Determination of the Structural Elasticity of Human Fingernails by Bending Test and Comparison with the Structural Elasticity of Human Hair

Abstract

A bending test scheme for accurately determining the structural elasticity of human nails is reported. The structural elasticity expresses the deformability of a multi-layered material for bending, and it is the flexural rigidity without depending on the external dimensions. The human nail samples used in this study were prepared from the free ends of the nails and are, therefore, curved, so the equation to determine the structural elasticity was derived from elastic, curved beam theory. The structural elasticity of the nail samples determined by the bending tests was found to be 2.19 GPa, and this value decreased by about 50% when nail polish was put on the nails. Lower value of Young's modulus of the nail polish was found to cause decrease in the structural elasticity of the sample. Moreover, we also measured the structural elasticity of samples of hair prepared from the same person by the bending tests. Surprisingly, the structural elasticity of the hair (4.37 GPa) was found to be twice that of the nails.