Research Papers: Other (Seals, Manufacturing)

Improving the Long-Term Performance of Elastomeric Seals by Material Behavior Design

[+] Author and Article Information
Ryan B. Sefkow, Nicholas J. Maciejewski, Barney E. Klamecki

Department of Mechanical Engineering, University of Minnesota—Twin Cities, Minneapolis, MN 55455

J. Tribol 131(4), 042203 (Sep 24, 2009) (9 pages) doi:10.1115/1.3203148 History: Received December 30, 2008; Revised July 12, 2009; Published September 24, 2009

Previously it was shown that including smaller inset regions of less stiff material in the larger O-ring section at locations of high stress results in lower strain energy density in the section. This lower energy content is expected to lead to improved long-term seal performance due to less permanent material deformation and so less loss of seal-housing contact pressure. The shape of the inset region, the time-dependent change in material properties, and hence change in seal behavior over time in use were not considered. In this research experimental and numerical simulation studies were conducted to characterize the time-dependent performance of O-ring section designs with small inset regions of different mechanical behaviors than the larger surrounding section. Seal performance in terms of the rate of loss of contact pressure of modified designs and a baseline elastic, one-material design was calculated in finite element models using experimentally measured time-dependent material behavior. The elastic strain energy fields in O-ring sections were calculated under applied pressure and applied displacement loadings. The highest stress, strain, and strain energy regions in O-rings are near seal-gland surface contacts with significantly lower stress in regions of applied pressure. If the size of the modified region of the seal is comparable to the size of the highest energy density region, the shape of the inset is not a major factor in determining overall seal section behavior. The rate of loss of seal-housing contact pressure over time was less for the modified design O-ring sections compared with the baseline seal design. The time-dependent performance of elastomeric seals can be improved by designing seals based on variation of mechanical behavior of the seal over the seal section. Improvement in retention of sealing contact pressure is expected for seal designs with less stiff material in regions of high strain energy density.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Strain energy density in radially compressed specimens, measured permanent deformation on release of restrain after 21 days, and rate of change over 21 days of force needed to diametrically compress constrained specimens by 20%

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Figure 2

Elastic strain energy density (MJ/m3), percentage of the section area with different strain energy density levels, and maximum contact pressure for (a) conventional one-material design O-ring. (b) O-ring section composed of a large section with the same properties as in Fig. 1 containing initially circular inset regions of less stiff material.

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Figure 3

(a) Photoelastic test stand. (b) Applied pressure loading apparatus.

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Figure 4

Results from photoelastic and finite element analyses for applied pressure loading of 19,800 Pa. ((a) and (b)) Photoelasticity fringe pattern and calculated principal stress difference contours for a one-material, baseline section design. ((c) and (d)) Fringe patterns for O-ring sections with an inset of elastic modulus E=2 MPa material near the top surface and near the bottom surface of a surrounding section of E=3 MPa.

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Figure 5

Inset shapes used in studies of effects of shape on strain energy density

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Figure 6

Elastic strain energy density (MJ/m3) contour plots for (a) single material section, and ((b)–(d)) sections with circular, horizontal oval, and arc-shaped insets

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Figure 7

Measured contact force over time for Buna-N O-ring and polyurethane specimens subjected to fixed displacements

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Figure 8

Maximum contact pressure versus time for Buna-N and polyurethane baseline and modified designs subjected to imposed displacement

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Figure 9

Rate of change in maximum contact pressure for baseline and modified section designs under imposed displacement loading

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Figure 10

Contact pressure retention over time for baseline and modified designs of polyurethane seal




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