ENVIRONMENTAL DEGRADATION AND MICRO-CRACK FORMATION IN CERAMIC MATRIX COMPOSITES WITH EBC FOR AIRCRAFT ENGINE APPLICATIONS

摘要

To save cost, weight, increase efficiency and reduce emissions of aircraft gas turbine enginesceramic matrix components are being used for nozzles, rotating blades, and combustor liners.Models of CMC constituent and micromechanical behavior subject to a wide variety ofenvironmental and thermo-mechanical conditions were formulated based on theory and test data.The GENOA code for multi-physics multi-scale durability and damage tolerance (D&DT)assessment was enhanced by implementing these key environmental degradation mechanics andwas used to predict long-term environmental effects of CMC components under expected gasturbine engine service conditions. Under an Air Force Phase I contract the feasibility of themodels were demonstrated and validated with comparisons to many material and componentlevel tests. The models can aid in the design of robust CMC components, reduce cost and risk,and allow maintenance schedules to be set up. Prediction of recession, global oxidation (oxidebuild up), crack density formation, discrete oxidation, fiber rupture (creep) behavior, low cyclefatigue, and interphase mechanics were computed for several SiC/SiC composite systems [N24A= Sylramic iBN/MI, f-CVI CVI-PIP, and CG Ni/PyC/E-SiC (w and wo EBC)] and a C/SiC[A500] composite subject to exposure at various temperature levels [RT, 550, 600, 750, 900-1000, 1204, 1350, 1450°C], humidity levels [0, 20, 60%], pressure levels [vacuum, 1, 1.5, 10, 15atm], salt-fog cycles and for vacuum and air simulating engine conditions in a burner rig andusing actual engines in field tests. Simulations were in agreement with test.