Effects of flaws on fracture behavior of structural ceramics
We evaluated the effects of fiber coating thickness, fiber orientation, and elevated temperature on flaw morphology and mechanical properties of Nicalon-fiber-reinforced SiC matrix composites with fiber cloth lay-up sequences of 0{degree}/45{degrees}, 0{degree}/20{degrees}/60{degrees}, and 0{degree}/40{degrees}/60{degrees} and fiber coating thicknesses of 0. 2 and 0.4{mu}m. For the three fiber cloth lay-up sequences (0{degree}/45{degrees}, 0{degree}/20{degrees}/60{degrees}, and 0{degree}/40{degrees}/60{degrees}), mechanical property (first matrix cracking stress, ultimate stress, and work of fracture) initially increase with coating thickness and reach peak values at a coating thickness of 0.2{mu}m. A further increase in coating thickness does not result in further improvements in mechanical properties; this is related to the role of coatings in protecting fibers from damage during composite processing. Measured values of strength and work-of- fracture of the above composites at elevated temperatures increased with temperature up to 1200{degrees}C, but decreased at higher temperatures. This decrease is correlated to in-situ fiber strength and fiber/matrix interface degradation. Correlations between model prediction and measured room-temperature ultimate strength of composites with 0{degree}45{degrees} and 0{degree}/40{degrees}/60{degrees} lay-up sequences were established by using in-situ fiber strength characteristics. The failure modes and degradation mechanisms in hot-gas filters and ceramic composite joints are being characterized by the mechanical and fractographic evaluation techniques established thus far. Correlations of these results with those of nondestructive evaluation can provide critical information for improved quality control.
- Research Organization:
- Argonne National Lab., IL (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 237333
- Report Number(s):
- ANL/ET/CP--89773; CONF-9605167--2; ON: DE96011128
- Country of Publication:
- United States
- Language:
- English
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