Impact Design Methods for Ceramic Components in Gas Turbine Engines

Abstract

Garrett Auxiliary Power Division of Allied-Signal Aerospace Company is developing methods to design ceramic turbine components with improved impact resistance. In an ongoing research effort under the DOE/NASA-funded Advanced Turbine Technology Applications Project (ATTAP), two different modes of impact damage have been identified and characterized: local damage and structural damage. Local impact damage to Si3N4 impacted by spherical projectiles usually takes the form of ring and/or radial cracks in the vicinity of the impact point. Baseline data from Si3N4 test bars impacted by 1.588-mm (0.0625-in.) diameter NC-132 projectiles indicates the critical velocity at which the probability of detecting surface cracks is 50 percent equalled 130 m/s (426 ft/sec). A microphysics-based model that assumes damage to be in the form of microcracks has been developed to predict local impact damage. Local stress and strain determine microcrack nucleation and propagation, which in turn alter local stress and strain through modulus degradation. Material damage is quantified by a “damage parameter” related to the volume fraction of microcracks. The entire computation has been incorporated into the EPIC computer code. Model capability is being demonstrated by simulating instrumented plate impact and particle impact tests. Structural impact damage usually occurs in the form of fast fracture caused by bending stresses that exceed the material strength. The EPIC code has been successfully used to predict radial and axial blade failures from impacts by various size particles. This method is also being used in conjunction with Taguchi experimental methods to investigate the effects of design parameters on turbine blade impact resistance. It has been shown that significant improvement in impact resistance can be achieved by using the configuration recommended by Taguchi methods.

Quasistatic indentation and spherical particle impact studies of turbine-grade silicon nitrides

“…In other words, in the case of a gas turbine, if its engine could be operated at the temperature of the flame, the engine would achieve the maximum efficiency. Since ceramics, such as silicon nitrides, can maintain high strength a t relatively high temperatures, they are being seriously considered for structural components of high-temperature gas turbines and automobile engines (Sugawara andSugiura 1999, Tsutsui et al 2000).…”

A single, small particle launch system by electrothermal gun and microsabot

“…For example, several cases on impact of foreign object damages ͑FODs͒ have been reported in literature on ceramic gas turbines. 2 Therefore, when we utilize ceramic materials as elements of heat engines, we must know much about impact behavior of those materials at elevated temperatures in addition to that at room temperature. Knowing such behaviors is necessary for establishing safety design technique and for keeping reliability of the engines with ceramic components.…”

FOD Simulation for Ceramic Turbine Blades

“…9) Although, much work has been published on local damage, [10][11][12][13][14] there is little published on structural damage. 6,8) During test runs of a 300-kW class CGT during the New Sun Shine Project, 1) the trailing part of the ceramic rotor blades was often broken. 7,8) In this rotor configuration, most foreign particles hit the upper, leading edge area of the rotor blade.…”

“…Actually, impact of foreign objects is often reported as causing damage to CGT blades (Foreign Object Damage, FOD). 6,7) The damage is classified into two types: local and structural. 6,8) Local damage describes damage generated around impact points, such as ring cracks, radial cracks, cone cracks, etc.…”

“…6,7) The damage is classified into two types: local and structural. 6,8) Local damage describes damage generated around impact points, such as ring cracks, radial cracks, cone cracks, etc. Structural damage describes other damage located away from the impact point.…”