Impact Attentuator Testing

[JD232]

Hello everyone....

We are competing in FSAE for the first time... can anyone tell me how to go about testing the impact attentuator...

I am not sure on how to prove the average deceleration of less than 20g... we were sort of thinking we will throw the impact attentuator from a height with a weight tied around it... I am not sure how to make the calculations...

[JD232]

Hello everyone....

We are competing in FSAE for the first time... can anyone tell me how to go about testing the impact attentuator...

I am not sure on how to prove the average deceleration of less than 20g... we were sort of thinking we will throw the impact attentuator from a height with a weight tied around it... I am not sure how to make the calculations...

[James Morris]

V^2=U^2+2as and a press with a pressure gauge is a good starting point!

[exFSAE]

Go to your Civil engineering lab (or whatever).. some place with large weights, a hard floor, and some height. Drop the 640lb or whatever it is, at the appropriate height to get the target velocity.. on your impact attenuator. Nothin beats dynamic testing.

Either put an accelerometer on the thing, or just measure how much the attenuator has crushed down. Real easy Physics 1 stuff. Know starting velocity, end velocity, distance.. you know accel.

[JD232]

@James, exFSAE

Yes I understand that bit, and I have been considering the idea of putting it on a UTM (Universal Testing Machine) and doing the newtonian physics.... but I have two problems with it

1) Can pressing it down be construed as impact... cuz totally different mechanics follow in case of impact
2) The destruction of the crush zone may not be uniform... that is in the starting it may be high enough to kill my driver.. than attain a low value to give an overall value of less than required...

@exFSAE
The second problem is still present if we throw weight from height... unless we use an accelerometer
Can you elaborate on putting the accelerometer thing... I am not sure what you mean by that...
Instrumentation is not my fave subject

[Davo]

Theoretically you could have a huge piece of long foam sticking out the front of the car and a house brick behind it and the average acceleration would be less than 20g because the impact would take place over the entire deformation of the foam. Thing is you'd fail tech inspection after the scrutineers stopped laughing at you. I remember hearing something about introducing a rule where there would be a peak as well as an average g limit. I never work on the attenuator so I'm not sure.

[Drew Price]

Davo,

You are exactly right, next years rules stipulate (tentatively of course, in the possible rules changes section) that your IA design cannot subject the car to greater than a 20g sustained deceleration, and cannot peak at greater than 40g.

This requirement will probably mean that you will not be able to use only an UTS machine to do the analysis, unless you know something I do not. You will have to model the impact dynamically, or perform some sort of test.

Best,
Drew

[asahu]

hello,
we are a new team
we have got an impact testing facility but the problem is we have got a 120 kg of mass instead of 300kg as specified in the rules.
so by our inference we have decided to conserve 7350 J of energy.
therfore according to our calculation, the speed at which the mass is moving is around 11m/s instead of 7m/s as specified inthe rules.
is it correct.
please help me out in this.

[Michael Palaszynski]

Looking at how the judging went at VIR, physical test data is key, do it.

[vandit]

for first time we did it by scaling down evrything, like taking scale down model of impact attenuator and also scaled down model of weights being dropped from height...but judges in germany objected that you cant do it by scaling method because the 'foam' that we were using has non linear deformation characterstics and hence a scaled down model cannot be safe approximation for full size ....

i feel the method suggested earlier of dropping 640lbs in cibil lab could do the job...

and regarding UTM, i feel it's not the correct way to determine impact load capacity, because UTM's for testing gradual deformation which is NOT the thing impact attenuator is meant for....

another way to try, could be to use Swinging hammer in metrial testing lab, which is used for impact testing(charpy and Izod)....you can try putting your impact attenuator and allowing the heavy swinging hammer to blowit ....do the necessary calcultion for conservation of energy....