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Research Papers: Other (Seals, Manufacturing)

Composite Structure Design of O-Rings Using Material Behavior to Decrease Strain Energy and Permanent Deformation

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

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

J. Tribol 131(4), 042202 (Sep 24, 2009) (10 pages) doi:10.1115/1.3203147 History: Received December 30, 2008; Revised July 12, 2009; Published September 24, 2009

The performance of elastomeric seals degrades over time in use due to the development of permanent material deformation. The existence of localized high stress regions below seal-housing contact areas led to consideration of improving O-ring design by modifying material behavior to decrease strain energy, and so permanent deformation, in these regions. Photoelastic stress analysis was used to experimentally characterize the stress and strain fields in O-ring sections and to validate finite element models used in design studies. O-ring section designs that included small inset regions of different material behavior than the larger surrounding section were investigated with the intent of manipulating and reducing the strain energy content. Finite element models of O-rings were used to characterize the strain energy content and distribution for inset materials with various stress-strain behaviors. Measurements of permanent deformation and load-deflection behavior of specimens held under applied compression over time showed dependence of the amount of permanent deformation on strain energy. Design rules were extracted from results of studies in which inset region material stiffness, stress-strain behavior, size, and location in the larger section were varied. O-ring sections with regions of less stiff material result in lower strain energy and more uniform strain energy density distribution than the typical one-material seal. Inclusion of less stiff softening stress-strain behavior material insets in the larger O-ring section produced reduction in strain energy level and favorable redistribution of the high strain energy density regions compared with the conventional one-material one-material-behavior design. Similar concepts will apply to the design of other elastomeric structures in which permanent material deformation affects structure performance.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Photoelastic fringe pattern and (b) calculated principal stress difference contours for applied pressure loading of 19,800 Pa on the baseline O-ring section design

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Figure 2

Force required for 20% compression for specimens with different amounts of imposed radial compression

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Figure 3

Initial strain energy density, permanent deformation after 21 days, and decay rate of 20% compression force for specimens with varying initial radial compression

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Figure 4

(a) O-ring section model with inset regions of different mechanical properties in a larger surrounding section mounted in the photoelasticity test stand. (b) Fringe pattern for applied displacement loading of a specimen.

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Figure 5

Contact pressure distributions for various O-ring designs. (a) Base design of an elastic homogeneous 6 MPa modulus of elasticity material. (b), (c), and (d) Sections composed of a 6 MPa elastic modulus larger section with two 21.3 mm insets of different initial stiffnesses and different stress-strain behaviors.

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Figure 6

Typical contour plots of strain energy density, MJ/m3, and percentage of section area at various strain energy density levels for the baseline and modified seal section designs

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Figure 7

Strain energy content calculated using different numbers of strain energy density contours and maximum contact pressure (dashed line) for the section designs described in Table 4

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Figure 8

Strain energy density distributions, MJ/m3, for (a) the baseline design of an single elastic material, design number 23, (b) a single hardening material design, design number 11, and (c) Design with softening insets, design number 4

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