Impact Attenuator Calculations

[Running Mike]

Somebody asked for a video of Al honeycomb being tested. You can find one in the bottom of this page:

http://www.unicorn.aau.dk/nyheder/2002811

We tested different types and concluded that honeycomb is perfect if you use the right type. The video shows a pre test experiment with Al comb from a wing of a F16 fighter jet.

And yes, the report is a pass or fail thing.

[vane]

Hi, My name is Vanessa. I was wondering how you guys test you impact attenuator and wich method do you use to measure deformation and desaceleration. Thanks for your help

[Luke_Morrow]

Originally posted by vane:
Hi, My name is Vanessa. I was wondering how you guys test you impact attenuator and wich method do you use to measure deformation and desaceleration. Thanks for your help

After testing a number of ways over a few years, we found that dropping a 300kg 44-gallon drum half full of reinforcement and cement from a forklift onto the test piece proved the most effective results. A quick release was used to drop the drum, and a safety rope was used to prevent the drum from falling over. A high speed camera at 1000 fps and rule in the background were used to record data (knowing time and displacement its easy to get initial velocity, then deformation displacement and then average acceleration is easy).

A sheet aluminium fabrication (riveted or welded) absorbed next to no energy, expanded foam absorbed a small amount of energy while it disintegrated like an imploding building without stopping the drum and an aerolam and sheet aluminium alternating stack ~ 200 mm thick stopped the barrel before it hit the ground, absorbing 108 kJ of energy at a constant 16G.

This is also a great opportunity for a risk assessment! Remember, safety first.

[Ricardo Avila Ibarra]

Hi everyone.
I was wondering if any of you knows if we are allowed to present impact attenuator test data from a scale model.

I was actually planing to use only 10 percent of the load determined for the test. Lets say build an impact attenuator scale model 1:10 and drop 30 kilograms instead of 300 kilograms. Obviously using the same drop height.

Thanks in advance

[Luke_Morrow]

Scale testing is easiest when you scale the energy (in your case the mass) and use a cross section of the same scale (1/10th). The IA length needs to be representative. So, yes you can scale the energy, but don't scale the length. This is because your IAD should also validate that the mass comes to rest in less than the IA length.

I am putting together a little document on IAs for FSAE-A and hope to make this available for all teams at the event, to take into consideration next year. Watch this space.

[Tech Guy]

I think the answer is in Question and Answer # 4 of FAQ # 104, which can be found at:
http://www.formulasae.org/forums/formula/dispatch.cgi/r...%20Test%20Method.doc

[mittalrdx]

Hi,
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