our 4 poster rig can reproduce a limited bandwidth. Could it be fine anyway for me?
our 4 poster rig can reproduce a limited bandwidth. Could it be fine anyway for me?
(OP)
Hi all,
I have installed strain-gauges on the axle of a commercial vehicle to measure the vertical and the horizontal loading. I placed them in order to reduce the cross-sensitivity at lowest as possible. I need to reproduce the measured loads with a 4-poster rig. Unfortunately the maximum reproducible frequency by our rig is 20 Hz. I need to know if our rig can reproduce the loading history correctly, therefore I have in mind to compare the pseudo-damage of the loading history with the one of the filtered loading history with a low pass filter with a cut-off frequency of 20Hz. it is the right way to proceed, isn't? Otherwise may you provide me a better one?
Thanks
Cheers
Pietro
I have installed strain-gauges on the axle of a commercial vehicle to measure the vertical and the horizontal loading. I placed them in order to reduce the cross-sensitivity at lowest as possible. I need to reproduce the measured loads with a 4-poster rig. Unfortunately the maximum reproducible frequency by our rig is 20 Hz. I need to know if our rig can reproduce the loading history correctly, therefore I have in mind to compare the pseudo-damage of the loading history with the one of the filtered loading history with a low pass filter with a cut-off frequency of 20Hz. it is the right way to proceed, isn't? Otherwise may you provide me a better one?
Thanks
Cheers
Pietro





RE: our 4 poster rig can reproduce a limited bandwidth. Could it be fine anyway for me?
However within those limitations yes your approach makes sense. Are you driving the hubs directly or do you have the vehicle sat on tires (in which case the 20 hz won't matter much as you are isolated by wheelhop)
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: our 4 poster rig can reproduce a limited bandwidth. Could it be fine anyway for me?
Thanks for your reply. Our 4 poster rig drives the hubs directly. What is the best approach? I filtered few signals with low pass filters with different cut-off frequency and then I calculted the damage with Miner law: I expected that higher was the cut-off frequerncy and higher was the damage, but it wasn't always true. I read on this paper: Fatigue Life Modelling and Accelerated Tests for Components under Variable Amplitude Loads (you can download it here, that spectral filtering can lead erronuos fatigue life results due to filter roll-off and phase shift. So what is the best approach?
thanks
Cheers
Pietro
RE: our 4 poster rig can reproduce a limited bandwidth. Could it be fine anyway for me?
Driving the hubs directly gets rid of the wheelhop problem, but to get realistic fatigue lives we use multi dof excitation of each hub, at least 3 and maybe 5.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: our 4 poster rig can reproduce a limited bandwidth. Could it be fine anyway for me?
The vehicle I have to test doesn't have any suspension system, just a pivoting front axle and a rigid rear axle. Yes the fatigue damage is better represented by a rainflow analysis, but I can't assess if I can get rid the frequency higher than 20Hz with this method.
I will excite each hub with a vertical excitation. In the paper before-mentioned it is stated:
"Successful fatigue editing is also possible by combination methods. As an example, frequency correlated damage based filtering can remove cycles whose frequency cannot be achieved and the resulting filtered multi-channel time series set can be further processed in time correlated damage editing to produce reduced time series as the first set of targets for iterative transfer feedback control."
Do you know any reference material of the "frequency correlated damage filtering"?
Thanks
Cheers
Pietro
RE: our 4 poster rig can reproduce a limited bandwidth. Could it be fine anyway for me?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: our 4 poster rig can reproduce a limited bandwidth. Could it be fine anyway for me?
thanks for your reply. Hopefully someone could give me a tip.
Cheers
Pietro
RE: our 4 poster rig can reproduce a limited bandwidth. Could it be fine anyway for me?