Figure 3. Critical load for first damage as function of layer thickness d, for ceramic/polycarbonate bilayers indented with WC spheres. (a) Results for zirconia, alumina, and porcelain specimens, fixed sphere radius r = 3.96 mm. Filled symbols are PR data (R), unfilled symbols are PC data (C) or PY data (Y). Minimum n = 5 indentations each data point, standard deviation limits shown (some less than the size of the symbol). Solid lines are theoretical first-damage predictions for radial and cone cracking or quasi-plasticity. (Regression fits not shown.) (b) Predictions from Eq. 4 for hypothetical Dicor/polycarbonate bilayers, sphere radii r = 4 mm and 2 mm. Inclined lines—radial cracking (R); horizontal lines—cone cracking (C) or quasi-plasticity (Y). Shaded line represents a nominal occlusal load of 100 N, dashed vertical line indicates the corresponding thickness (
0.3 mm) at which this load will induce flexural radial cracking.
