|
Non destructive evaluation (NDE) is a critical technology for improving the quality of a component in a cost-sparing production environment. NDE detects variations in a material or a component without altering or damaging the test piece. Using these techniques to improve the production process requires characterization of the faults and their influence on the component performance. This task depends on the material properties and on the complexity of the component geometry. Hence, the NDE technique is applied to study the structural durability of ceramic matrix composite materials used in gas turbine engine applications. Matrix voids are common anomalies generated during the melt infiltration process. The effects of these matrix porosities are usually associated with a reduction in the initial overall composite stiffness and an increase in the thermal conductivity of the component.
Furthermore, since the role of the matrix as well as the coating is to protect the fibers from the harsh engine environments, the current design approach is to limit the design stress level of CMC components to always be below the first matrix cracking stress. In this study, the effect of matrix porosity on the matrix cracking stress is evaluated using a combined fatigue tensile testing, NDE, and 3 D image processing approach. Computed Tomography (CT) is utilized as the NDE technique to characterize the initial matrix porosity’s locations and sizes in various CMC test specimens. The three dimensional volume rendering approach is exercised to construct the 3 D volume of the specimen based on the geometric modeling of the specimen's CT results using image analysis and geometric modeling software. The same scanned specimens are then fatigue tested to various maximum loads and temperatures to depict the matrix cracking locations in relation to the initial damage. The specimen are then re-scanned and checked for further anomalies and obvious changes in the damage state. Finally, rendered volumes of the gauge region of the specimen is generated and observed to check damage progression with increasing cycles. Observations and critical findings related to this material are reported.
|
