Toughness-curve behaviour of alumina-SiC and ZTA-SiC composites

The fracture behaviour of alumina and ZTA matrix ceramics containing 10–30 wt% SiC particles was investigated during controlled crack growth using three point bending tests of single-edge-notched samples. The crack was initiated and slowly grown by repeated loading and removing of the load. The 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 testing machine. From the crack length, c, and the applied force, P, the stress intensity factor, KI, was calculated. The tests showed that SiC addition strongly decreases the R-curve effect in alumina and ZTA ceramics. This phenomenon was explained by analysis of the residual stress state in the ceramics. An increased resistance to crack initiation as well as to fracture with increase of SiC addition was also found for the studied ceramics.