High-Temperature Combined Fatigue Tests on Full-Scale Turbine Blades

Abstract

Compared with standard specimens, fatigue tests on full-scale turbine blades can take factors such as geometry and manufacturing process into consideration of life assessment. However, for combined fatigue tests of full-scale turbine blades, there exist two challenges. The first one is that it is difficult to apply combined loads of centrifugal force (low cycle fatigue, LCF) and vibration force (high cycle fatigue, HCF) properly because of the interaction between these loads. The second one is that it is hard to determine the range of HCF load/stress which the blade experiences at service conditions. To address these two challenges, firstly, a set of two-path fixture is designed to apply combined loads on the test blade, which can transfer LCF and HCF load separately by different paths. And secondly, two methods, i.e. the inverse method and the contrast method are proposed to estimate the HCF stress level for turbine blades at service conditions. The inverse method infers the HCF stress level by comparing blade failure data between field (in service) and bench tests conditions, while the contrast method obtains HCF stress level by comparing blade failure data between new and used blades under bench tests conditions. Detailed procedures of high temperature combined fatigue tests on full-scale blade are presented, and experimental life data is also included and analyzed.