Comparative study on indentation fracture toughness evaluations of soda-lime-silica glass

The fracture toughness of a commercial soda-lime-silica glass has been meas ured by the Vickers indentation method at four different indentation loads between 1.96 and 9.8 N and four different indentation times between 15 and 30 s. Indentation fracture toughness (IFT) values were calculated using 14 different formulae based on the Palmqvist crack model, the median crack mod el, and the curve fitting approach. An assessment of the compatibility of t he IFT values determined from identical measurements indicates that four fo rmulae based on the curve fitting approach and the Palmqvist crack model yi elded an IFT of 0.89 +/- 0.02 MPa m(1/2) at an indentation load of 1.96 N. A different set of formulae based on all types of approach yielded an IFT o f 1.00 +/- 0.02 MPa m(1/2) at an indentation load of 9.8 N. The calculated value of IFT for the soda-lime-silica glass at 1.96 N is in close agreement with its reported fracture toughness measured by the standard conventional test. Plots of the dimensionless fracture toughness parameter against crac k/indentation ratios did not reveal the nature of the cracks in the materia l. The influence of load on IFT is more significant than that of time. The observed variations in IFT with indentation load in the soda-lime-silica gl ass compared with similar variations for cr-silica carbide indicates that t he load dependence of IFT in brittle solids is governed by the degree of cr ystallinity of the material.