Table 2.

Summary of the structure–property relationships of the woodpeckers' beaks, including area fraction, mechanical properties, aggregate modulus/hardness and moment of inertia at each location along the beak.

distance from the tipcross-sectional shapearea (mm2)rhamphotheca (outer layer)foam (middle layer)
area fraction (%)area (mm2)hardness (MPa)modulus (GPa)area fraction (%)area (mm2)hardness (MPa)modulus (GPa)
10.4795.50.4457.5 ± 38.19.4 ± 0.40.00.0
2V12.472.99.0470.2 ± 68.99.9 ± 1.03.90.4262.2 ± 12.16.4 ± 1.9
3U27.146.512.6396.4 ± 34.38.4 ± 0.44.81.3215.6 ± 76.07.1 ± 4.8
4( )24.537.99.3284.0 ± 27.87.3 ± 0.56.01.5234.9 ± 12.36.1 ± 1.6
distance from the tipbone (inner layer)aggregate hardness (MPa)aggregate modulus (GPa)moment of inertia (mm4)flexural stiffness (GPa mm4) 
area fraction (bone) (%)area fraction (void) (%)area (mm2)hardness (MPa)modulus (GPa)
10.04.50.0436.9 ± 36.49.0 ± 0.40.00.18 ± 0.01
27.116.12.91219.6 ± 298.529.2 ± 5.1439.6 ± 71.99.5 ± 1.27.066.3 ± 8.3
328.520.213.21111.5 ± 128.029.0 ± 2.0511.4 ± 56.112.5 ± 1.042.0527.2 ± 40.9
440.515.613.71135.0 ± 82.232.3 ± 2.5581.4 ± 44.516.2 ± 1.321.6350.2 ± 27.9