Experiment on Foreign Object Damage of Gas Turbine-Grade Silicon Nitride Ceramic

Abstract

A new high quality turbine system using monolithic silicon-nitride ceramic is under development. In this study particle impact tests of the silicon-nitride have been tried at room and elevated temperatures with and without tensile load, which simulates centrifugal force of blade rotation. In the experiment 1 mm diameter particle is impacted at velocities up to 900 m s−1. In this paper, critical velocities for bending fracture and Hertzian cracks are examined. Moreover, strength degradation at elevated temperature and spall fracture of the blade are discussed. The main results are: 1) The bending fracture mode critical impact velocity for soft particles is higher than that for hard particles. 2)The impact parameter ϕ for initiation of Hertzian cracks ranges 1.08×10−5 – 1.56×10−5 for the materials tested. 3)Strength degradation at elevated temperature was clearly observed. 4) In the impact tests on blades spall fracture, which was caused by interaction of stress waves, appeared.

FOD Simulation for Ceramic Turbine Blades

“…The impact location is decided with reference to the past instances. 7,15) As shown in Fig. 2, the grid points are distributed rather densely near the impact point compared to further places.…”

“…The blade was cut from the ceramic rotor of a CGT-302 unit. 15) Damage observed in the impact experiment is shown in Fig. 1, 15) which clearly shows typical structural damage occurring at locations other than the impact point.…”

“…15) Damage observed in the impact experiment is shown in Fig. 1, 15) which clearly shows typical structural damage occurring at locations other than the impact point. In the experiment a 1-mm diameter samarium-cobalt (Sm 2 Co 17 ) ball was used as an impactor.…”

Application Technique and Evaluation for Functional and Structural Design of Ceramics.

“…(16) by considering an effective stress hold time, eeff, per cycle by using Eq. (3): (16) where Nf is the number of cycles to failure. Fig.…”