Racecar Statics and Mechanics of Solids problem

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SUMMARY

The discussion focuses on the design of a pushrod suspension for a small formula car, specifically determining the required tubing diameter to withstand the loads experienced during operation. The car's weight is 700 lbs with a 60-40 front to rear weight distribution, and it undergoes a 2G turn, resulting in a maximum tire force of 525 lbs. The calculations revealed an incorrect cross-sectional area and yield strength for the 5/8 .035 4130 chromoly tubing, with the corrected yield strength being 70,000 PSI, leading to a recalculated stress of approximately 27,000 PSI under maximum load.

PREREQUISITES
  • Understanding of static equilibrium equations (Ʃf(x)=0, Ʃf(y)=0)
  • Knowledge of stress calculations (σ=F/A)
  • Familiarity with materials properties, specifically yield strength of 4130 chromoly
  • Ability to create and interpret free body diagrams
NEXT STEPS
  • Research the properties and applications of 4130 chromoly steel in automotive engineering
  • Learn about advanced methods for calculating stress in tubular structures
  • Explore the design principles of pushrod suspension systems in motorsport
  • Study the effects of weight distribution and cornering forces on vehicle dynamics
USEFUL FOR

Mechanical engineers, automotive designers, and students involved in motorsport engineering who are interested in suspension design and load analysis.

hks118
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Homework Statement


So I am designing the suspension for a small formula car. It's a pushrod suspension much like what is shown below:
[PLAIN]http://f1-dictionary.110mb.com/Images/pullrod_poshrod_push.gif
I am trying to find the required tubing diameter for the loads the car will experience.

Homework Equations


Ʃf(x)=0
Ʃf(y)=0

σ=F/A

The Attempt at a Solution


The free body diagram
ocx0cl.jpg


The car is assumed to weigh 700lbs, have 60-40 front to rear weight distribution and be in a 2G turn, so the maximum force of the tire is 525lb. θ is assued to be 45°

By the method of joints:

At pinned joint A
Ʃf(x)=0=FLCA-cos(θ)Fp
Ʃf(y)=0=Ft-Fpsin(θ)

At pinned joint B
Ʃf(x)=0=-Fs-Fpcos(θ)
Ʃf(y)=0=-FRy-Fpsin(θ)

So Fp=Ft/sin(θ)

And the maximum force in the pushrod is around 743lb. One of the tubing thicknesses under consideration is 5/8 .035 4130 chromoly which has a yield strength of 70PSI.

Cross sectional area is
∏/4(.625in-.59in)=.0275 in2

Calculating the stress at maximum load is calculated at around 27000 PSI :eek:

I know my statics is rusty but this is wayyyyy off. This tubing thickness is within the range of what other people are using, maybe a bit on the small side. Can anyone point out where I may have gone wrong?
 
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The cross sectional area of the tube is incorrect: A = (pi/4)*(do^2 - di^2)
The min. yield strength for this material is 70000 psi (70 ksi), not 70 psi.
 
Thanks! makes much more sense now.
 

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