40 HARDNESS AND FRACTURE TOUGHNESS OF ALUMINA CERAMICS TVRDOĆA I LOMNA ŽILAVOST ALUMINIJ OKSIDNE KERAMIKE Lidija Ćurković, Vera Rede, Krešimir Grilec, Alen Mulabdić Faculty of Mechanical Engineering and Naval Architecture, Ivana Lučića 1, Zagreb, Croatia Izvorni znanstveni rad / Original scientific paper Abstract: Many methods are currently used to measure fracture toughness of ceramic materials. Methods based on crack-length measurements of cracks introduced into the sample surface by the Vicker's indentor have the advantage that they are easy to use, but they are very unreliable due to subcritical crack growth and the difficulty in determining the exact length of the cracks. The aim of the present work is to investigate the hardness from Vickers indentations and the fracture toughness based on crack-length measurements of cracks introduced into the sample surface of cold isostatically pressed (CIP)-Al 2 O 3 with 99.8 % purity. Key words: alumina ceramics, hardness, fracture toughness Sažetak: Puno metoda je u uporabi za određivanje lomne žilavosti keramičkih materijala. Metode bazirane na mjerenju duljina pukotina na površini uzorka nastalih Vikersovim indentorom mogu se lako primjeniti, ali su vrlo nepouzdane obzirom na podkritičan rast pukotine i teško određivanje točne duljine pukotina. Svrha ovog rada je ispitivanje tvrdoće Vikersovim indentorom i lomne žilavosti bazirane na mjerenju duljine pukotina na površini uzorka visoko čiste alumij oksidne keramike oblikovane hladnim izostatičkim prešanjem. Ključne riječi: aluminij oksidna keramika, tvrdoća, lomna žilavost