Characterization of Mechanical Damage Mechanisms in Ceramic Composite Materials.
Technical rept. 24 May 85-23 May 86,
SOUTHWEST RESEARCH INST SAN ANTONIO TX
Pagination or Media Count:
Yielding behavior and deformation modes are characterized for single crystal and polycrystalline yttria-stabilized ZrO2 tested in compression from 23C to 800C. The plastic flow of single crystal specimens is orientation and temperature dependent, and is interpreted in terms of TEM evidence of dislocation activity, and an hypothesized tetragonal-to-cubic transformation. Polycrystalline material deforms at intermediate temperatures about 800C by forming unstable shear bands, which flow via grain boundary sliding and cavitation. Although both strength and ductility increase with strain rate, polycrystalline strength decreases rapidly with increasing temperature. Continuous SiC fiber-reinforced glass matrix composites have been tested in compression over a wide range in temperature and loading rate. Both uniaxial and crossplied fiber orientations were studied. Strength is found to depend sensitively on orientation and loading rate, while temperatures to 800C have less effect. Orientation effects are explained in terms of matrix microfracture and fiber buckling. The latter are shown to also control strengthening at very highHopkinson Pressure Bar strain rates, where it is hypothesized that strength is enhanced by inertial effects which inhibit the development of the localized pockets of intense matrix microfracture and general buckling required for the nucleation of fiber kinks.
- Ceramics, Refractories and Glass