Date of Award

4-28-2022

Publication Type

Thesis

Degree Name

M.A.Sc.

Keywords

Abradable;Characterization;Material Properties;Materials;Strain Rate;Temperature

Supervisor

Aleksandr Cherniaev

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Abstract

Certification of an aircraft turbofan engine requires the demonstration of its ability to contain a fan blade should the blade accidentally separate under critical operating conditions. Significant efforts have been made by the industry in creating high-fidelity full-engine numerical models for pre-certification simulations of blade-off scenarios to ensure engine certification via only one physical test, thus enabling multimillion-dollar cost avoidance. In the areas adjacent to the rotating fan blades, a fan blade containment system of an engine is usually supplemented with a lightweight abradable rub strip material. The abradable’s main function is to minimize the clearance between blade tips and the fan case. However, the interaction between the released blade and the layer of abradable material during the fan blade-off event can significantly influence blade orientation and trajectory and, therefore, may have a pronounced effect on all subsequent phases of the process and resulting damage to engine components. Therefore, the availability of a physics-based constitutive material model for abradable materials and its representation in the full-engine numerical models is highly important for the accuracy and reliability of predictions of the fan blade-off simulations. This study focused on the very first and the most critical step in the development of such a constitutive material model, namely the physical characterization of two distinct abradable systems currently used in turbofan engines. Compositional analysis of both abradables was conducted using scanning electron microscopy, which enabled formulation and development of a test program; manufacturing procedures for test specimens were developed and fine-tuned. Both abradable materials were tested under quasi-static (tension, uniaxial and confined compression), elevated temperatures (tension and compression), and high strain-rate (tension and compression) conditions. Despite compositional differences, both studied materials exhibited unequal resistance to tensile and compressive loading (compression strength higher than tensile), as well as significant temperature softening in the range of temperatures between 20 and 120°C. Abradable 1 was found to be strain-rate sensitive in compression, while Abradable 2 did not demonstrate such sensitivity, as follows from a comparison of quasi-static and ~1000/s strain rate test results. In addition, Abradable 1 demonstrated foam-like behaviour (stress plateau on the stress-strain diagram) when subjected to confined compression loading. Modelling implications following the test results were formulated and future work was discussed.

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