Investigation of wear mechanisms in AlSi-polyester abradable - Ti(6Al4V) blade contacts using stroboscopic imaging

Abstract

Abradable linings in aero engines have been an area of research interest over the past few decades as small reductions in clearances between stationary and rotating parts can lead to large increases in engine efficiency. The work performed in this article focuses on characterising the blade wear behaviour in contacts between Ti (6Al 4V) blades and AlSi-polyester abradables. This was done by performing three abrasion tests on the new test rig developed at the University of Sheffield. Tests have been performed on the AlSi-polyester abradables of the same nominal hardness over two incursion rates – 0.02μm/pass and 0.2 μm/pass and two blade tip speeds – 85 m/s and 170 m/s. The front-on stroboscopic imaging technique was used for these tests, which allowed capturing images of the entire blade front for a number of blade strikes during a test. It was found that at the incursion rate of 0.02μm/pass, both adhesions to the blade surface and blade wear were observed across the blade width. It was observed that adhesions were more likely to gradually wear off rather than fracture at 0.02μm/pass, and, fracture at 0.2 μm/pass. Tested surface profiles were obtained using an Alicona non-contact measurement system. This allowed the comparison of the blade profile results from the blade images to the surface of the respective tested abradable sample. It was concluded that adhesions that fractured could contribute to the localized gaps between the final blade and the final abradable surface where such adhesions have fractured close to the end of a test. Further testing areas have been identified such as the investigation into the effects of parameters such as incursion rate of a blade into an abradable, blade tip speed and abradable hardness on the results. The developed front-on imaging system also opened a possibility to investigate in-situ the rub performance of blades of varying tip geometry.