Statistical characterization of the mechanical properties of glass ceramics for structural applications

Glass-ceramics (GC) are mostly produced in two steps. First, a glass is formed by a glass manufacturing process; then, the glass is cooled down and further reheated in a second step. In this heat treatment the glass partly crystallizes. GC share many properties with both glasses and ceramics, but the measured fracture toughness of GC is usually one order of magnitude higher than that of glass. This is probably due to the material underlying microstructure, because the crystallized phases in GC coagulate into grains within the amorphous matrix so that, while a crack opens, the grains can bridge its lips [1]. Here, we report the results of an experimental campaign directed towards structural applications, aiming at the characterization of the bending strength of glass ceramics. The considered tests were: (a) biaxial bending on square 100 mm × 100 mm specimens under concentric rings (r1= 45 mm, r2 =9 mm) according to UNI-EN 1288-5; (b) 4-point bending tests on 1000 mm × 360 mm specimens, according to UNI-EN 1288-5. Both 6 mm and 8 mm thick plies were tested: each sample was composed of 50 specimens for test type (a) and 20 specimens for test type (b), for a total number of 140 specimens. We find that the probability distribution by Weibull is able to accurately represent the experimental data. The corresponding Weibull parameters are similar for both type (a) and type (b) tests, and for both the thicknesses. We find that the statistical distribution of the tensile strength for glass-ceramics has a much lower dispersion than that of glass. This property, together with the higher fracture toughness, renders glass ceramic more performant than glass for what structural applications is concerned.