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Three-Dimensional Finite Element Simulations of the Dynamic Response of a Fingertip to Vibration

[+] Author and Article Information
John Z. Wu1

 National Institute for Occupational Safety & Health, Morgantown, WV 26505jwu@cdc.gov

Kristine Krajnak, Daniel E. Welcome, Ren G. Dong

 National Institute for Occupational Safety & Health, Morgantown, WV 26505

1

Corresponding author.

J Biomech Eng 130(5), 054501 (Jul 14, 2008) (8 pages) doi:10.1115/1.2947199 History: Received February 28, 2006; Revised May 19, 2008; Published July 14, 2008

Although excessive dynamic deformation of the soft tissues in the fingertip under vibration loading is thought to induce hand-arm vibration syndrome, the in vivo distributions of the dynamic stress/strain of the tissues in the fingertip under vibration conditions have not been studied because they cannot be measured experimentally. In the present study, we analyzed the dynamic responses of a fingertip to vibrations by extending our previously proposed three-dimensional finite element (FE) model. The FE model of the fingertip contains the essential anatomical structures of a finger, such as skin layers (dermis and epidermis), subcutaneous tissue, bone, and nail. Our analysis indicated that the fingertip has a major local resonance around 100Hz and that the vibration displacement in the soft tissues under the nail bed is less than 10% of those in the finger pad for all precompression levels and vibration range. The resonant frequency of the fingertip was found to increase from 88Hzto125Hz with the static precompression increasing from 0.5mmto2.0mm. These results suggest that structural and functional changes in vascular function will likely initiate from the fingerpad, the location that undergoes the greatest deformation during vibration exposure. The current predictions are qualitatively consistent with the physiological data collected from workers with vibration white finger.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

3D FE fingertip model. (a) External view. (b) Longitudinal cross section. ((c)–(e)) Cross Sections I–III, respectively, as labeled in (a). (f) Substructures of the model. The fingertip model is symmetric, and is composed of bone, nail, subcutaneous tissue, and outer and inner skin layers. The fingertip section is assumed to have a width of 20mm, a height of 18mm, and a length of 25mm.

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Figure 2

FE modeling of the fingertip in contact with a flat surface. (a) Side view. (b) Perspective view. The fingertip is in contact with a flat plate with a contact angle of 20deg.

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Figure 3

The distributions of the vibration displacement (U, mm) in the longitudinal section for six different vibration frequencies (f=16Hz, 32Hz, 63Hz, 125Hz, 250Hz, and 500Hz). The fingertip is precompressed by 1.0mm before being subjected to harmonic vibrations (magnitude of 0.5mm). I-I indicates the cross-sectional cut for the results shown in Fig. 4.

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Figure 4

The distributions of the vibration displacement (U, mm) in the cross section for six different vibration frequencies (f=16Hz, 32Hz, 63Hz, 125Hz, 250Hz, and 500Hz). The fingertip is precompressed by 1.0mm before being subjected to harmonic vibrations (magnitude of 0.5mm). The cross-sectional cut is at the center of the contact, as shown in Fig. 3.

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Figure 5

The distributions of the vibration displacement (U, mm) in the longitudinal section for six different vibration frequencies (f=16Hz, 32Hz, 63Hz, 125Hz, 250Hz, and 500Hz). The fingertip is pre-compressed by 0.5mm before being subjected to harmonic vibrations (magnitude of 0.5mm).

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Figure 6

The distributions of the vibration displacement (U, mm) in the longitudinal section for six different vibration frequencies (f=16Hz, 32Hz, 63Hz, 125Hz, 250Hz, and 500Hz). The fingertip is precompressed by 2.0mm before being subjected to harmonic vibrations (magnitude of 0.5mm).

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Figure 7

The distributions of the vibration displacement (U, mm) in the longitudinal section around the resonant frequencies at the soft tissues of the fingertip. Before being subjected to harmonic vibrations, the fingertip is precompressed to four different precompression levels, i.e., d0=0.5mm, 1.0mm, 1.5mm, and 2.0mm, as shown in (a), (b), (c), and (d), respectively. The resonant frequency of the soft tissues of the fingertip increases with increasing precompression.

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