Short-crack mechanical properties and failure mechanisms of Si[sub 3]N[sub 4]-matrix/SiC-fiber composites
- National Inst. of Standards and Technology, Gaithersburg, MD (United States)
- Univ. of Maryland, College Park, MD (United States). Dept. of Materials and Nuclear Engineering
SiC-fiber-reinforced Si[sub 3]N[sub 4] composites were fabricated by hot pressing. The indentation-strength technique was applied to study the mechanical properties of these composites. This enabled the investigation of short-crack behavior of continuous-fiber ceramic composites (CFCCs). The flaw tolerance of composite ultimate strength, matrix-cracking stress, and work-of-fracture were investigated. Scanning electron microscopy was used to examine crack-fiber interactions. The ultimate strength was found to be independent of indentation load at a fiber volume fraction f = 0.29, while at f = 0.14 it exhibited a transition from flaw-sensitive to flaw-independent. The work-of-fracture was found to be independent of indentation load at both fiber volume fractions. The matrix-cracking stress was found to correspond to the first load-drop on the load-displacement curve. It decreased with increasing flaw size and therefore is not the steady-state matrix-cracking stress. A failure mechanism transition from catastrophic failure to non-catastrophic failure, coupled with the transition from flaw-sensitive to flaw-tolerant behavior, was observed by varying the preexisting flaw size and the fiber volume fraction. These transitions were explained by analyzing the relations between ultimate strength, matrix-cracking stress, fiber volume fraction, and preexisting flaw size of the composite materials. Experimental results were compared with predictions from available models.
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 7243589
- Journal Information:
- Journal of the American Ceramic Society; (United States), Vol. 77:7, Issue 7; ISSN 0002-7820
- Country of Publication:
- United States
- Language:
- English
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