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Home > Forums > Mechanical Engineers > Activities > Mechanical Acoustics/Vibration engineering Forum

Explanation for change in magnitude after random vib test

Read More Threads Like This One

Astorite (Mechanical)

31 May 12 17:34

Hi,

As a small company and being new to vibration testing, we are having difficulty in explaining to our customer the reason for a change in magnitude on a post random low level Sine test. The background is that we complete a functional test on the equipment, Pre LLS test (0.5g @ 20-2kHz), Random vib, post LLS test and then a post functional test. Both X & Y axes were fine with correlation on the pre/post vib plots and the post functional test was fine for all 3 axes. However, in the Z axis, the magnitude at resonance reduced by approx 50%. There was a minimal change (~2%) in resonance for the pre and post plots. The unit wasn't altered nor moved during the z axis testing.

The customer specification allows a deviation of 10% on frequency and 40% on magnitude. As we are outside this, it's a test failure.

As far as an explanation, the reduction in magnitude suggests some settling of the unit in this axis provided additional damping.

Any other thoughts /experiences?

GregLocock (Automotive)

31 May 12 17:55

I suggest you post the plots for all 3 axes pre and post test

Cheers

Greg Locock

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Astorite (Mechanical)

1 Jun 12 4:47

As requested, I've attached the plots for the Z axis LLSS (as I have these to hand). I've also attached a summary table for the pre/post results in the other axes.