Crack branching in all-oxide ceramic composites
- Harvard Univ., Cambridge, MA (United States). Div. of Applied Sciences
The existence of oxidation embrittlement in previously developed ceramic-matrix composite (CMC) systems at intermediate temperatures (500--900 C) has motivated the development of all-oxide CMCs. Studies of the damage tolerance of an all-oxide CMC suggest that it relies on distributing fiber bundles heterogeneously in a porous matrix with a thin matrix-only region surrounding each bundle. For such composites, loading in the direction of the fibers causes cracks to first commence in the fiber bundles, breaching both the matrix and fibers within each bundle. These fiber-bundle cracks then branch in the matrix-rich region, parallel to the load, forming stable H-shaped cracks. The mechanics behind one mechanism controlling the competition between branching and continued extension of a preexistent fiber-bundle crack in a unidirectional all-oxide CMC are provided in this paper. Both plane-strain and axisymmetric cases are studied using an integral equation method as well as a numerical method based on finite elements. With no elastic mismatch assumed between the fiber and matrix, a single nondimensional combination, E{Omega}/{sigma}{sub {infinity}}, emerges as the key parameter that governs the tendency of the crack to branch (where E is Young`s modulus, {Omega} is the thermal misfit strain between the fiber bundle and matrix, and {sigma}{sub {infinity}} is the stress applied parallel to the fiber axis). Quantitative estimates of the conditions under which the branching of the bundle crack is favored are presented.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 203556
- Journal Information:
- Journal of the American Ceramic Society, Vol. 79, Issue 1; Other Information: PBD: Jan 1996
- Country of Publication:
- United States
- Language:
- English
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