9412691 Shetty Toughened ceramics, including transformation-toughened zirconia based ceramics and whisker-and fiber-reinforced ceramic composites, are susceptible to true cyclic fatigue phenomena. The associated high subcritical crack-growth rates in cyclic loading can arise from either extrinsic (degradation of crack shielding) or intrinsic (crack-tip damage) mechanisms. The research proposed will investigate the origins of cyclic fatigue in ceria partially stabilized zirconia/alumina and self-reinforced silicon nitride by separating the contributions of the extrinsic and the intrinsic mechanisms via direct measurements of crack shielding using Roman microprobe spectroscopy. Critical comparison of the measured shielding with the theories of crack shielding and direct examination of the transformation or bridging zones via Transmission and scanning electron microscopes techniques are also the important elements of the proposed research. %%% The proposed research will investigate the origin of cyclic fatigue in ceria-partially stabilized zirconia/alumina and self reinforced silicon nitride by means of Roman spectroscopy and electron microscope. ***
