Torsion Load

The next six typical concepts will allow motion through an elastomer in three or more directions. First, Fig. 2.16 would be a typical design for seismic concerns and bridge-bearing pads. It is capable of supporting high compressive loads while allowing for soft lateral (shear) and torsional characteristics. Although the part shown is a circular unit, square and rectangular products are more common in the construction industry.

Fig. 2.17 shows another high shape factor design, which in this case takes the elastomer in compression (that is, radially), with the shear modes being axial and torsional.

Fig. 2.18 is similar to Fig. 2.17 except that its metal components have a spherical contour, allowing for torsion about the center line and radial axis. For each of these directions the radial-load deflection characteristic

Axial compression concept with two shear modes

Figure 2.17 Radial compression concept with two shear modes

F Radial

Figure 2.17 Radial compression concept with two shear modes

F Radial

is quite stiff. The axial characteristic is indeed stiffer than the shear in the previous configuration. The torsion about the axial axis is also similar, but the torsion about the radial axial axis is soft.

Figure 2.19 shows a product similar to one used in the rapid-transit and

Figure 2.18 Radial compression concept with three shear modes

Radial

Figure 2.18 Radial compression concept with three shear modes

Radial

p Radial

Axial compression with three shear modes

Axial compression with three shear modes

about the axial axis and torsion perpendicular to that axis. This configuration is a combinadon of Figs. 2.20 and 2.21.

For auxiliary generators and compressors any of these configurations would be viable. However, each individual applicadon has its own design requirements.

One of the parameters to consider when applying an elastic suspension system to an energy-producing device is the degree of motion that will be acceptable to the installation.

The performance of elastomers is of major interest and concern to the design engineer. The readily available data concern the tensile-elongation factor, the compression set, results from durometer tests, and information on oil resistance, heat aging, and the static modulus. In designing for a given environment, certain information makes the designer's job easier and the actual results closer to that predicted. These types of data are normally generated at the designer's facility with in-house-developed test equipment and procedures. They include: (1) dynamic modulus at various strains, frequencies, and temperatures; (2) ozone resistance at different concentration levels; (3) loss factor at various strains, frequencies, and temperatures; (4) fatigue of various shape factors and cyclic strains and temperatures; (5) effects of different ingredients such as carbon black; (6) drift and set characteristics at various initial strains and temperatures; and (7) electrical resistance.

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