Cyclic Fatigue Behavior of Reaction Bonded Silicon Nitride from Ambient to Elevated Temperatures. Ph.D. Thesis
The study of cyclic fatigue behavior of ceramic materials is becoming increasingly important as ceramics are being considered for structural applications. This work concentrated on the cyclic fatigue behavior of reaction bonded silicon nitride (RBSN) at room temperature, 1000 C, 1200 C, and 1400 C. Study of crack growth under static loading at these temperatures was also performed for comparison. Mechanical properties of the material were also determined from ambient to elevated temperatures to better understand material behavior under fatigue testing. Cyclic and static loading tests were conducted using the double cleavage drilled compression (DCDC) specimen. Stress intensity calibration of the specimen geometry was performed on the RBSN. At room temperature, specimens under cyclic loading were susceptible to subcritical crack growth; however, no measurable slow crack growth under static loading was observed. The mechanism of cyclic fatigue crack growth at room temperature was determined to be wedging of crack face asperities and trapped debris particles upon unloading. Local stress concentrations from the wedging at the crack faces caused microcracking and crack branching, observed by electron microscopy, which helped to extend the primary fatigue crack. Cyclic and static loading of the DCDC geometry at elevated temperatures showed increased crack growth rates with both types of loading. At 1000 C under cyclic loading crack growth rates were similar to room temperature rates. However, significant increases in susceptibility to cyclic loading occurred at 1200 C and 1400 C. Crack growth under static loading at 1000 C dramatically increased from room temperature behavior to nearly match that under cyclic loading. As temperature increased above 1200 C, static loading became more detrimental than cyclic loading.
- Research Organization:
- Northwestern Univ., Evanston, IL (United States)
- OSTI ID:
- 236785
- Report Number(s):
- N-96-21555; NIPS-96-34948; TRN: 9621555
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: Jan 1994
- Country of Publication:
- United States
- Language:
- English
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