Foreign Object Damage and Fatigue Strength Loss in Compressor Blades

Abstract

Foreign object damage (FOD) is always an all-important problem of gas turbine engines safety, reliability and operating costs. This paper describes experimental and numerical prediction investigations of FOD to compressor blades of gas turbine engine. Experimental modeling of FOD processes was done using a special plant on the base of a pneumatic gun. Real steel blades of a high-pressure compressor were impacted with spherical steel projectiles at the velocity about 200 m/s. Typical in-service damages as well as round dents, tears and bends were reproduced in the experiment. Numerical prediction analyses of the damage process were fulfilled by finite element method (FEM). Material behavior is described with elastic-plastic strain rate dependent model. We find the form and sizes of the calculated damages to be in good agreement with the experimental findings. Furthermore, the experimental and computational procedure for estimation of fatigue strength loss of damaged blades is proposed. It is based on study of stress concentration in damages. Stress concentration factor for different concentrator shapes was calculated using 3-D finite element analyses and refined via a stress concentration sensitivity factor. Stress concentration sensitivity factor was experimentally defined through fatigue tests of real blades with V-shape notches at leading edge. This technique supposes minimum laborious fatigue tests. Experimentally confirmed numerical methodology and model may be used for prediction study of FOD and fatigue strength loss of gas turbine engine blades.