Notching during Sine Testing 1

[sirbrandon]

This may be a basic question, but I have been struggling with it the past few weeks. I am working on a spacecraft project (and I am new to this industry), and there are some concerns that when the spacecraft is subjected to the sine sweep qualification testing, some of the fragile equipment may not survive the test. Therefore, given the input sine sweep profile that is the test requirement, how do you go about notching the levels down to something "less damaging" and yet meeting the test objective i.e. to qualify the equipment to launch loads. I have been reading about force-limited testing, but I think this method is more suitable for random vibration testing. I have seen some materials pertaining to sine sweep testing, but there's little information on how to derive the notch profile. Any pointers would be deeply appreciated. Thank you.

 

[IRstuff]

?? IF you are doing the sine sweep per spec, you CANNOT notch the test conditions. The fact that your hardware is too fragile says that you must redesign it, or cushion it with isolators, etc.

TTFN
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[sirbrandon]

From what I understand, notching is frequently done to prevent overtesting to the equipment, due to the mismatch in the impedance between the shock table and the device under test. The objective is to ensure that the device is tested to to the "appropriate" qualification levels. I'm having problem figuring out what is the "appropriate" level to test the device... ensuring the device is flight-worthy but not overtesting it.

 

[IRstuff]

Whatever launch platform your payload is designed for, there are specifications from the platform provider that tell you what the launch environment is. There should no notching required of the tester, since it's under direct, closed-loop, control. If notching is required, go to another testing facility. Likewise, if your tester cannot guarantee its input programming go to someone else; unless a major error occurs, there should be no "overtesting" of your hardware, unless it's under-designed.

TTFN
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[IRstuff]

For sine dwell, the typical process is to run it at a substantially reduced amplitude first, to make sure the hardware isn't incorrectly designed, and then slowly increase the amplitude to the full specification.

TTFN
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