Effects of thermal and mechanical combined load on blade stress and fatigue life characteristic

The turbine blade is the most important component in the heavy-duty gas turbine. The common fatigue failures of the blade include the thermal fatigue and mechanical fatigue. Firstly, the finite element simulation of the blade is carried out in the working condition including the centrifugal load, high frequency vibration load and thermal load. According to the simulation results of the combined load, the stress distribution of the blade body is reasonable in the working condition load; the stress level on the blade suction surface is higher than the pressure surface; in the blade body, the maximum Von Mises stress is 699.87 MPa, and the location of the minimum fatigue life is close to the blade shroud. Above simulation results is very useful for the structural design and fatigue experiment. Secondly, the blade fatigue experiment is realized by building a thermo-mechanical combined fatigue experiment system. The stress and thermo-mechanical fatigue life characteristic are both analyzed with this experiment system. Through the dynamic stress experiment under the high and low cycle combined load, the stress-time history in the blade body is obtained; through the thermo-mechanical fatigue experiment, the fatigue crack of the blade first appears in the middle of the blade exhaust side. Based on these experiment results, the dynamic stress experiment data and the combined fatigue failure mode are obtained. Lastly, a nonlinear Gauss fitting expression between the fatigue life cycle number and the vibration frequency of the high cycle load is given for the fatigue life prediction. These results are significant for the blade fatigue failure in the future.