Effect of selfweight in strain gauge measurements

[suviuuno]

Consider boom with stain gauges glued at the support of the boom.You know the weight of the boom and all the accessories. Let's say you do zero balance when boom is horizontal pointing straight ahead. Now you move the boom into known positions and as a result you get known strains. I feel it should be possible to figure out the effect of selfweight by this method. Does anybody have experience in these type of issues?

Sure, I could use FEA to figure out the effect of selfweight. Instead, I will to use FEA to check the validity of my measurements.

suviuuno

 

[BobM3]

It's just doing the FBD to get the loads and moments at the strain gage location.

 

[suviuuno]

BobM3,

I partly disagree with you. Your method will work if strain gages are way off from stress concentrations when measuring nominal loads.
If we are after hot-spot stresses, gauges are located close to weld toes as in most cases in our industry. It would be impractical to build FBD due to different stress gradients.

I am fairly confident that one could build a system of equations to figure out the unknown, selfweight. This could be accomplished by moving boom/structure into different positions and recording strains. I do not have solution yet.

Thanks.

 

[itsmoked]

Seems to me that it would be better to weigh a known load in those different positions and then weigh a second load and extrapolate from those. Like horizontal 100kilos then 200 kilos. But not with just the original boom.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com