Accelerometer for Impact Test

[jrickert]

In the past we have done crush tests with a compression tester. This won't fly any more. Looks like we have to shell out some money for an accelerometer and logger. Does anyone have any recommendations?

[jrickert]

In the past we have done crush tests with a compression tester. This won't fly any more. Looks like we have to shell out some money for an accelerometer and logger. Does anyone have any recommendations?

[Grant Mahler]

My suggestion would be to not use an accelerometer - that would be an expensive way of doing it. There are other, more elegant ways, several of which are on the forum already, and more are possible if you think.

For example, I would borrow someones (parents?) high speed camera and do a destructive test on a prototype. You can get nearly the same information from a camera as you would the accelerometer.

Alternatively, go to your mat sci dept. and use one of their stress/strain machines to get rates, and do some calculations.

[Drew Price]

Stress/Strain machine = compression tester = Universal Testing System, all the same thing, all slow crush methods. These methods will not fly UNLESS you can prove that your construction is essentially strain rate independent, which may be true for some structures, but is not for many, especially metallic ones.

The UTS method is ok for finding the average deceleration, but to find the peak that is required under the new rules you have to either do some sort of instrumented high speed impact (high speed camera like Grant mentioned is my favorite, as he mentioned cheaper prolly if you can find something with sufficiently high frame rate, accelerometers, strain guages etc), or you will have to find some grad students who will share their plastic deformation model fitting to do a finite element simulation, but then you will have to prove the results are reasonable.

One of our ME manufacturing labs is fine tuning some plastic deformation modelling, but still a fair way off, and not good for doing something crushed so completely as our attenuators, but that's your decision. It's mostly for simulating thin sheet metal forming operations.

Remember that insufficient methodology in the report this year is a good way to lose some design.

Lastly, there was a thread on the equipment people use and the range of accelerometers people use if you want to go that route, I think it was in the 'Static Competitions' section.

Best,
Drew

[jrickert]

There really is only 1 solution. And thats crashing things. Its far more fun. I tracked down an accelerometer.

[Nick Renold]

Some useful answers appear here...
B.3.21.1 Impact Attenuator Testing (http://www.formulasae.org/forums/formula/dispatch.cgi/rules/docProfile/100214/d20081029201720/No/B.3.21.1%20IA%20Test%20Method.doc)