Torsional Frame Stiffness Calculation

[Brock Wilt]

Hello All,

I am writing from the University of Cincinnati in regards to the torsional stiffness of the frame. I read a paper from Cornell called "Design, Analysis and Testing of a Formula SAE Car Chassis." In the report, torsional stiffness is calculated as F*L/rotation in degrees where F is the force applied to one side of the frame front suspension point and L is the distance from this point to the center of the frame. Typically a force couple converts into a torque as F*L where L is the length between the 2 forces. Is there anyone from Cornell that could comment on this equation and why it is as such? If not, are there other frame guys on this list? If so, how are you calculating the torsional stiffness of your frame? Thanks.

[Brock Wilt]

Hello All,

I am writing from the University of Cincinnati in regards to the torsional stiffness of the frame. I read a paper from Cornell called "Design, Analysis and Testing of a Formula SAE Car Chassis." In the report, torsional stiffness is calculated as F*L/rotation in degrees where F is the force applied to one side of the frame front suspension point and L is the distance from this point to the center of the frame. Typically a force couple converts into a torque as F*L where L is the length between the 2 forces. Is there anyone from Cornell that could comment on this equation and why it is as such? If not, are there other frame guys on this list? If so, how are you calculating the torsional stiffness of your frame? Thanks.

[Erik Whoa]

That is how we our doing it. I don't think I understand your question.

[Jersey Tom]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">In the report, torsional stiffness is calculated as F*L/rotation in degrees where F is the force applied to one side of the frame front suspension point and L is the distance from this point to the center of the frame. Typically a force couple converts into a torque as F*L where L is the length between the 2 forces. </div></BLOCKQUOTE>

One side only.. thus no couple. If you were to apply a couple using the same magnitude force on the other side of the chassis, for small strain you'd probably see twice the displacement and it would work out to the same number either way.