A Durability and Damage Tolerance (D&DT) analysis of an S200 Nicalon/SiNC CVI SiC/SiC attachment joint was conducted to determine the CMC components material structural integrity during service loading. A building block validation strategy is proposed that includes: (i) Room, and High Temperature (RT/HT) testing with AE (Acoustic Emission) and ER (Electrical Resistivity) strategies; (ii) Advanced multi-scale modeling; (iii) Interpretation test/model; and (iv) ASTM draft submittal of simplified beam equation supported by FEM/test compliance and round robin exercise.
The following building block calibration, verification, validation, and accreditation strategy were performed: 1) Material characterization analysis to determine the damage evolution under uniaxial tensile loads and compared with test; 2) Crack Growth Resistance (CGR) analysis and test of wedge loaded DCB (Double Cantilever Beam) to determine the crack growth length, zig-zag pattern, fracture, shift in failure mechanisms and derivation of fracture energy vs. crack length simple formulation at RT; 3) Joint loading multi scale modeling and comparison with observed test load displacement curve, and determination of fracture energy; and 4) blade structural integrity and response under service loading using Multi-Scale Progressive Failure Analysis (MS-PFA) and determination of contributing damage and delamination types and their locations. FE based MS-PFA of the material and structure studied addressed the critical damage events (damage initiation, damage propagation, fracture initiation, and fracture propagation) as the components were being loaded. All dehomogenized multi scale methods CMC parameters were implemented in the material and structural modeling strategy, such as crack density effects and architecture (2D, 3D orthogonal, and mixed) interphase thickness, and interfacial shear strength. Many parameters that contribute to specimen failure including interface coating thickness, mixed mode failure evolution, interlaminar defects, delamination damage, crack bridging, and fiber fracture were all studied in detail in this work. Several FE-based multi-scale modeling techniques were investigated: a) MS-PFA; b) Virtual Crack Closure Technique (VCCT); and c) integrated damage and fracture evolution methodology using combined MS-PFA and VCCT.
