Effect of microcracking on the fracture toughness and fracture surface fractal dimension of lithia-based glass-ceramics

The effect of thermally induced microcracks on the fracture toughness and fractal dimension of fully crystalline lithia disilicate glass-ceramics was studied. The fracture toughness, K sub IC , for the nonmicrocracked lithia disilicate, 3.02plus /minus0.12 MPam exp 1/2 , was significantly greater than the value of 1.31plus/minus0.05 MPam exp 1/2 for the microcracked specimens. The fractal dimensional increment, D exp * , was 0.24plus /minus0.01 for nonmicrocracked lithia disilicate specimens compared with a value of 0.18plus/minus0.01 for the microcracked specimens. The relationship between K sub IC and D exp * implies that the two materials exhibit dissimilar fracture behavior because of microstructural differences. Estimates of the characteristic length involved in the fracture process, alpha sub 0 , indicate that the materials have an identical fracture process at the atomic level. This apparent contradiction may be explained by the scale on which the measurements were taken. It is suggested that fractal analysis at the atomic level would yield equivalent D exp * values for the two different microstructures.