Assignment 1 In all but a very few vehicles today crush or crumple zones are employed as a method to reduce energy transfer to the occupants in a crash. For the most part crumple zones form a...

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Assignment 1
In all but a very few vehicles today crush or crumple zones are employed as a method to reduce energy transfer to the occupants in a crash. For the most part crumple zones form a structural part of the car such as frontal rail or rear bumper beams. In the early stages of development these crumple zones can be designed via a series of equations that take into account materials properties and geometrical features.
This assignment consists of the following three sections:
1- Using an envelope of 500 mm design a crumple zone that is capable of absorbing ~7,500 Joules of energy at 40 km/h. You can choose any geometrical shape and material to achieve this, but all choices have to be backed up by analytical equations. Use a crush distance of 75% of the original tube length (ie. 375 mm). Make sure if you use a strain-rate sensitive material you include this into your calculations.
2- Depending on your material choice do the following:
a. If you choose a metallic material for a single lobe of deformation show how stress and strain profiles and ultimately fracture (if occurs) progress through the deformation, show this via explanations, calculations and images
b. If you choose a composite material show how the fracture mechanisms/stress/strain work through lobe or ribbon formation; again show this via explanations, calculations and images


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Assignment 1 In all but a very few vehicles today crush or crumple zones are employed as a method to reduce energy transfer to the occupants in a crash. For the most part crumple zones form a structural part of the car such as frontal rail or rear bumper beams. In the early stages of development these crumple zones can be designed via a series of equations that take into account materials properties and geometrical features. This assignment consists of the following three sections: 1- Using an envelope of 500 mm design a crumple zone that is capable of absorbing ~7,500 Joules of energy at 40 km/h. You can choose any geometrical shape and material to achieve this, but all choices have to be backed up by analytical equations. Use a crush distance of 75% of the original tube length (ie. 375 mm). Make sure if you use a strain-rate sensitive material you include this into your calculations. 2- Depending on your material choice do the following: a. If you choose a metallic material for a single lobe of deformation show how stress and strain profiles and ultimately fracture (if occurs) progress through the deformation, show this via explanations, calculations and images b. If you choose a composite material show how the fracture mechanisms/stress/strain work through lobe or ribbon formation; again show this via explanations, calculations and images



Answered Same DayDec 20, 2021

Answer To: Assignment 1 In all but a very few vehicles today crush or crumple zones are employed as a method to...

Robert answered on Dec 20 2021
98 Votes
Part-1
We have speed v = 40 km/hr = (100/9) m/s.
Energy to be absorbed by impact is ~7500 J.
Now, kinetic en
ergy before the impact is = 0.5 * mass * speed2.
Equating the above two gives that the mass of the colliding object is about 121.5 kg.
Now, the vehicle stops by 375 mm. Hence the stopping distance is 0.375 m. Now,
the speed is v which is reduced to 0 in time t.
Thus, the deceleration is (speed-0)/time t.
If the deceleration is called a, and the stopping distance is d then as per the equation
of dynamics, we know that d = v*t – 0.5*a*t2.
Putting a = v/t gives that d = vt – 0.5*v*t = 0.5 * v * t.
Thus, t = 2*d/v = 2 * 0.375 / (100/9) = 0.0675 second.
Putting this value in the equation of a gives, a = v/t = (100/9)/0.0675 = 164.61 m/s2.
This gives the force equal to mass*deceleration = 20000 N = 20 kN.
Thus, the crumple zone has to compress by 0.375 m in 0.0675 seconds under the
action of 20kN dynamic force.
Now. The strain rate the material has to undergo is = strain/time = 0.75 /0.0675 =
11.11 s-1.
Let’s by guess choose aluminium as the material for our crumple zone. From the
available...
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