Reliability of the chevron-notch technique for fracture toughness determination in glass

The applicability of the chevron-notch (CN) three-point bending test for determining the fracture toughness (KIc) of borosilicate glass was studied. As-received specimens with straight sharp notch were also tested in three-point bending for comparison purposes. It was found that both chevron and straight notched specimen geometries were equally suitable for the determination of fracture toughness in terms of average values and data variability according to Weibull and Studentʹs t-statistics. Further testing with CN geometry showed that annealing of specimens at a temperature (550 °C) higher than the glass transformation temperature led to a lower value of KIc. The difference in mean fracture toughness values (0.75 and 0.64 MPam1/2 before and after annealing, respectively), was ascribed to the different level of compressive residual stresses in the samples. The Studentʹs t-test was applied to confirm the statistical significance of the different KIc values measured. These results demonstrate that the CN technique is well-suited for reproducible and accurate determination of KIc values in glass.