Assessment of fatigue crack paths in single crystals from turbine blades

Abstract

[EN] Fatigue failures in turbine blades are a pervasive, unresolved economic and safety problem that is leading the structural integrity concern in both Civil and Military Aerospace engines. The high temperatures and the harmful operating environment that blades face in service coupled with the anisotropy of the single crystal nickel-based superalloys converts the fatigue analysis of a turbine blade into an even more intricate matter. As a result, it is necessary to simplify the problem and analyse it under controlled conditions. In an attempt to contribute to the aforementioned, this project explores the change in orientation that fatigue cracks undergo as they grow in notched single crystals. The analysis involves the calculation of the shear stresses resolved on the slip systems as well as the detection of single slip or multislip regions along the crack path. Two models have been created to address the problem: a simplified model without growing the crack and a more complex model growing the crack. Results are provided as i) the evolution of the shear stresses resolved on the slip planes along the crack path (RSS graph) and ii) the fluctuation of Q factor along the crack path (Q factor graph). The simultaneous analysis of both explains the crack path deviations. However, no single slip regions have been found among the specimens analysed due to the low cycle fatigue testing condition. The findings and recommendations of this project may be used to optimise blade design and eventually predict crack path.

[ES] Este proyecto investiga los cambios en los campos de tensiones y deformaciones a medida que las grietas se propagan en aleaciones monocristalinas por medio de simulaciones con el código de elementos finitos Abaqus. La orientación de los cristales así como la probabilidad de cambiar el camino de grieta con el tamaño de la grieta son analizados.