Using shaker table to verify dynamic frequency based strain

[CaptainCrunch]

I purchased an IOTech strain book with the intent of measuring strain of components on a shaker table (3300 lbf single axis TIRA )and on lawn and garden applications during normal usage. This would be used to verify that the shaker was replicating the strain levels seen in the field. Once the strain levels on the shaker are verified to the field the next step is compare strain levels to FEA results.

I currently use ABAQUS mode based solution which gives stress as a function of frequency. I want to compare FEA to test values of frequency based strain. When I take time-based test strain measurements and pass them through a FFT I am getting suspiciously low frequency based test strain values. So I need a way to verify the frequency based strain results I am getting.


To verify this I was planning on putting a gage bar on the shaker table with an accelerometer on the end of the gage bar. The accelerometer would give the displacement at any given frequency. Knowing the displacement the bending stress could be calculated through closed form solutions.
Then I a have a theoretical frequency based solution which can be compared to the value the strain data ac is giving me.

Has anybody came across this before? Does anybody see any issues with this? Feedback would eb appreciated.

TIA,

George Vandyke
Product Engineer
Briggs & Stratton

 

[CESSNA1]

CaptainCrunch: What frequencies are you using to drive the shaker, what is the profile? What are your results? What frequencies do you experct to see?

 

[CaptainCrunch]

Tha shaker will be driven with a low amplitude sign sweep. Say 5 -400 Hz at 0.1 g, sweep rate of 0.2 Hz / sec. I will be looking at all frequencies in this range (resonant and non-resonant). At each of these frequencies the displacement will be given by the accelerometer and be used to calculate the stress through a closed form solution.

 

[CESSNA1]

CAPTAIN CRUNCH: I suggest that you use a low level random profile. I would also suggest several accelerometers on the piece so you can see the response of the different locations. If you shaker feedback accelerometer is on the shaker head you may want to compare its output to the output of the accelerometers on the piece. Sometimes you are better off mounting the feedback accelerometer on the piece rather than the shaker head.

I am curiois is this an entire engine or jsut a part of it? I am assuming there is a attaching fixture between the piece and the shaker table.

Regards
Dave