Combined low and high cycle fatigue tests on full scale turbine blades

Since the unavoidable vibrations wildly exist in the operating environment of turbine blades, the assessment of the combined low and high cycle fatigue (CCF) properties are of paramount importance for turbine blades. To study turbine blades' CCF properties accurately, one important and useful way is to carry out the CCF tests on full scale turbine blades. When conducting the CCF tests of turbine blades, there are two challenges. One is finding ways/paths to transfer the low cycle load and the high cycle load properly, and the other is the determination of high cycle vibration stress level in the working condition. In this investigation, a new experimental method, in which full scale turbine blades are loaded by a special design test system providing high cycle loads and low cycle loads without interference, is proposed to conduct CCF life tests, while an analysis method (reverse method) based on the CCF tests was developed to estimate the high cycle vibration stress level. The design of the test system and the principle of the reverse method are fully explained in this paper. Test results show that the test system can apply HCF/LCF combined loading on the key section of the full scale turbine blade, and successfully simulated the working state. Meanwhile, the working condition vibration stress range of the blade is obtained through the reverse method.