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 thr ee point bending tests of single-edge-notched samples. The crack was initia ted and slowly grown by repeated loading and removing of the load. The crac k length, c, was measured by in-situ observation using a special video came ra. The necessary force, P, responsible for a crack length increase was rec orded by computer control of the testing machine. From the crack length, c, and the applied force, P, the stress intensity factor, K-1, 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 t he residual stress state in the ceramics. An increased resistance to crack initiation as well as to fracture with increase of SiC addition was also fo und for the studied ceramics. (C) 2000 Elsevier Science Ltd. All rights res erved.