Comparison of K_IC values for SiC whisker reinforced ceramic composites obtained by using various methods

The fracture toughness (K_IC) values determined by indentation microfracture method (IM) for SiC whisker reinforced Al₂O₃ and ZrO₂ based composites were calculated with different IM equations and compared with those obtained by single edge notched beam (SENB) technique. Experimental results show that the K_IC (IM) values calculated with different equations are quite different one from another. For composites without phase transformable components the K_IC (IM) and K_IC (SENB) values are practically on the same level, but for composites with phase transformable components (partially stabilized zirconia) the K_IC (SENB) values are always higher than K_IC (IM). This is because that the IM method can not reveal sensitively the toughening effect due to dynamic t-m transformation of ZrO₂ as the SENB method does. The accuracy of the IM method depends on the suitability of the IM equations and was evaluated for the materials used in this investigation. Two new IM equations are suggested with which the K_IC (IM) values can be obtained very close to K_IC (SENB) values for composites having phase transformable components.