Slow crack growth from controlled surface flaws in hot-pressed Si/sub 3/N/sub 4/
- Systems Research Laboratories, Inc., Dayton, OH
The elevated-temperature slow-crack-growth behavior of HS-130 Si/sub 3/N/sub 4/ was studied by extending ''controlled'' surface cracks in bars loaded in 4-point bending. Several such noninteracting cracks were produced on the tensile surfaces of bend bars by Knoop microhardness indentation. The stress and dimensions of the subcritically growing cracks were used to calculate the stress-intensity factor, K/sub I/, from fracture-mechanics formulas for semielliptical surface cracks in bending. The crack-growth velocity, ..nu.., was obtained by dividing crack extension by loading time interval. The data indicated very large scatter in measured velocities for given K/sub I/ values, which was interpreted as due to the interaction of the small cracks with local material heterogeneities. No simple functional relation between K/sub I/ and ..nu.. could be established for HS-130 Si/sub 3/N/sub 4/ from the ..nu..-K/sub I/ data.
- OSTI ID:
- 6515968
- Journal Information:
- J. Am. Ceram. Soc.; (United States), Journal Name: J. Am. Ceram. Soc.; (United States) Vol. 61:5-6; ISSN JACTA
- Country of Publication:
- United States
- Language:
- English
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