Monthly Archives: June 2012

Loadcell adapter plates and the challenges of load constraints

Richard Nakka asked that I run FEA on some plates he’d designed to convert a button-type loadcell into something that could be used for 5000lbf tension testing. It consisted of three 0.375 aluminum plates. Two identical ones on the outside that I named “bread”, and one larger one on the inside that I named “meat”.

I wanted to show the difference in FEA between loading the easy way, into faces of the single part, vs. a more accurate way, into a simulated bolt and loadcell button.

First, here is the meat plate loaded with 5000lb stretching it, with the entire inner surface of the drilled hole applying 5000lb to the right and the rectangular surface of the rounded square hole fixed:

Factor of safety:

Tensile stress:

The plots show that the factor of safety is generally greater than 1, so it won’t deform the part. But while this is a very easy simulation to set up, such that you can do it in the Solidworks “SimulationXpress”, it isn’t a realistic simulation. Essentially, what you’re saying here is that when you put a bolt through the hole it will not only push on one side of the hole, but also be bonded to and pull on the other side of the hole. Bolts don’t do that.

To set up a more realistic simulation, I created parts to mock up a loadcell button and a bolt through the aforementioned hole. Here are the same plots, but instead with the force applied to the back of the button and the bolt fixed on either end:

Factor of safety:

Tensile stress:

The scales are the same in both sets of images. The latter set shows that applying the force through a button and 0.24″ rod significantly changes the stresses in the part. The aluminum plate will definitely yield behind the bolt, though it probably won’t fail. This is a result you can only really find with the extended Solidworks Simulation, as Simulation Xpress doesn’t allow multi-part assemblies.

Finally, and less interesting, here are the same plots for the ‘bread’ plates:

Factor of safety:

Stress:

And finally a view of how the part will stretch as a spring, with the colors representing how far the various areas of the part will move from their original location:

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