Composite Effects on Tire Mechanics

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Composite Effects on Tire Mechanics

• MAE 537 Mechanics of Composites
• Paul Mayni
• May 2005

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Agenda

• Pneumatic tire evolution
• Effects of carcass and belt angles
• Ply steer phenomenon
• References

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Interesting Quotes

• The complexity of the structure and behavior of
  the tire are such that no complete and
  satisfactory theory has been propounded
• Temple, Mechanics of Pneumatic Tires

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Interesting Quotes

• Those of us who are active in research and
  development as applied to rubber-like materials
  are well aware of the truly interdisciplinary
  nature of tire-to-ground traction. Physics,
  chemistry, metallurgy, dynamics, tribology,
  thermodynamics, heat transfer elasticity,
  viscoelasticity, rheology, elastohydrodynamics,
  play complex and intertwined roles in determining
  the magnitude of the frictional coupling that
  ultimately exists in the contact patch
• D.F. Moore 1973 Symposium on The Physics of Tire
  Traction

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Pneumatic Tire Evolution

• First modern tire can be considered a simple
  ply construction
• From about 1920-1950 bias tires dominated the
  market

An even number of cross plies of approximately
/- 45 were used as shown in the figure
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Pneumatic Tire Evolution

• Resisting the radial movement in Europe, the
  belted bias tire was developed in North America

American tire manufactures hoped to avoid the
costly transition to radial tires Typical
construction consisted of additional belt layers
restricted to the tread summit and using the same
angles and materials as the carcass plies
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Agenda

• Pneumatic tire evolution
• Effects of carcass and belt angles
• Ply steer phenomenon
• References

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Bias vs. Bias-belted

• Unrestricted growth of a bias tire for various
  cross-ply angles is shown in Figure 5.8
• With the addition of belt layers of increased
  stiffness and cable material the shape of the
  inflated carcass changed as seen in Figure 5.9

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The Radial Tire

• Superior performance gains in comfort, wear, and
  handling were achieved with the introduction of
  the radial tire

In a radial tire the carcass plies are oriented
at 90, and the steel belt package acts to
distribute the tires load more efficiently and
maintain a particular summit profile
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Bias vs. Radial

• Within the contact patch, a bias tire will
  undergo extreme lateral deflection as shown in
  Figure 5.15.
• In contrast, the radial tire resists this
  tendency. This greatly reduces tire wear, heat
  generation, and provides responsive handling
  characteristics

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Bias vs. Radial

• The shape of the inflated tire is not a simple
  constant radius.
• Why is this important? If you can predict the
  inflated shape you can design the tire mold to
  have the ideal inflated shape thus reducing
  residual stress of the inflated tire.

This figure shows the effect of changing the
bias angle of a belt-less membrane
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Bias vs. Radial

• The addition of a belt package to a radial
  sidewall design adds additional complexity to the
  problem
• Two interesting behaviors have been observed
• For bias-belted tires there exists a special belt
  angle that in combination with the carcass angle
  generates a flat summit
• Radial tires without a belt package are unstable

Top View
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Bias vs. Radial

• An example of the flat angle solution is shown
  above
• Regardless of inflation pressure, there will be
  no tendency for the tire to become round. In
  other words the equilibrium shape is flat.

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Bias vs. Radial

• Consider a pure radial tire
• Remove the belts and inflate
• Note the characteristic round radial membrane
  shape
• Increase the pressure a little

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Bias vs. Radial
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Agenda

• Pneumatic tire evolution
• Effects of carcass and belt angles
• Ply steer phenomenon
• References

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Conicity Ply Steer

• Conicity is derived from imagining a tire
  constructed to take the shape of a truncated
  cone. Based on geometry this configuration would
  generate a force towards the apex of the cone
  regardless of the direction of rotation.

Ply steer can be determined from lateral force
variation measurements. An instrumented spindle
records lateral force of a tire. Forward and
reverse rotations are used in order to separate
ply steer from conicity. Ply steer, generated by
a coupling of bending and stretching, is
dependent on the tires rotational direction.
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Ply Steer

• The effects of stacking sequence of the tires
  summit plies directly influences the ply steer
  behavior

Example A in the figure graphically depicts the
results of an asymmetric stacking
sequence Example B has little or no coupling of
bending and stretching
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Ply Steer

• Typical tire constructions are shown in Figure
  8.2.78
• Resulting conicity and ply steer values are shown
  in Figure 8.2.80

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Ply Steer

• The ABD matrix relates membrane loads and moments
  to strains and curvature
• The B16 and B26 terms are dependent on the
  stacking sequence
• Table 3.10 shows the effect of stacking sequence
  on ply steer force

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Ply Steer

• For reference, some examples of ABD matrices for
  bias, belted-bias, and a radial tire are provided

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References

• Bogdanovich, A. E., Pastore, C. M., (1996).
  Mechanics of Textile and Laminated Composites.
  Chapman Hall, UK
• Haney, P., (2003). The Racing and
  High-Performance Tire. TV Motorsports,
  Springfield Illinois.
• Clark, S. K., (1981). Mechanics of Pneumatic
  Tires. US Department of Transportation,
  Washington, D. C.