Vibration Energy Formula

[sarclee]

Hi, I have two conducted two random vibration testing with the same profile but different duration.

In Random Vibration, since it is linear analysis, no time parameter is needed... I would like to calculate the vibration energy based on duration and Grms.

Is the vibration energy formula (Energy = Grms^2 x time) correct?

 

[GregLocock]

No. Dimensionally incorrect for a start.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[electricpete]

I was thinking the same thing as Greg. Without knowing something about mass or stiffness I don't think any claims could be made about mechanical power or kinetic or potential energy.

The signals terminolgy power spectral density might lead us to believe that if you integrate under the PSD you get some kind of power, but that's not related to the physics term power.

Victor Wowk uses the terminology "vibration energy: here:

https://www.machinedyn.com/docs/articles/Vibration_Energy.pdf

... I haven't studied it closely enough to understand what he's trying to do.

I think I'd start with what it is you're trying to accomplish

 

[GregLocock]

Wow that's a doozy of a paper. Lost me at the bottom of the first page F=ma only applies at zero frequency!




Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[sarclee]

Thank you for your sharing and comments. I would like to extend the discussion by changing the topic of this thread.

Background:
There was a random vibration testing and the DUT was over-tested with two times higher Grms than the test profile. Screws are broken.... There were some static tests conducted before the random vibration.

Some comments that there might be some fatigue to cause the screws break. However, the screws break at the first Random vibration and it happened about 20second. All the previous tests were static test...

By looking at the photos below, would there be any chance of fatigue failure? Or the screw was broken due to high shear force?

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1716027720/tips/A012_-_20240517_120826_dgmwpw.bmp[/url]

 

[desertfox]

Hi Sarcee

The fixing does have a dull and shiny area which would be similar to a fatigue failure but I can’t be 100%.

It might help if we knew what the fixing was apart of and how the comiponent is loaded?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[monkeydog]

There is a lot of reflection from the light to really be able to see the failed surface.