Fracture analysis of mullite ceramics using acoustic emission technique

The detection of the micro-crack initiation and extension is necessary for the analysis of fracture mechanism of ceramics. Acoustic emission (AE) tcchnique was applied to detect the micro-crack initiation and extension in mullite ceramics during mechanical tests. The crack extension from natural defects prior to final failure was detected clearly during 4-point bending. The discrimination between the AE signal and noise, and the 2-channel locational detection can be achieved with the direct observation of AE waveforms. The crack extension behavior was also observed using chevron-notched beam bending tests with 2-channel AE measurements. To measure the transition point from stable to unstable crack growth, it is necessary to detect the correct fracture toughness of the chevron notch test. Cumulative AE energy showed a qualitative agreement with the crack velocity calculated from the change in crack opening displacement. The AE measurement can be used for the K Ic evaluation