Damage-enhanced creep and creep rupture in fiber composites
- Virginia State Univ., Blacksburg, VA (United States)
Creep in fiber composites at high temperatures is an important phenomenon that can lead to accelerated failure in several different ways. For systems with matrix creep rates larger than those of the fibers, creep transfers load onto the fibers and the fibers undergo progressive damage under the increasing load. This leads to enhanced composite creep rates, relative to non-breaking fibers, in both ceramic and metal matrix composites. In metal composites, creep rupture can then occur by excessive damage accumulation even in the absence of explicit high-temperature fiber degradation mechanisms. In ceramic composites, creep rupture occurs following fiber degradation such as slow crack growth, a process accelerated by the enhanced stress on the fibers. Here, these phenomena are discussed within the framework of the composite model of Curtin, which is generalized to include creep and creep rupture. The model generally accounts for the statistical evolution of fiber damage and for the interfacial slip between fibers and matrix that occur in both CMC and MMC materials, both of which can be functions of time at elevated temperatures. Application of the theory to creep rupture in titanium matrix composites reinforced with SiC fibers shows good agreement with experimental results for creep rates and failure times versus applied load. Application to creep rupture in ceramic matrix composites in which the fibers undergo slow crack growth demonstrates the dependence of lifetime on load and crack growth rate. A much longer lifetime for composites, as compared to the lifetime of individual fibers tested in the laboratory, is demonstrated; this is a result of the small effective gauge length of fibers in the composite relative to the typical gauge lengths tested in single fiber stress rupture tests.
- OSTI ID:
- 175208
- Report Number(s):
- CONF-950686--
- Country of Publication:
- United States
- Language:
- English
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