Thomas B. Troczynski

Application of The Potential Drop Technique to the Fracture Mechanics of Ceramics

An Electrical Potential Drop (PD) technique is used to follow crack growth in chevron-notched, four-point bend fracture toughness specimens of conductive ceramics. The potential drop in the vicinity of the notch was successfully modelled and the resulting routine was verified at room temperature using graphite as a model material and was applied at high temperatures to zirconium oxide ceramics. The resistance to brittle fracture of partially stabilised zirconia doped with 8 wt% Y2O3 decreased to ~3J/m2 at 1100°C and ~1J/m2 at 1300°C. Dispersion of s-Al2O3 particles in the PSZ matrix enhanced the overall resistance to fracture of the composite to a maximum of 1800J/m2 at 1300°C.

Loading-Unloading Techniques for Determining Fracture Parameters of Brittle Materials Utilizing Four-Point Bend, Chevron-Notched Specimens

A technique is described for determining the threshold stress intensity factor Kt at which a stationary crack just begins to move. If the crack velocity is described by v ~ KN, Kt can be measured via repeated cyclic loading stable-fracture unloading (UN) experiments. The resistance to fracture calculated for each cycle approaches the threshold (or initiation) value as the full fracture of four-point bend, chevron-notched specimens is approached. The experimentally measured resistance-to-fracture-initiation values for SiC was ~ 6J/m2, 30J/m2 for yttria partially stabilised zirconia, ~ 10 J/m2 for yttria fully stabilised zirconia, and ~ 80J/m2 for graphite. The R-curve behaviour of a PSZ- s Al2O3 composite was analysed by the UN technique. The nonelastic energy dissipation rate for this composite approached 600J/m2.

The role of potassium ions in the degradation of sodium β/β″-alumina

Abstract Fracture mechanics and radiographic experiments were undertaken to determine the role of K + impurity in electrolyte degradation during Na + electrolysis through Na β/β″ -Al 2 O 3 . The results indicate that potassium ions enhance the degradation. Radiographic results indicate that for current densities of ∽ 1 A cm −2 , K + is reduced and precipitates in the ceramic microstructure. Spontaneous fracture of samples during electrolysis at high current densities was observed.