An inverse method based on combined high-and-low cycle fatigue (HCF/LCF) tests and the outfield practical failure data was developed to estimate the vibration stress of the turbine blade in working condition.All the test specimens of the turbine blades owned the same production procedures as the outfield failure blades.Two groups of HCF/LCF tests were performed

one was median life test at six vibration stress levels

and the other was life dispersion test at a given vibration stress level.Then

P-S-N curves were extrapolated with the maximum likelihood method.Finally

vibration stress of the turbine blade in working condition was determined by the P99.87%-S-N curve combined with the statistical life of the outfield practical failure data.