Analysis of Stress Intensity Factor of Chevron Notched Specimen and Measurement of Fracture Toughness of Ceramics

摘要

The stress intensity factor of a chevron notched bend specimen was analysed by using three dimensional BEM and the results were compared with those obtained by using Bluhm's slice model. The stress intensity factor was evaluated in two ways as a function of crack length; one is the average value of maximum stress intensity factor and minimum one at crack front, and the other is the average one obtained by energy approach. Those average stress intensity factors evaluated by BEM and slice model show good agreements. The distribution of stress intensity factor along crack front was also evaluated for several crack lengths. Four point bending test using the chevron notched Si_3N_4 specimens was further conducted and the fracture toughness was evaluated using the average stress intensity factor mentioned above. This fracture toughness was compared with that measured by Indentation Microfracture Method. As a result, when the chevron notched specimen fractured stably, a good agreement was shown between the measured values of fracture toughness by two methods. On the other hand, when unstable fracture occurred in the chevron notched specimen, the fracture toughness by the chevron notched specimen is more than 100 percent larger than that by Indentation Microfracture Method.