Micro-scale damage characterization in porous ceramics by an acoustic emission technique

The fracture mechanism of porous silicon carbide (SiC) was investigated by using the acoustic emission (AE) technique. Four point bending tests were conducted at different loading speeds, and integrated with AE monitoring. The results revealed that the quasi-static fatigue behavior had a critical role on the degradation of fracture strength, and fracture was caused by the microcracks of binder. For the AEs detected during the bending tests, source wave analysis of AE was carried out in order to quantitatively estimate the volume of microcrack. It was found that the crack volume was slightly smaller than that of binder fracture observed by a scanning electron microscope (SEM), thus suggested that the small crack propagates in the binder and produces AEs. It was also found that the longer the testing time, the smaller the microcrack occurred at the lower stress level. Therefore, the fracture mechanism of the porous SiC was found to be controlled by particle binder fracture, which is time dependent. In addition, AE is testified as a useful technique to monitor the small crack of binder, which plays a very important role in material strength and filtering function of porous SiC.