Effect of SiC addition on R-curve behaviour of alumina and ZTA ceramics

The fracture behaviour of alumina and ZTA ceramics containing 10 to 30wt% SiC particles was investigated during tests of controlled crack growth in three point bending of single-edge-notched samples. The crack was initiated and slowly grown by repeated loading and removing of the load. Crack length, c, was measured by in situ observation using a special video camera. The necessary force, P, responsible for a crack length increase was recorded by computer control of the Zwick testing machine. From a crack length, c, and force, P, the stress intensity factor, K-l, was calculated. The tests showed that SiC addition strongly decreases the effect of R-curve in alumina and ZTA ceramics. This phenomenon was explained by analysis of residual stress state in ceramics. An increase of resistance to crack initiation and resistance to fracture of the studied ceramics with increase of SiC addition was also found.