impact attenuator testing

[89er]

I am part of design team for the FSAE team and our team is heading for the FSAE-A competition in decemeber this year. We are facing some problem with the testing of impact attenuator and hence have a few queries
1. Is FEA sufficient for impact attenuator?
2. Is physical testing of the IA compulsory?

Thank you

Vineet Kumar
Design Validator
PEC FSAE Team 2009-10
Chandigarh
India

[89er]

I am part of design team for the FSAE team and our team is heading for the FSAE-A competition in decemeber this year. We are facing some problem with the testing of impact attenuator and hence have a few queries
1. Is FEA sufficient for impact attenuator?
2. Is physical testing of the IA compulsory?

Thank you

Vineet Kumar
Design Validator
PEC FSAE Team 2009-10
Chandigarh
India

[Shashi]

I am not the attenuator guy, but I think a physical validation is necessary. We had ours done in ARAI, Pune and from the feedback the team that came back from the competition, the judges were pretty impressed by the physical test specimen.

[exFSAE]

I would not use unvalidated FEA in a very dynamic, high-strain, plastic deformation event.. particularly if you're using any composites or weldments.

In other words.. just build it and drop test it with some appropriate mass.

[Shashi]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> I would not use unvalidated FEA in a very dynamic, high-strain, plastic deformation event.. </div></BLOCKQUOTE>

I am not sure how significant the attenuator is during the competition, with safety being the primary intention.

The last years team spent a hefty sum on getting the attenuator tested that cost us more than the tire data. At the test facility, they'd used a high speed camera to detect the deceleration, force and other parameters. Maybe accelerometers would've been a financially better solution.

[Shashi]

The above is in no way to undermine the significance of physical validation of computer aided testing. It was just to vent out that there are cheaper solutions out there!

exFSAE - Would like to hear from you, how you guys test your attenuators?!

[exFSAE]

We spent $0 to get our attenuator tested.

Pretty simple. We walked down to the Civil Engineering wing. Told em what we wanted to do. We put our crush zone down on some re-enforced concrete. We put together some large steel weights into a big "slug" that weighed the required 600 or however many pounds. Hauled it up 8' or however much in the air, and dropped it.

At the time (2006, 2007) the only requirement was that the average deceleration be less than some amount (20G I think). We measured the initial and crushed size of the thing, and knowing the initial impact velocity.. we came up with a figure for average deceleration.

If there's a peak decel requirement now, then yes, having a high range accelerometer would be the way to go. I believe some were even available in our MechEng department.. use would have been free of charge.

Bottom line, if you know where to look and who to talk to, it shouldn't cost anything to test the things. I think we even scrounged up enough scrap and remnant material from around the MechEng, Civil, and Aero shops to build our test pieces for basically nothing.

[Shashi]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">We spent $0 to get our attenuator tested </div></BLOCKQUOTE>

Sweetest thing I've read in quite some time. So what material did you use for the attenuator?

We had used an FRP shell with a conical polypropylene core. The shell was a cubic shaped structure housing the hollow, tapered, cylindrical polypropylene core.

[fixitmattman]

Physical test data is the most convincing way to go about it. Given the possible variation of an FEA model to the physical object I can't see the judges going for it. While you don't have to do a drop test, physical testing is strongly implied in the language of the rules.

For what it's worth it's not too much work to get some scaffold for a weekend, build a tower, and drop some weight. Accelerometers and the other equipment for the data acquisition should be on hand at the university or easily borrowed within depeartments.

[exFSAE]

I believe one of the designs that worked the best included..

<UL TYPE=SQUARE><LI>Some welded 1/2" 4130 tube contraption, with a backing plate.
<LI>A variety of empty green bean cans
<LI>Expanding foam
<LI>Chicken wire
<LI>Maybe some angle iron?[/list]

Another one that worked was a couple layers of CRFP thrown together in a "nose cone" shape, filled with more expanding foam.

I believe we went with the latter for weight..

[Grant Mahler]

Nevermind.

[Hector]

Our civil department has this big pendulum - think of it as a battering ram suspended by wires. You mount your specimen to a beam, and the pendulum swings downwards, connecting with the specimen at the bottom of the arc, when the pendulum is traveling horizontally.

A couple guys on our team had some cool DAQ boards that they got from a mechanics of materials lab; they hooked up a few accelerometers and measured decel. Didn't cost us anything except time (the civil department hadn't actually set up the pendulum yet, we set it up in return for using it first.)

[89er]

Thank you for your inputs- Shashi, exFSAE. Will be done with the physical testing today.

Vineet Kumar
Design Validator
PEC FSAE Team 2009-10