Comparative study of micro-indentation and Chevron notch fracture toughness measurements of silicate and phosphate glasses

Although fracture toughness (KIc) studies of glass and ceramics typically utilize the Chevron notch technique, this method requires considerable time for sample preparation. On the other hand, sample preparation for the indentation fracture toughness (IFT) method requires only a quick polish of the surface, thereby saving considerable time. In order to compare the more rapid indentation methods with Chevron notch values, IFT measurements were made on a series of 15 silicate and phosphate optical and laser Schott catalog glasses. IFT values were determined using the Niihara et al. and Anstis et al. formulations. The 2-σ difference between the Niihara et al. IFT formulation and Chevron notch values was 0.21 MPa m1/2 and showed no systematic difference. However, IFT values obtained using the Anstis et al. formulation showed a systematic deviation from Chevron notch values with IFT values underestimating Chevron notch data by up to a factor of two. IFT values calculated with the Niihara et al. equation provide a quick and generally reliable guide to fracture toughness values of oxide glasses.