Failures analysis of compressor blades of aeroengines due to service

Abstract

In spite of the high levels of reliability of modern aeroengine components resulting from rigid standards and practices, failures of compressor and turbine blades during normal operational environments are common situations which compromise the flight safety. The investigation of real failures affecting these components allows gaining a deeper knowledge concerning the mechanisms of crack initiation and propagation which, in turn, can be used in order to prevent future incidents or accidents. This paper presents the analysis of two in service failures involving blades breakage belonging to different compressor stages. Crack growth mechanisms were evaluated based on the visual inspection of the affected components and with both macroscopic and microscopic observations of the fracture surfaces. The origins of crack initiation were evaluated through the examination of crack path and beach marks on the fracture surface. Mechanical analyses were carried out to identify the possible causes of the failures by examining anomalies in the mechanical behaviour of the materials such as hardness tests, chemical composition and surface coating analysis through SEM observations. The analysis of the different fracture surfaces shows that crack propagation is mainly related with fatigue mechanisms whilst crack initiation can be attributed to distinct causes, either the presence of defects in the surface of the blade due to impact of debris or intrinsic material defects or some degrading mechanisms affecting the internal microstructure of the material. In some cases the blades were in service after having being object of an overhaul procedure, which can justify some crack initiation cases that caused in service failures.