Creep/Fatigue Tests on Full Scale Hollow Turbine Blades Considering Temperature Gradient

Abstract

Working in a harsh environment with high temperature gas and high rotation speed, hollow turbine blades of gas turbine engine commonly endure both creep damage and low cycle fatigue damage at the same time. It is difficult to predict the life of hollow turbine blades accurately because of a strong coupling effect between creep and low cycle fatigue (creep/fatigue) damage. To address this difficulty, one effective way is to carry out creep/fatigue tests on full scale hollow turbine blades in a bench environment. The present creep/fatigue test methods on full scale hollow turbine blades usually do not consider the temperature gradient between the wall of cooling hole and blade surface. It does not matches the actual working circumstance of hollow turbine blades, under which the temperature gradient at the blade body can reached 150°C or even more higher. This investigation proposes a new experimental setup of creep/fatigue tests on full scale hollow turbine blades, in which real hollow turbine blades are heated by the eddy current induction heating furnace and cooled by cooling air which goes through the hollow blade’s cooling hole. During the tests, the temperature gradient between the wall of cooling holes and blade surfaces were controlled by adjusting the power of eddy current induction heating furnace and the flux of cool-air. Several thermocouples are employed to measure and validate the temperature gradient at the key/critical section, among them three are embed inside the wall of cooling hole by cutting the hollow turbine blade along cooling hole into three parts, and two are glued on the blade’s surface. Tests results show that, when the eddy current induction heating furnace is working stably with an output power of 6.4 Kw and meanwhile the flux of cooling air which goes through the hollow turbine blade’s cooling hole reaches 10 liter per minute, the temperature gradient of the hollow turbine blade at the key/critical section can be well simulated in a bench environment. Eight full scale hollow turbine blades have been tested at four different stress levels in this investigation. The test data are processed to obtain the field life based on equivalent damage principle. The field life data of the hollow turbine blades fits well with that of their flight experience.