Assessment of performance capability of turbine blades with protective coatings after overheating events

Rotor blades of the high-pressure aircraft turbine are the most heavily loaded components of the runner wheel at high-temperature conditions. Overheating is one of the severe degradation modes and depends on the degree and time of overheating. A rather simple form of a degradation parameter D was empirically proposed by the producer in order to assess the level of blade degradation after overheating. The parameter D was recently found to well reflect the level of degradation of protective surface coatings in terms of a reduction of its relative thickness. This paper shows that the parameter D can be physically understood in terms of the Hamiltonian action S and, according to the presented numerical analysis, it possesses the best form of all possible damage indicators of the same physical meaning.