Search

[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.

Fatigue failure is a leading concern for many applications involving structures for transportation, manufacturing, medical devices, and electronic components. Recent advances in modeling and simulation, coupled with in situ experimental techniques, have enhanced the understanding required to distinguish and characterize mechanisms of fatigue crack formation and early growth at scales of underlying microstructure. In particular, microstructure substantially influences high cycle fatigue resistance and contributes to variability of the fatigue response. This paper reviews the confluence of recent experimental and modeling advances aimed at understanding and modeling of the formation and early growth of fatigue cracks with size on the order of dominant microstructure attributes., The original document contains color images. Prepared in collaboration with the Woodruff School of Mechanical Engineering and School of Materials Science & Engineering, Georgia Institute of Technology, Atlanta. Published in Current Opinion in Solid State and Materials Science, 2014.

This paper provides some background and historical review of how microstructure-sensitive finite element simulations can play a role in understanding effects of stress amplitude, R-ratio, and microstructure on fatigue crack formation and early growth at notches, including pores and non-metallic inclusions for Ti alloys and Ni-base superalloys. Fatigue indicator parameters (FIPs) are computed over finite volumes that relate to processes of fatigue crack formation and early growth at the scale of individual grains. It is argued that both coarse scale (uncracked, mesoscale) and fine scale FIPs (computed in the vicinity of cracks in single grains or crystals) can be related to the cyclic crack tip displacement that serves as a driving force for crystallographic fatigue crack growth, and that the fine scale FIPs correlate directly with cyclic crack tip displacement. Scatter in HCF and VHCF is computationally assessed using multiple statistical volume elements and the distribution of FIPs of extreme value character. The concepts of marked correlation functions and weighted probability density functions are reviewed as a means to quantify the role of multiple microstructure...