Figure 8.

(a) The gross contact area, A_g, as a function of the compressive force for orientations of the finger pad of 30° (blue diamonds) and 45° (red circles); the data are taken from figure 5. The upper (blue) and lower (red) lines are for the 30° and 45° orientations, respectively, and represent best fits to equation (4.9) using the corresponding values of R_g (table 2) and values of β of 1.35 and 1.53 N⁻¹ (which are the best-fit values obtained for a compressive velocity of 2 mm s⁻¹). The fitted values of the Young's modulus, E_{0 g} (±1 s.e.) are 28.6 ± 0.3 kPa and 27.7 ± 0.5 kPa for the 30° and 45° orientations, respectively (assuming ν_g = 0.5). (b) The fingerprint ridge contact area, A_r, as a function of the compressive force; the data are taken from figure 5. The upper (blue) and lower (red) dashed lines for 30° and 45° orientations, respectively, are best fits to equation (4.10) using the same values of β and E_{0 g} used for (a). The fitted values of E_r (±1 s.e.) are 108 ± 11 and 134 ± 12 kPa, assuming that s = 1.33 and ν_r = 0.3. (Online version in colour.)