Cyclic fatigue crack growth in silicon nitride: Influences of stress ratio and crack closure
- National Research Inst. for Metals, Ibaraki (Japan). Tsukuba Labs.
The characteristics of cyclic fatigue crack growth was investigated in silicon nitride which hardly shows rising R-curve behavior, using single edge precracked beam specimens. Crack growth behavior is known to be explicable by a power law relationship including both the stress intensity range {Delta}K and the maximum stress intensity K{sub max}; i.e. da/dN = C(K{sub max}){sup p}({Delta}K){sup q}. However, when K{sub max} is a constant, the crack growth rate da/dN is found to be not a unique power law function of {Delta}K. The curve in a double-logarithmic plot of da/dN and {Delta}K is composed of two regions. The slope q in the lower {Delta}K region is larger than that in the higher {Delta}K one. The difference of the q value between the two regions is primarily responsible for crack closure. Namely, the crack growth rate for a constant K{sub max} does correlate with the range of the effective stress intensity {Delta}K{sub eff} defined as {Delta}K{sub eff} = K{sub max} {minus} K{sub cl}, where K{sub cl} is the crack closure stress intensity. It is, therefore, suggested that the crack growth behavior is expressed by a crack growth law containing the effect of crack closure, i.e. da/dN = C(K{sub max}){sup p}({Delta}{sub eff}){sup q}. On the basis of these results and other data available, cyclic fatigue mechanisms are discussed.
- OSTI ID:
- 39850
- Journal Information:
- Acta Metallurgica et Materialia, Journal Name: Acta Metallurgica et Materialia Journal Issue: 4 Vol. 43; ISSN 0956-7151; ISSN AMATEB
- Country of Publication:
- United States
- Language:
- English
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