Fiber breakage in metal matrix composites -- reality or artifact?
- Wright Lab., Wright-Patterson AFB, OH (United States). Materials Directorate
- NYMA, Cleveland, OH (United States)
How embarrassing is it when research scientists draw conclusions based on what appears to be solid evidence, and present and publish these results which ultimately are found to be incorrect? Such a situation appears to have arisen in the conclusion that a very large number of fiber breaks appear to be a characteristic of in-phase thermomechanical fatigue (IP TMF) of SiC reinforced titanium composites. What has been puzzling all along is the inability to explain the load carrying capability of 0{degree} fibers at elevated temperatures where fiber/matrix interfacial strengths are almost non-existent, where residual thermal stresses are negligible, and where multiple fiber breaks have been observed in nearly every fiber at spacings of only a few diameters. equally puzzling is the inconsistency between acoustic emission (AE) observations which indicate only a limited number of fiber break events (4) and observations on carefully polished metallographic surfaces which indicate hundreds of closely spaced fiber breaks involving nearly every fiber. To help explain these apparent discrepancies, the authors present experimental verification and a simple analysis intended to demonstrate that large numbers of fiber breaks, which they denote as pseudo fiber breaks (PFBs), do not occur under in-phase TMF, creep, or LCF. Instead, PFBs appear solely as the result of mechanical polishing procedures on specimens which have been subjected to such loading conditions and are a direct result of a state of residual tension in brittle ceramic fibers.
- OSTI ID:
- 455197
- Journal Information:
- Scripta Materialia, Vol. 36, Issue 5; Other Information: PBD: 1 Mar 1997
- Country of Publication:
- United States
- Language:
- English
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