Data acquisition for calculating fatigue life

[davidmandis]

Hi,
I need to carry out a fatigue life analysis on an automobile seat and would like to know how I can measure the stress amplitudes it is subjected to. I guess an accelerometer would need to be used but am not sure which would be the cheapest way to record the data. Can anyone give share their experiences with data recording for the calculation of fatigue life or suggest a suitable technique to do so.

Thanks,
David

 

[GregLocock]

Deriving anything useful from acceleration data for strain data is very hard.

Can you not justify maesuring strains, or forces, directly?

Cheers

Greg Locock

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

 

[rb1957]

there are many systems out there for collecting loasd data ... SoMat is one (i'm not associated, just used them in the past), they are quite cheap, and easy to use. google "fatigue loads data collection", then come back here to see if people can recommend one of your options.

i presume that you want to measure the applied load so you can investigate your whole seat ... if you have a key details that you're interested in, strain guages would collect the targeted information (in my business we'll often collect both applied load and local stresses, usually this only leads to endless argruments over why the model doesn't match reality !)

 

[CoryPad]

This company's products are very common in the automobile industry:

http://iotech.com/

I agree with Greg that an accelerometer is not best suited to this purpose. Strain gauges can be relatively inexpensive. Vishay is the leader in this area:

http://www.vishay.com/strain-gages/

Vishay also make data acq systems that compete with IOtech.

Regards,

Cory

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

 

[reidh]

We have used both IOTech (which is now part of the NI family) and SOMAT in the past. IOTech is a bit simpler to set up in my opinion, but the SOMAT supplied software seems to have more capability.

-Reidh

 

[davidmandis]

Thanks everyone for the help! I would need a force-time history for the fatigue analysis in ANSYS Workbench and a displacement-time history for tuning the spring and damper stiffness of a truck seat suspension system. We will be mounting the kit on the seat to get the readings, so I don't think a strain gauge will be useful. Do any of you know approximately how much the whole kit would cost for the IOTech and SOMAT(nCode)? Also is it possible to use IOTech or SOMAT to control the damper stiffness in real time using a closed loop feedback system?

Thanks,
David

 

[rb1957]

humm, you're looking to tune the spring and damper based on the input from on top of the seat ... i appreciate you're looking at ride comfort, but won't the seat play a significant role ? if you don't de-couple the two flexibilities (the seat and the suspension), i think you'll be missing a big part of the problem (and its solution) ... and these systems are pretty cheap ($10k, maybe $20k) adding another acc. channel doesn't affect the price much (not much more than another sensor).

i don't think these systems provide the active control you're looking for ... that would be a separate controller.