Realist waveform to simulate shock

[Tunalover]

Folks-
I'm in the electronics business and have almost entirely used the half-sine pulse, 11ms duration as the waveform for shock simulation on electronic equipment. Does anyone have any historical data to show where this comes from?

Secondly, I have noted that disk drive manufacturers have gravitated to stating the same shaped waveform (half-sine pulse) but with much shorter durations and larger amplitudes. I've seen 2-6ms durations quoted by them but the amplitudes are VERY HIGH (>>100Gs). Is this a gimmick that enables them to exaggerate the amplitudes? It seems to me that the average Joe sees, say, 500Gs advertised and would say "WOW!" but the ENERGY contained in the pulse is not so large because of the very small duration. Is anything less than, say, 10ms, an unreleastically short duration for impact shock in electronic equipment? Just wondering if this is marketing manipulation of technical data!




Tunalover

 

[GregLocock]

Half sine is a good approximation to the impact force seen when dropping a SDOF spring mass system onto a rigid surface.

I agree with your second point, one could apply very high g levels at very high frequencies which would not even be seen by the disk mechanism.

Having said that my gut feel is that 10 ms seems a bit on the low side for an upper limit. As a first instance work it out from pi*(m/k)^0.5 .k for most hard engineering things ranges from 1e6 to 50e6 N/m.

Tom's probably got more to say on this.





Cheers

Greg Locock

 

[franck]

Hi Tunalover,

For your information in the satellite industry, very usually we use a half sine pulse of 500g with a pulse duration of 0.5 ms (yes 0.5 ms!). Really, we want to simulate a shock coming from a pyrotechnic source, which usually exhibits its main excitation in the 2000 Hz region (a 0.5ms pulse duration gives you a peak in the SRS at 1700Hz). Now, you can really question of how a pyrotechnic excitation is similar to a half sine pulse excitation. In theory doing this approach is a non sense but a half sine pulse experiment is way less costy than a pyrotechnic one so we are using 6 dBs margins to convince ourselves that the approach is conservative enough….

Best regards,

Franck