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Research Papers

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

[+] Author and Article Information
Hironori Tohmyoh

Mem. ASME
Department of Finemechanics,
Tohoku University,
Aoba 6-6-01, Aramaki,
Aoba-ku, Sendai 980-8579, Japan
e-mail: tohmyoh@ism.mech.tohoku.ac.jp

Daiki Taniguchi

Department of Finemechanics,
Tohoku University,
Aoba 6-6-01, Aramaki,
Aoba-ku, Sendai 980-8579, Japan

Manuscript received November 22, 2018; final manuscript received February 19, 2019; published online April 1, 2019. Assoc. Editor: Seyed Allameh.

ASME J of Medical Diagnostics 2(3), 031001 (Apr 01, 2019) (7 pages) Paper No: JESMDT-18-1059; doi: 10.1115/1.4042926 History: Received November 22, 2018; Revised February 19, 2019

A bending test scheme for accurately determining the structural elasticity of human nails is reported. The structural elasticity expresses the deformability of a multilayered 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 the 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.

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Figures

Grahic Jump Location
Fig. 1

(a) Sample preparation procedure and (b) cross section through a nail

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Fig. 2

Schematic of the bending test for a curved beam

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Fig. 3

(a) Test platform and (b) typical structure of the force sensor. The sensor is comprised of a double-beam cantilever, a probe for applying the load, and a capacitance sensor. (c) Details of A in (a), where the load was applied to the outer surface of the nail toward the center of curvature.

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Fig. 4

Experimental results from human nail samples: (a) examples of P–δ relationships for samples without nail polish, (b) examples of P–δ relationships for samples with nail polish, and (c) the relationships between P R3 (θ0 − sinθ0 cosθ0)/(2 I) and δ. The slope of this relationship gives the value of SE in bending, (d) the values of SE of nail samples without nail polish, (e) the values of SE of nail samples with nail polish, and (f) comparison between the average values of SE between the samples without nail polish and those with nail polish.

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Fig. 5

(a) Example of the P–δ relationship of the nail polish sample and (b) the values of E of the nail polish samples

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Fig. 6

The values of SE and FR as functions of hnp/h

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Fig. 7

Experimental results for human hair samples: (a) A photograph of the experimental setup, where the load was applied in the direction of the long axis of the cross section through the sample, (b) examples of P–δ relationships for the human hair samples obtained with the load applied in two different directions, and (c) the relationships between P L3/(3 I) and δ. The slope of this relationship corresponds with SE in bending, (d) the values of SE of the hair samples, and (e) comparison of the average values of SE between the nail and hair samples.

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Fig. 8

Cross section through a hair

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