Non-destructive Evaluation Methods for CMC Components

Abstract

The assessment of flaws, material damage and mechanisms which encourage the propagation of damage belongs to the most challenging objectives for non-destructive evaluation when applied on inhomogeneous microstructures like that of ceramic matrix composites. The operative point is the distinction between unavoidable or even desirable features of microstructure and failure critical elements which may initiate the formation of serious component damage later on. So far the lack of an established knowledge base for the classification and validation of microstructural features makes it almost impossible to predict the material’s behavior under certain thermo-mechanical load scenarios and therefore its lifetime expectation. With the C/C-SiC composite material which is manufactured by using the three step liquid silicon infiltration process, there is a widespread variability of microstructures and material properties which depend to the chosen fabrication parameters. Though there is a whole bunch of non-destructive inspection techniques available, it still remains very difficult to drive the right conclusions from the analysis data. While most of the well proven non-destructive evaluation analysis techniques as for example ultrasound mapping, radiography inspection or lock-in thermography imaging still demand a relatively high level of experience for proper measurement interpretation, the 3-dimensional computed tomography technique offers much more information density with by far higher resolution of the inner structure of the investigated object. Therefore the danger of misinterpretation of microstructural anomalies or material flaws is almost negligible. However, with increasing measurement information it becomes even more difficult to evaluate the consequences that may result from the observed features with respect to the material’s behaviour under mechanical load. Thus, the systematical identification and quantitative classification of material defects and failure critical design elements of structure components as part of a reliable quality assurance system is a goal of highest priority.