Improvement of Silicon Nitride Turbine Blade Impact Resistance Under Uniaxial Compression Loading

Abstract

The inside-out ceramic turbine (ICT), a novel microturbine rotor architecture, uses monolithic ceramic turbine blades held in compression by a rotating structural shroud instead of traditional superalloy turbine blades in order to increase its maximum turbine inlet temperature (TIT) and cycle efficiency. Previous work has shown that this microturbine architecture has potential to be viable for long-term operation in normal operating conditions. However, foreign object damage (FOD) has been a major concern for ceramic turbine rotor past development efforts, and its effects on the ICT ceramic turbine blades lifespan have not been studied thus far. An experimental approach was used to characterize the effect of the ICT configuration on ceramic turbine blade impact resistance: spherical steel impactors were fired toward silicon nitride specimens simulating blade boundary conditions for both traditional and inside-out turbine layouts. Preload levels ranging from 100 MPa to 400 MPa were applied on the inside-out layout specimens to determine its effect on impact resistance. Results indicate that the inside-out turbine configuration increases the resistance to FOD over a traditional turbine configuration. For the specific conditions of this study, the specimens resisted to over five times the impactor energy when fixed at both ends. Also, results show that applying a higher compression preload on the specimens helps to resist higher energy impacts by about 50% when far from the buckling limit.