vibration testing 1

[FSB1]

What is the criteria to decide if it would be better to test (or not) an structural item for the following tests:
[ol 1]
[li]Sine testing[/li]
[li]Random testing[/li]
[li]Shock testing[/li]
[/ol]

Typically for structures 2. Random is tested

But sometimes people decide that it is safe to not test 1.Sine, and 3.Shock
What is the criteria to decide not to test for 1. and 3. (or even 2.))?

 

[WARose]

What is the product you are testing (and what is the reason it is being tested)? For most "structural" items, any of the 3 will be ok. (With #2 telling you the most due to the response.)

 

[btrueblood]

Your handle suggests you are an aero engineer, concerned with flight structures. Posting here will get you a lot of comments from people who design buildings.

From a fellow (ex-) aero engineer, my $.02 is: sine testing is usually done to confirm/establish resonances for your structure, and confirm modelling/analysis. Random is done for multiple reasons (transportation/handling loads, operating environment loads, seismic loads). Shock is done for multiple reasons also, i.e. drop testing (somebody kicked the crate off the loading dock), blast loading (your device needs to survive a torpedo hit when bolted to the deck of a ship), and other pyrotechnic events (pyro bolts fire to disconnect upper and lower stages of a spacecraft, that shock travels through the structure to your device). Typically sine and shock testing are done for qualification testing, along with a 1.5x PSD random vibration test, and subsequent production units are typically subjected to a 1x PSD random vibration test.

More details in MIL-STD-810.

 

[IRstuff]

Typically, vibration testing is looking for ways that a system might break. Sine/random is often concerned about resonance that might "break" inertial stabilization, or break the mechanical hardware through fatigue. Shock testing is about directly breaking something, like dropping a ceramic plate onto concrete, or an earthquake breaking bits of a building.

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[GregLocock]

For modal analysis I have used all 3.

Swept sine input is good because it has a very high signal to noise ratio, and since it is only at one amplitude it linearises the response (sort of) of non linear structures. Random is more commonly used, it is usually quicker than swept sine. It can also be used for MIMO. Hammer testing needs the least setup time and is good for roving surveys using multiple excitation points. It can produce the best results as there is no coupling of the shaker to the IUT.



Cheers

Greg Locock


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