VISCOELASTIC EFFECTS IN TESTING OF AN AL2O3 CERAMIC CONTAINING A GLASSY PHASE

An alumina with 3 wt% glassy phase was tested at different loading rat es at two temperatures (900 and 1000-degrees-C). It was found that an increase in fracture toughness was accompanied by a decrease of the be nding strength at the same loading rates. A model is given, which desc ribes the experimental results by linear viscoelasticity of the second phase. Whereas the bulk properties are mainly due to the alumina grai ns and, therefore, remain nearly unchanged, the crack growth and the f racture behaviour in the intergranular regions is dominated by the vis cosity of the glassy phase. This leads to a non-unique value of K(lc), which is dependent on the temperature and the loading rate.