile crack growth, cf. Tsakmakis and Vormwald [2]. It is assumed, that the underlying crack growth mechanism is driven by plastic deformation and a damage evolution equation from classical continuum damage mechanics is adapted. Both parts of the proposed model are formulated thermodynamically consistent and corresponding material parameters are calibrated experimentally. Finally, the capabilities of the proposed model are analyzed with the help of experimental results. Numerically predicted and experimentally determined crack paths in thin-walled tubes under combined tension/compression and torsional, cyclic loading are compared. In particular, both, proportional and non-proportional loading conditions are investigated. The comparison of experimental and numerical results shows that, for proportional loading conditions, there is only a quantitative influence of the hardening with respect to the crack growth rate. For non-proportional loading, however, there is a significant influence on the hardening mechanisms concerning the predicted crack paths. REFERENCES [1] Dafalias Y.F., Schick D., Tsakmakis Ch., A simple model for describing yield surface evolution during plastic flow. Deformation and Failure in Metallic Materials, 169-201, 2003. [2] 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