Thermal Fatigue Strength of Gas Turbine Rotor Disc

Abstract

One of the problems most vital to the strength of the rotor disc of gas turbine for naval ships is its thermal fatigue fracture due to the plastic strain which occurs each time the engine is started and stopped. For the estimation of how often the turbine can be started and stopped without causing the thermal fatigue fracture, it is necessary to know the magnitude of plastic strain which repeatedly occurs at every part of the rotor disc. Therefore, first we worked out, by solving a partial differential equation concerning the heat transfer, the transient temperature distribution taking place in the disc before the status of its interior becomes almost steady after the turbine has been started, and in order further to know the change with time in the status of stress and plastic strain in the disc, we, on the basis of the transient temperature distribution, worked out the elasto-plastic solution of the fundamental equation on the rotor disc, using the finite strain theory and the trial and error method (so-called S.S. Manson's method). Thus we could calculate the magnitude of the plastic strain. At the same time, we made a constant strain fatigue test of the material of rotor, and from the results obtained it was presumed that the rotor disc would stand 400-1700 times of starting and stopping of the turbine at the lowest estimate, thus proving that this gas turbine is fully serviceable as a buster.