MIL-S-901 Shock testing

[izax1]

Does anyone have practical experience in tests acc to MIL-S-901D? (Barge test) I just wonder whart is the practical way of measuring the G levels? Will the instrumentation, cabling, recorder etc. fly all over the place? I know you can experience extreme G-levels.

Thanks for any input.

 

[IRstuff]

Never got that far, but the barge never capsizes, so things won't fall out. It should be possible to isolate the instrumentation, since the levels are not that outrageous. E.W. Clements was very prolific, and the following is probably his best known piece:

Shipboard Shock and Navy Devices for its Simulation

DTIC has other stuff from him as well as other shock-related documents.

TTFN
faq731-376

 

[izax1]

No, I was not concerned about things falling out, but rather the practical issue of securing the instrumentation. And I have watched some of the test videos on YouTube. Looks like a really beat up.
Yes, I have been through Clements. Gives some very good insights to the levels and dynamics. But we may now be at the threshold of doing such a test. And this is probably beyond any shock levels we have been "used to". And the difference between theory and practise.......

But thanks for the input.

 

[IRstuff]

I think that securing the instrumentation is mostly about wrapping it with gobs of bubble wrap or something similar. The two Mars Rovers landed on Mars with what is essentially a giant bubble.

If the g-levels inside the insulation go down far enough, you wouldn't need to do anything inside the boxes. Otherwise, you might need to put some sort of foam insulation on the inside of the boxes. You'd also probably need to get solid state drives, of course.

You can probably test your instrumentation ahead of time, by whacking it with a hammer test; you can tune the fixturing to get the comparable levels of shock as the barge.

TTFN
faq731-376

 

[izax1]

Thank you for advice. Yes, doing hammer testing ahead of time is a good idea.

 

[Twoballcane]

I’ve never been to a barge test, but I’ve know folks who witness and instrumented the UUT on the barges. Their rule of thumb is you can never have enough transducers. The transducers are not the only things you have to worry about, you also have to worry how the cables are laid out and some where along the line you have to add an amplifier, because over hundreds of feet, your signal will degrade. You also have to figure out what the upper and lower limit should be for your transducers and signal analyzer triger. You can run the risk of either clipping (your upper limit is to low) or the signal is in the noise (lower limit was set to high). Also, depending on how many degrees of freedom you can experience some insane shock amplifications.

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”

 

[spongebob007]

Never really had to deal with it. For all of the Medium Weight and barge testing we have ever done all we do is specify how many accelermoeters we want and where to put them. The folks at the test lab do the rest.

Do accelerometers fall off? Yes, if you use those little accelerometers that you glue on they will sometimes fall off during a shock blow if you have very high G levels. The accelerometers that you mount on a stud are much more robust, but they are bigger and require you drill and tap holes into your UUT.

For more detailed information you can always call one of the test labs.

 

[spongebob007]

The labs also do all the data processing for us and write us a lab report that we submit to our customer. Sometimes we request raw data for further analysis. I like to get data in UERD format but EXCEL will do. The labs typically have some sort of Labview VI that converts the raw data to a text file or a .urd file.