Fracture resistance evaluation of ceramic matrix composites

The fracture resistance of CMCs has been discussed. The effects of specimen size on fracture behavior using compact tension test specimens were investigated. Unloading-reloading sequences were used to measure the effective crack length of test specimens. The effects of the magnitude of unloading on the fracture behavior of test specimens were also investigated. 50% and 100% of unloading resulted in severe damage on the fracture surfaces of reinforcing fiber because of interfacial wear between fiber and matrix. Therefore, it was found that it is better to reduce the amount of unloading in order to reduce frictional damage on the reinforcing fibers. The crack-initiation fracture resistance of SiC fiber reinforced SiC matrix composites (SiC/SiC) and carbon fiber reinforced carbon matrix composite (C/C) were affected by test specimen size. These size effects are gradually decreased with increasing of test specimen size.