Shock test per MIL-STD-810 - equivalent static load for FEA
Shock test per MIL-STD-810 - equivalent static load for FEA
(OP)
Hi all,
An earlier posting in 2007( thread384-192610: Functional shock test per mil-std-810 - equivalent static load )by someone on this very same topic had some good responses out of which I could relate to Spongebob007 's reply the best.
I can extract Natural Frequencies using FEA software. For simple shock tests (such as 40g over 10 ms)could I not make use of this frequency info and come up with an equivalent static G load which could then be applied for a stress analysis ? I understand random vibration is a whole different ball game. I believe there are simple and clever ways of doing just about everything and you just have to keep looking if you don't find them.
Any simple example would be highly appreciated. There was something missing in the earlier Spongebob007's response (don't know how he came up with the 1.667)and I know he is on this planet somewhere but can't locate him though.
thank you,
DonkeyDude
An earlier posting in 2007( thread384-192610: Functional shock test per mil-std-810 - equivalent static load )by someone on this very same topic had some good responses out of which I could relate to Spongebob007 's reply the best.
I can extract Natural Frequencies using FEA software. For simple shock tests (such as 40g over 10 ms)could I not make use of this frequency info and come up with an equivalent static G load which could then be applied for a stress analysis ? I understand random vibration is a whole different ball game. I believe there are simple and clever ways of doing just about everything and you just have to keep looking if you don't find them.
Any simple example would be highly appreciated. There was something missing in the earlier Spongebob007's response (don't know how he came up with the 1.667)and I know he is on this planet somewhere but can't locate him though.
thank you,
DonkeyDude





RE: Shock test per MIL-STD-810 - equivalent static load for FEA
RE: Shock test per MIL-STD-810 - equivalent static load for FEA
As such it is very sensitive to the estimate of the damping, if the frequency content of the shock is close to the resonance, which given the shape of the spectrum of a half sine is likely.
Pretty sure Harris mentions it as well, if you happen to have that handy.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Shock test per MIL-STD-810 - equivalent static load for FEA
Take the ratio of the structure frequency to the pulse frequency. Select the amplification factor from the chart based on damping and multiply that by the peak acceleration of the pulse.
Not sure where 1.667 came from. Probably a typo.
RE: Shock test per MIL-STD-810 - equivalent static load for FEA
Why not? This is done on a transient analysis and you have to create the profile of the signal and apply it to your model.