Failure Characterisation Of Ti6Al4V Gas Turbine
Compressor Blades
Author(s)
A. Kermanpur, H. Sepehri Amin, S. Ziaei Rad,
N. Nourbakhshnia & M. Mosaddeghfar
Abstract
In this study, the failure process of Titanium compressor blades of an industrial
gas turbine was investigated. Several premature failures occurred in the
high-pressure section of the compressor due to the fracture of the blade roots.
Macro- and micro-fractographic investigations were carried out on the fracture
surfaces. Optical and scanning electron microscopy of the blade airfoil and root
were also performed. Mechanical properties of the blade alloy were evaluated
and compared with the standard specifications. Next, a 2D finite element model
of the blade root was constructed and used to provide accurate estimates of stress
field in the dovetail blade root and to determine the crack growth initiation in the
dovetail. Based on the normal service operation of the compressor, the
centrifugal and shear forces applied to the blade-disc configuration were
considered in the model.
The experimental results showed no metallurgical and mechanical defects for
the blade materials. Microstructure of the blade root and airfoil, and hardness and
tensile properties were all comparable with those reported in the standard
specification. Fractography experiments clearly showed multiple crack initiation
sites and fatigue beach marks. Debris particles were observed on the fracture
surfaces and in the mouth of initiated cracks. The blade surface in contact with
the disc in the dovetail region showed a higher surface roughness than the other
surfaces. The numerical model clearly showed stress concentration at the corner
on the contact facet of the blade dovetail between the blade dovetail and the
wheel dovetail. Based on the results obtained, the fretting fatigue mechanism
was proposed for the premature failures.
Keywords: fretting fatigue, compressor blade, fractography, finite element
method, computer simulation.
Keywords
fretting fatigue, compressor blade, fractography, finite element
method, computer simulation.
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