Impact Attenuator

[Metzker1988]

Hello,
I hope you guys can help me? I tested my Impact Attenuator at the Federal Highway Research Institute in Germany. I got a graph Acceleration [g] vs. Time [ms]. Is it possible to calculate from this data a force-displacement curve?

[Dash]

I'm assuming probably not due to the material yielding/failing being highly non-linear. I know you could put it back to force vs. time knowing the mass of the sled used. If you have an after test deflection, you could maybe see about trying to backtrack and fit a curve to the data. But that would suck ( and not be very correct ).

[RobbyObby]

Dash is right, you could manually back track each data point and figure out force if you know the mass of the sled. Also, in order to make a graph, you have to start with a data set, so if they didn't give you the data, I'd see if they can get that to you. Since they're a reputable institute I imagine it won't be hard for them to get that to you. It's much easier to analyze a data set than it is to analyze a graph.

[Z]

Originally posted by Metzker1988:
...
I got a graph Acceleration [g] vs. Time [ms]. Is it possible to calculate from this data a force-displacement curve?
Dash "... probably not ..."

RobbyObby "Dash is right..."

You guys have got to be kidding! This is high school stuff!!!

Geez!!!!!... http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif
~~~o0o~~~

Metzker,

What is Newton's 2nd?

What is the relationship between acceleration, velocity, distance, and time?

Are you sure you want to do engineering???

Z

[Buckingham]

Homer: See Marge, I told you they could deep fry my shirt.
Marge: I didn't say they couldn't, I said you shouldn't!

Z is correct, pretty basic math. However, it would be extremely poor methodology, and no reputable test lab would ever advise to use an impact accelerometer to accurately represent displacement. Noise and uncertainty will propagate very quickly when you double integrate the acceleration data.

[Tim.Wright]

If you had velocity and time it would be better but you can still use acceleration if you make some corrections to the signal.

If you know the original length of the impact attenuator and the final crushed length you can find the deformation distance. Then you can apply a correction to the accelerometer reading until the double integration = the deformation distance.

In any case, if you dont know the mass of the sled you're stuffed.

Tim

[Dharma]

I think that the best thing to do is starting from the force-dispacement graph, and then, knowing the mass, establish the decelerations.

[mittalrdx]

Hi,
Can u guys help me out too?
I just wanted to know that for the destructive testing of the impact attenuator can we give more than 7350J of energy and have some bounce back i.e.(give approx 9000J of energy and have a bounce back energy of 1600J) and still say that the impact attenuator absorbs 7340J of energy thus it works fine?


cheers
shivam

[Canuck Racing]

Mittalrdx,

It's a sign of a poor and dangerous design but it does meet the rules. And as you don't have to show any data post crash (I could be wrong there but don't have time to check the rules...) there is no way for anybody to catch it as an unsafe design in tech.

Time for an ethics decision...

[mittalrdx]

Canuck Racing

Canuck Racing
thanks.