A Crystal-Plasticity Finite Element Framework to Assess the Fatigue Behavior of Turbine Blades Through Geometrically Necessary Dislocations Criteria and Conform Meshes

This current work is dedicated to the study of aircraft engine turbine's blades made in a directionally solidified nickel-based alloy. Due to its complex manufacturing process and to empirical conservative quality criteria of the manufacturer, numerous blades are scrapped. The versatility of the finite element method is used to model a whole aircraft engine turbine blade at the grain scale to quantify its fatigue behavior. This framework relies on a crystal plasticity large strain model, involving a multiplicative decomposition of the transformation. Plasticity is embodied by dislocation theory, in which both statistical dislocation and geometrically necessary dislocation (GND) densities are represented. A Kocks-Mecking law and the Orowan relation are used to quantify the plastic flow. The GNDs are computed through the curl of the plastic strain and projected on the sliding systems. In previous works [1], a monotone behavior was defined to represent tensile stress tests on equiaxial REV. This work is dedicated to improve this law by adding a kinematic hardening [2] to explicit fatigue behavior of columnar REV. Fatigue Indicator Parameters are developed based on the dislocation densities to define lifespan criteria.

References

1. C. Bovet, V. Chiaruttini, and A. Vattré, Full-scale crystal plasticity modeling and data-driven learning of microstructure effects in polycrystalline turbine blades, 2025, https://doi.org/10.2139/ssrn.5984981.
2. C. Bayley, W. Brekelmans, and M. Geers, A comparison of dislocation induced back stress formulations in strain gradient crystal plasticity, International Journal of Solids and Structures, 43(24):7268-7286, 2006, https://doi.org/10.1016/j.ijsolstr.2006.05.011.