Mechanisms of incursion accommodation during interaction between a vibrating blade and an abradable coating

Abradable materials are used as inner coatings in aeronautical compressors. In the event of blade-casing interaction, the abradable coating accommodates the incursion of the blade tip in order to protect the blade and the casing from severe damage. In this study, an experiment was conducted in conditions representative of the full-scale situation in terms of velocity, temperature and the dynamical characteristics of blades. The mechanisms of incursion accommodation were investigated based on dynamical data and a post mortem analysis of the coating and the wear debris. First, dynamical blade tip incursion was estimated by considering blade vibrations and coating waviness. The tip incursion was found to be significantly different from the measured displacement of the blade foot. Next, a post mortem analysis of the coating was performed at the surface and sub-surface. Four mechanisms were identified, namely debris release, surface shearing, compaction and reversible deformation. Care was taken to provide orders of magnitude for the different mechanisms relating to residual thickness loss of the coating.