Influence of material properties and fingertip size on the power-law equation for soft fingers

In this paper, we investigate the influence of size and material properties of fingertips on the power-law equation for soft-finger contacts. Fingertips made of different materials of various sizes were tested, and the parametric relationship between normal forces and radii of contact was found. The experimental results validate that the growth of contact radius, a, is a function of the normal force, N, according to the power law, that is, a = c N^γ, for nonlinear elastic soft fingers with large deformation. The experimental results suggest that γ is a material-dependent constant, decreasing with the hardness of the soft-finger materials and ranges from 0 to 1/3. In addition to material properties, the constant c is dependent upon the size and geometry. Overall, the constant c increases as the soft finger becomes softer and larger, and decreases when the soft finger becomes harder and smaller. An INSTRON Model 1011 equipment was employed to conduct the experiments with different fingertip materials, loading rates, and ranges of normal force.