ACOUSTIC EMISSION BEHAVIOUR IN THE FRACTURE PROCESS AND STRENGTH DEGRADATION FOR THERMAL DAMAGED CERAMICS
Zhang Qingchun Lin Suzhen(Shanghai Institute of Ceramics,Academia Sinica)
Residual strength σ_R and residual fracture work γ_t as functions of temperature difference of thermal shock ΔT for two types of mullite-corundum ceramics, MA-3 and MA-6, are measured so that critical temperature difference ΔT_c is obtained,showing the thermal damage resistance of material. The technique of acoustic emission has been employed in the SENB bending test for the thermal damaged materials. As a general rule, the more acoustic emission counts, the more serious the damage of thermal shock.Change of the threshold value K_(IO) for the prime acoustic emission response, associated with the onset of crack propagation, and change of K_(Ic) for these ceramics, heattreated under the condition of ΔT≤ΔT_o are negligible. Further,threshold value K_(IO) decreases with the increase of ΔT. When ΔT≥600℃, the acoustic emission responds signally once the load is applied, the accumulative energy counts of acoustic emission increase with the increase of ΔT, and K_(Io) values decrease consequently ΔT≥1000℃, K_(Io) for both MA-3 and MA-6 ceramics increase somewhat. It is why the dissipation of partial energy by virtue of viscous glase phase contained in ceramics renders a moderate influence on the tendency of thermal damage.