The mechanical deformation of a human fingertip pressed on a flat plate was numerically analyzed using a three-dimensional human fingertip model based on CT images of a human index finger. The fingertip model consisted of three components: the distal phalanx, the nail, and the soft tissue composed of skin and subcutaneous tissue. The analyses were performed for seven different values of Young's moduli in the range 34 to 200 kPa, and for five different values of Poisson's ratios in the range 0.3 to 0.5. The numerical results obtained were compared with reported experimental data for a human fingertip. The numerical results showed that the deformation around the nail and the distal fingertip was generated subsequent to the generation of a large deformation of the pulp. The numerical deformation results showed a similar pattern as the experimental data. Using the numerical results, we calculated the length of the contact area from the lateral view and the width of the contact area from the axial view in order to qualitatively estimate the deformation. By comparing the numerical and experimental results, we found that there were no unique values of Young's modulus and Poisson's ratio for expressing the experimental results. These results suggest that the epidermal, the dermal, and the fat tissue constituting the soft tissue may influence the mechanical deformation by different amounts.

Nail strain due to compressive force in the finger pulp was different between the rectangular axes, between the distal and the proximal parts of the nail, and between the radial and the ulnar sides.

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