Machining Flaws and the Strength Grain Size Behavior of Ceramics.
Abstract
A model for the strength-grain size dependence of ceramics failing from machining flaws is presented based on the observation that the size of machining flaws (C) shows little or no dependence on grain size. Two regimes of behavior are seen. At finer grain sizes, little or no strength dependence on grain size (G) exists because flaws are greater than G. For large G, the significant decrease of strength with increasing G is attributed by a transition from polycrystalline to either lower single crystal or grain boundary (i.e. bicrystal) fracture energies as the approximate constant (C) becomes significantly less than G as G increases. The transition between the two regimes is when C and G are similar. Extensive analysis of strength-grain size data, and more limited directly correlated fractographic data support the proposed model. Spontaneous cracking in non-cubic materials is shown to support the model, but not be an alternate explanation for the transitions seen in machined Al2O3 or BeO. This analysis also further supports the observation that machining flaws do not vary greatly with typical variations in machining parameters. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 28, 1979
- Accession Number
- ADA077536
Entities
People
- R. W. Rice
Organizations
- United States Naval Research Laboratory