tire vertical load for torsional rigidty calculation

[moahmed]

hi guys, i was wondering about what load should i apply to the front tire to calculate the torque required for getting the torsional rigidity
i mean after my team have finsihed the dynamic simulation for the vehicle i got confused a little bit ,should i take the weight of the front tire and use it or use the results of the simulation .."what should be taken into account static force or dynamic force"


thanks for help


Mohamed Ashraf member at HFS racing team
Frame group
Helwan university

[nowhere fast]

Your question is pretty vague. What do you mean by ‘torsional rigidity’ and why do you need to calculate it? This will determine the accuracy you need and the items to consider.

I’m assuming that you are talking about torsional stiffness of your chassis here. Torsional stiffness is a rate relating angular deflection to the applied torsional load; if you perform a linear calculation then the stiffness will be the same no matter what load you pick as an increase in load will give a proportional increase in deflection.

[moahmed]

i know that there is a big difference between torsional rigidity and torsional stiffness ,torsional rigidity can be defined as the resistance of material to deformation (torsional rigidity=GJ) while torsional stiffness as you said before. in SAE papers ( design,analysis and testing of a formula SAE car chassis) these two terms are treated as one thing
speaking of the load required for calculating the torsional stiffness on what basis do i pick up my load ??

[Jay Lawrence]

Stiffness and rigidity are the same thing when talking about a structure. If you are talking about a material, then it doesn't really have a rigidity value, but does have a stiffness value (modulus of elasticity).

In the case of your chassis, if you believe they are different, what are the units of each?

[moahmed]

torsional stiffness "kt=T/theta" unit:Nm/rad
torsional rigidity=GJ unit:Nm^2

[Zac C]

torsional stiffness "kt=T/theta" unit:Nm/rad
torsional rigidity=GJ unit:Nm^2

and if you actually understood the practical application of theory you would realize that T/theta = kt = JG/L. You are going down a rabbit hole of non-value added analysis.

you need to stop worrying about semantics and start thinking about how to logically setup an engineering problem. Calculating, measuring, or modeling some kind of a metric is meaningless without some kind of idea of how that result is useful. and once you have that understanding the problem (usually) becomes straight-forward.

Here's a partial list of questions you need to answer for yourself:

Why do I need a calculation of torsional stiffness?

How stiff is stiff enough?

How can I setup an FEA simulation that is both meaningful to real world operating conditions and can be easily verified in the lab?

Is my system linear? and if it is linear what does that mean for the loads I apply to the system?

[moahmed]

and if you actually understood the practical application of theory you would realize that T/theta = kt = JG/L. You are going down a rabbit hole of non-value added analysis.

you need to stop worrying about semantics and start thinking about how to logically setup an engineering problem. Calculating, measuring, or modeling some kind of a metric is meaningless without some kind of idea of how that result is useful. and once you have that understanding the problem (usually) becomes straight-forward.

Here's a partial list of questions you need to answer for yourself:

Why do I need a calculation of torsional stiffness?

How stiff is stiff enough?

How can I setup an FEA simulation that is both meaningful to real world operating conditions and can be easily verified in the lab?

Is my system linear? and if it is linear what does that mean for the loads I apply to the system?

By torsional stiffness calculation you can determine whether your design will withstand the dynamic loads applied to it or not
The more the torsional stiffness is, the more the efficient chassis you have since experiments have showed that drivers of cars with torsional stiffness below 1600 ft-lbs/deg often complained of flexibility and a lack of suspension control Plus weight savings for the earlier lower stiffness cars compared to recent cars is not as significant as might be imagined

You can setup a meaningful FEA simulation ONLY when you understand what constraints you should place and what forces you should apply ,where you would apply them to get a simulated real case and the most important where did you get these forces from

And about the linearity of your system as you know as the force you apply changes, the torque and the displacement change
But here you should notice that you are dealing with a torque which means the displacement is angular and this can be taken into account when
Determining the meshing element which is a pipeline as in case of ANSYS ADPL.

[Zac C]

You still aren't actually thinking about the problem.

[Z]

You still aren't actually thinking about the problem.
Yes, I think the OP is finding it easier to just cut-and-paste stuff off the web.

Ah, yes..... Learn to "talk-the-talk" well enough, and pretty soon they make you a Design Judge... :)

Z

[moahmed]

You still aren't actually thinking about the problem.

the problem is there is no problem but we are trying to make things look difficult, after considering your chassis as a shaft fixed at one end and applying a couple on suspension points taking into account the weight of driver and engine and then run the simulation ,,whatever magnitude of force you choose the torsional stiffness still the same