Calculate Crumple Zone Rigidty?

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SUMMARY

The discussion focuses on calculating crumple zone rigidity using the equation FcosxΔd = ΔEk. The user calculates the kinetic energy of a vehicle weighing 2000 kg traveling at 22 m/s, resulting in -484,000 J of energy. By substituting the crumple zone length of 0.70 m into the equation, they derive a constant force of 691 kN, which they propose represents the crumple zone rigidity. The user questions the accuracy of their approach and considers practical measurement methods, such as using a hydraulic ram.

PREREQUISITES
  • Understanding of kinetic energy calculations
  • Familiarity with the work-energy principle
  • Knowledge of basic physics concepts, including force and angle
  • Experience with practical measurement techniques in automotive engineering
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  • Research the principles of crumple zone design in automotive safety
  • Learn about the use of hydraulic rams for measuring material rigidity
  • Explore advanced calculations for energy absorption in collisions
  • Investigate the role of angle in force calculations during impacts
USEFUL FOR

Automotive engineers, safety analysts, physics students, and anyone involved in vehicle design and crash safety testing will benefit from this discussion.

AJ22
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Homework Statement
Given the change in kinetic energy and distance, find the constant force needed in the crumple zone to stop the vehicle.
Relevant Equations
Work Energy Theorem: W = ΔEk
W = FcosxΔd
The vehicle comes to a stop after the collision so my kinetic energy is equal to (2000kg)(22m/s)2 / 2.
(Ekfinal -Ekinital)
I used the equation FcosxΔd = ΔEk. Knowing that the kinetic energy is -484000J and the length of the crumple zone is 0.70m, I can substitute those values into the equation.
Fcosx(0.70) = -484000.
My question is what would be the angle in the equation of W = FcosxΔd. During a collision the force from a wall acts in the opposite direction from the force of the crumple zone? So the angle is cos180 degrees = -1. Is this right?
So the constant force would then be F = -484000/-0.70 = 691Kn?
That means this number is also the crumple zone rigidity.
 
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All looks good.
 
Is that how crumple zone rigidity is calculated??
 
AJ22 said:
Is that how crumple zone rigidity is calculated??
In practice? I don’t know. It might be measured simply by squeezing it with a hydraulic ram.
 

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