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I am currently reading “Fundamentals Of Vehicle Dynamics” by Thomas D. Gillespie.

enter image description here

The author states how tires generate the required frictional forces for movement by 2 methods :

1)Hysteresis 2)Adhesion

It’s a no-brainier in understanding how adhesion can help generate friction. What I don’t understand however is how Hysteresis can help produce the same ?

What is the mechanism using which tires generate forces by stretching and un-stretching ? How does this work?

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  • $\begingroup$ So what exactly does the author state - may help if you provide all the info so we can understand your homework... $\endgroup$
    – Solar Mike
    Jan 7 '18 at 14:58
  • $\begingroup$ Any feedback on the answer I gave to your other question ? As in this one : engineering.stackexchange.com/q/18759/10902 $\endgroup$
    – Solar Mike
    Jan 7 '18 at 14:59
  • $\begingroup$ @SolarMike I’m sorry but I don’t consider that an answer or an explanation. It does raises a nice question of how the asymmetry might depend upon the construction of the metal belts inside.But again, I doubt that it does as those belts are always symmetrical circumferentially. $\endgroup$
    – RedHelmet
    Jan 7 '18 at 15:13
  • $\begingroup$ @SolarMike the author just states what’s written in the photo I’ve posted in the question. He doesn’t go into explaining the mechanism any further. The topic ends quite abruptly as it began, leaving the reader wanting more. As for the homework I’ve done, I tried Google but in vain. There just isn’t any information on this topic there that I could find. So, I turned to StackExchange to see if I could get some wisdom on the same from the experts or otherwise. $\endgroup$
    – RedHelmet
    Jan 7 '18 at 15:19
  • $\begingroup$ So, the author has that photo with no supportng text in the chapter - why don’t I believe that? $\endgroup$
    – Solar Mike
    Jan 7 '18 at 16:46
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When you compress or stretch a material, the work done is partly converted into elastic energy, which causes the body to return (approximately) to it's initial length, once you remove the load. On the other hand, some of the energy is dissipated into heat. This is the primary cause for hysteresis. (Tyre-)rubber, due to it's visco-elastic properties is strongly affected by hysteresis, shown by the following stress-strain-diagram (force-extension-diagram, to be precise)

Fig 1 Source: https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/Elastic_Hysteresis.svg/930px-Elastic_Hysteresis.svg.png

This means if you apply a load to rubber and release it afterwards, you will measure a different force for the same deformation during load and release.

If you now consider a tyre on a flat surface, the contact surface between the two materials forms a plane, meaning that in the front of the contact surface (in the direction in which the tyre is rolling) the rubber is in a loading phase (blue curve). In the back of the contact surface the rubber is unloading (red curve). This results in a non-symmetrical stress-distribution, as shown in the following figure. (Albeit for both of the bodies being cylinders, but the principle is the same)

Fig 1 Source: https://upload.wikimedia.org/wikipedia/commons/8/8c/Pressure_distribution_for_viscoelastic_rolling_cylinders.png

This results in a counterclockwise moment, with respect to the axis of rotation (clockwise), in other word: a retarding moment, or rolling resistance.

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  • $\begingroup$ Consider the treads that are going to become the contact patch. Do these treads get stretched or squished ? I mean either way, how is the direction of the stresses developed in a direction normal to the ground ? $\endgroup$
    – RedHelmet
    Jan 9 '18 at 2:57
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I'm guessing that you are confusing the terms friction coupling with traction.

If I pull a trailer over a flat, level surface, most of the resistance is due to the hysteresis in the contact patch. The adhesion prevents the tire from deforming and then rebounding and recovering it's energy. Pulling a trailer across wet ice is easier than pulling it across sanded concrete. This is the coupling between deformation forces and the adhesion which fights against, say, lateral stretching and return of the squashed tire.

Basically, just realize that adhesion and deformation interact with each other and can't usefully be separated in the real world. They are strongly coupled.

The coupling also detracts from traction since some of the available adhesion is now expended on opposed forces caused by the deformation.

Here's a convenient PDF - see page# 3. Rolling Resistance

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  • $\begingroup$ That pdf really does give a huge detailed explanation of the phenomena involved : good one : that will give the OP some reading :) $\endgroup$
    – Solar Mike
    Jan 8 '18 at 22:23
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Here is my simple answer of how tires generate traction [frictional] forces for movement by Method/Process #1 in the diagram, Hysteresis:

  • Think of Hysteresis as the amount of 'deformation' a piece of rubber is capable of, rubber being an elastic/deformable material, and specifically tread rubber, when it comes in contact with the irregularities of a road surface, whether asphalt, new concrete, worn concrete.

High Hysteresis = High Amount of Tread Rubber Deformation/Soft Rubber Compound [think racing tires]; High Amount of Traction; but also a High Amount of Heat Generation [internal molecular friction, think of constantly bending a iron bar and the heat produced at the bend point]; and, a High Amount of Rolling Resistance [will use more fuel to overcome this traction process];

  • Drive Tire Acceleration Hysteresis Traction - all drive tires exhibit a certain amount of 'slip' when the torque of the engine is applied to them under acceleration. The tread rubber surface is deformed by the minute [extremely small] irregularities of the road surface. The rougher the surface, the more the tread rubber deformation, the more the traction, as the tread rubber 'sinks' into the deformation.

  • Non-Drive/Trailer and Steer Tire Braking Traction - see above, but in reverse. When the brakes are applied, the deformation the tread rubber is undergoing creates a traction/braking force.

Trust this helps.

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Hysteresis essentially implies the loss of energy in an activity of cyclic nature.Here in case of motion of tire the portion of tread in contact with road surface is under compression due to load of the vehicle and as it moves on it gets extensional deformation. The compressed tread rubber will try to come back to its original state due to its elastic part of viscoelastic rubber. The viscous part gets converted to heat thereby heating the tread compound.This heat generation is considered as consequence of some form of friction named as hysteresis friction component, being different from the normal frictional heat. Dr. B R Gupta, Retd. Prof. I I T Kharagpur, India

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