High cycle fatigue analysis of third stage blade based on shroud gap effect

Due to the very small gap of the contact relaxation, which is attributed to the abrasion of blade shrouds in the gas turbine, the fatigue failure of the blade occurs severely. So the gap effect and the high cycle fatigue properties of the turbine blade need to be studyed. Based on the theoretical calculation, the equation of the maximum value of shroud gap is given. Then through the finite element method, A modal analysis is used to determine the vibration characteristics. Meanwhile, based on a new test apparatus, the dynamic stress experiment is carried out. According to the simulation and experiment, the relationship between the gap effect and the high cycle fatigue of the third stage blade are analysed in detail. Finally, some results of the vibration characteristics and dynamic stress value are got and the relationship between the shroud gap and the high cycle fatigue damage is quantificationally given. From the above results, there is a good agreement between experiment and simulation, which shows that the gap effect on the high cycle fatigue can increase the damage and reduce the fatigue life of blades. Due to the influence of the shroud gap, the resonant frequency almost change into two times of the original one. And the experimental stress value suggests that there is a nolinear exponential relationship between the gap value and the fatigue damage ratio value.