Frequency range for measuring shock load on frame.

[vechman]

I am measuring the peak accelerations on a small tractor frame when running through a bumpy field. Someone has suggested that the frequency range be limited to 50 or 100 hz because the destructive forces are more prevalent in the lower frequencies. When I measure over a wider frequency range (0-1600 hz), the peak acceleration is 200 m/s². When I measure with a frequency range limited to 50 hz the peak acceleration is around 20 m/s². Which frequency range should I use to accurately discribe the load on the frame.

Thanks for your replies.

vechman

 

[IRstuff]

The low frequencies contain a lot of energy, and would be the ones to cause bending, etc. The higher frequencies wiggle loose all the fasteners.

TTFN

FAQ731-376

 

[GregLocock]

Strain causes fatigue, so it is more useful think about displacement than acceleration, but also number of cycles is imprtant so people look at velocity in the frequency domain.

I doubt you'll get much fatigue related to wheel inputs above 100 hz.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Ron]

I would also look at strain. The strains throughout the frequency spectrum contribute to fatigue. Low amplitude/high frequency can be as bad as high amplitude/low frequency.

Have analyzed failures where the low amplitude/high frequency range had more effect on the failure (wind vibration on transmission structure)