Symmetry of pk-pk mV strain gauge time history?

[ezikial519]

Does anyone have experience of the symmetry (or lack thereoff) for time history plots of the pk-pk total mV from a strain gauges?

Does a non symrmetrical, e.g strong positive bias in the total mV pk-pk time history plot, indicate a possible poor gauge reading? I do not mean a dc offset where the time history plot still looks symmetrical but is no longer centred on 0mV.

The response is not from a single mode but a number of modes.
Any Ideas?

 

[objengrs]

Yes, I've seen strain readings that are asymetric. Usually they have indicated that the loading pattern is also not zero centered. An extreme example would be the forks on a lift truck in bending (ie. the environment is heavily biased toward downward loading, with typically very little upward). You can also get similar results on certain vehicle components that see many g's upward accel. when going over a bump in the road, but don't rebound with similar levels because they only accel. downward due to 1 g gravity.

What's the application?

 

[GregLocock]

Another example would be a strain gauge in the vicinity of the jounce bumpers on a car. The upward stresses will be a lot higher than the downward ones, as the jounce bumper only operates in one direction. Cheers

Greg Locock

 

[ezikial519]

Thanks guys its been useful. The application was a high pressure turbine disc. I wasnt expecting a significant load bias but its something to think about.

I havent been able to isolate a mode and a high component of direct forceing due to gas loads might possibly explain the load bias.

TTFN