Fatigue strength analysis of an axial compressor blade using the modified Locati method

Abstract

The Locati method for accelerated fatigue testing can be successfully applied in preliminary fatigue testing of components and in production quality control. The method uses only one test sample and assumes that the slope of the SN curve is known a priori. In this paper, a modified Locati method is presented in which the initial approximation of the SN curve is based on the tensile strength and pseudo-fatigue limit of aluminum alloy 2618-T851. The first natural frequency is likely to be excited during the operation of an axial compressor, according to finite element (FE) modal analysis. A total of five axial compressor blades were tested by vibration exciter. The blade was excited at its first natural frequency until it failed due to a fatigue crack. After the natural frequency of the damaged blade dropped by more than 10%, failure was assumed. The fractured blade surface showed two fatigue crack areas, which occurred at the trailing edge of the blade and at the center of the convex blade surface as predicted by FE harmonic response analysis. The proposed method was successfully applied to the quality control of axial compressor blades in production.