Failure investigation of fatigue crack initiation and propagation in compressor blade

Abstract

Blades are integral components of gas turbines and are subjected to critical conditions, bearing radial forces resulting from rotation. Additionally, they directly interact with high-pressure air. This research investigates the failure of GE-Frame9 compressor blades through experimental analyses. Chemical analysis, metallography, and fractography were performed on the fractured blades. The causes of failure in the first-row blades included rubbing with the casing and bending in the opposite direction of rotor rotation. Furthermore, four rows of compressor blades were extensively damaged, with some breaking at the root area. During the turbine overhaul, a shim plate was placed between the compressor blades' root and disk. Metallography confirmed that placing the shim at the blade-disc connection point resulted in stress concentration at blades root. Fractography of the fractured blade surface indicated signs of fatigue failure, and a correlation was found between the crack initiation site and the impact of the shim plates on the blade root. Fatigue crack initiation occurred due to stress concentration caused by the shim's edge, propagating through the blade root during turbine operation and ultimately leading to complete fracture. These results emphasize the importance of avoiding the placement of shims on inclined surfaces of blade roots and ensuring full contact between the surfaces to prevent stress concentration and subsequent failure.