How Do You Calculate Bumper Bending in a Car Crash?

[brokenlickz]

Homework Statement

hi all,

Given:
a car is reversing at 4km/h, weight = 1500kg... n whamps into a lamp post. I'm suppose to calculate the bending of the bumper, which is made of AlZn4,5Mg1 material.

bumper is 900mm long n fix onto the car body
dimension : 80x80mm U profile with a 5mm thickness

Homework Equations

The Attempt at a Solution

i assume that we should use the kinetic energy formula which is

E = 1/2mv2

to get the amount of initial energy.

According to the law of conservation energy.

initial energy = final energy
= deformation energy/potential energy + sound energy(neglegible) + heat (neglegible )

from my what I've considered here, i guess i need a force F in order to calculate the bending distance of the bumper.

but from the formulas i have above, how do i go about getting the force F which works on the bumper?

the area underneath the stress strain diagramme of this material wouldn't help much because i couldn't really calculate (accurately) the area after the elasticity limit right?

 

[Jhero]

it is important to approach problems in a systematic and logical manner. In this case, we are given the initial velocity of the car, its weight, and the material properties of the bumper. Therefore, we can start by using the kinetic energy formula, as you have suggested, to calculate the initial energy of the car.

E = 1/2mv^2

However, we must also take into account the fact that the car is reversing, so the velocity would be negative. This would result in a negative value for the initial energy, which is not physically possible. Therefore, we must also consider the direction of the force and the resulting change in velocity.

Next, we must consider the force acting on the bumper during the collision. This force would be the result of the car's weight and its velocity, and would also depend on the angle of impact and the material properties of the bumper. We can use the formula for momentum to calculate the force:

F = mΔv/Δt

where m is the mass of the car, Δv is the change in velocity, and Δt is the time of impact. This would give us an estimate of the force acting on the bumper.

From there, we can use the material properties of AlZn4,5Mg1 to calculate the stress and strain on the bumper, which would help us determine the amount of deformation. The stress-strain diagram would give us an idea of the material's behavior under different forces and how much it can withstand before reaching its elastic limit.

In summary, it is important to consider all the relevant factors and use appropriate formulas and equations to approach this problem. It may also be helpful to consult with engineers or other experts in material science to get a more accurate estimation of the force and deformation.