An inverse analysis method for determining abradable constitutive properties

Abstract

Abradable coatings enable small tip clearances within gas turbine engines to be achieved. These coatings allow blades to cut their ideal paths during engine running-in and act as a sacrificial layer during unforeseen blade-casing interactions, minimising any damage to the blades. Abradables are often plasma sprayed and as a result, a given abradable can have a wide range of properties which are defined by its composition and the spray process parameters. These properties are also known to evolve during blade-casing interactions as a result of excessive heating and compaction. In industry abradables are often characterised by a superficial Rockwell hardness value, and it is not clear how the Rockwell hardness relates to the mechanical properties of the abradable or is this relationship is unique. An inverse methodology is presented for obtaining these properties via simulated Rockwell hardness testing. Firstly, a neural network (NN) is trained using the simulated Rockwell tests, which is then used in conjunction with a particle swarm optimisation (PSO) to estimate abradable properties for a given hardness value. These properties determined form the optimisation process are then used to conduct a series of blade-casing interaction simulations, demonstrating how the contact forces and dominant frequencies differ during rub events. This work provides a methodology to rapidly estimate abradable properties over their full range of acceptable hardnesses, which can in turn be used to optimise specific blade geometries and abradable hardnesses to produce optimal compressor performance and blade life. • Inverse optimisation method to predict abradable constituent properties from a single Rockwell Hardness measurement. • Abradable hardnesses vary between spray batches and the variability of abradable properties with hardness is shown. • Blade-Casing interaction simulations demonstrate how small changes in abradable properties alter the blades response. • The constituent properties of an abradable are shown to greatly affect the contact forces during blade-casing interaction.